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Lee, Wai-Tung. "Neutron scalar Aharonov-Bohm effect and spin density waves in chromium /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901258.
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Haskell, Brynmor Dylan Luigi. "Gravitational waves from deformed rotating neutron stars." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438658.
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Tennant, David Alan. "Neutron scattering studies of spin waves and spinons." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259852.
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GILIBERTI, ELIA. "ON NEUTRON STARS'CRUST BREAKING AND GRAVITATIONAL WAVES EMISSION." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/704603.
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Many different astrophysical events related to pulsars are taught to be due to starquakes, that could be caused by various possible loadings acting on the crust. However, at the present time, there is still a lack of theoretical well based modelling for most of these loadings and, therefore, we have only a very rough knowledge of the physics of neutron stars’ crust response. This PhD work wants to be a first development of a quite realistic calculation of the effects of chosen loadings, being that the forces due to uniform rotation, differential rotation or pinning, on the crust of pulsars. A Newtonian model, already used in Geophysics, has been adapted to the very different physical conditions of neutron stars’ physics and used to describe self-gravitating neutron stars, both in the incompressible and compressible scenario, subjected to different kinds of loadings. In particular, the deformations due to uniform rotation, differential rotation and slack pinning are studied. It is found that the response of the star is very sensitive to the adiabatic index value, while it is weakly influenced by the stellar mass. In all the cases, the strain developed between two glitches is found to be insufficient to break the crust, a result that challenges the standard picture of pulsar glitches based on crustquakes. Finally, attention is focused on accreting neutron stars in low-mass X-ray binaries and millisecond pulsars. The scenario is the following: the star spins up due to the accretion of matter thus building up stress; the mass quadrupole moment associated with crustal failures leads to the emission of gravitational waves which, in turn, spins down the star until equilibrium. The equilibrium frequency calculated is found compatible with observations. It is also argued that these gravitational waves could be potentially detected by the LIGO-Virgo interferometers in the near future.
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Bastarrika, Mikel. "Bayesian analysis of burst gravitational waves from galactic neutron stars." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2363/.
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This thesis summarises my work in relation to data analysis for gravitational wave detection. Most of the personal contribution relates to the assessment of the detectability of potential burst-type gravitational wave signals from the galactic population of neutron stars and to the parameter estimation of the models used to represent these signals. A small part of the work, confined to the last chapter, describes the experimental work carried at the beginning of the research period and aimed to measure the shot-noise level of the modulated laser-light in the gravitational wave detectors. Chapter 1 is introductory and presents generic information about gravitational wave radiation, a postulate of the theory of general relativity. The polarisation of the radiation and the approximate values of amplitudes and frequencies of the signals expected from astrophysical events are presented, together with most important gravitational radiation sources for ground-based detectors. Chapter 2 presents the study on the detectability of burst-type gravitational wave signals incoming from neutron stars located in our galaxy. Three differently shaped galactic neutron star populations are introduced and the detectability of ground-based detectors to signals of different polarisation degree coming from these source populations is investigated. Based on the time- and polarisation-averaged antenna pattern and antenna power values, approximated by Monte Carlo methods, detectability is measured in terms of a) the geographical location and orientation of hypothetical detectors, and b) the current detectors, either working individually or as a part of a network. Also, the sidereal times at which each detector is more sensitive to the sources of the neutron star populations defined are inferred. Chapter 3 introduces a mathematical model of the burst-type gravitational wave ringdown signal investigated in this work, which represents a short-lived gravitational polarised radiation generated by an oscillating neutron star: an exponentially damped sinusoid comprised of a sine and a cosine component, of the same frequency but different amplitude, as the two polarisation components of the signal. The model of the signal is given, in the time- and in the frequency-domain. Chapter 4 is devoted to present the Bayesian probability tools necessary to carry out ‘model comparison’ and ‘parameter estimation’ for the detectability study of our particular burst-type signal. Comparison of models allows choosing the one that better represents the data and subsequently focusing on in order to compute the most likely parameter values of that model. Also, in this section, the way in which the detector data can be simulated in the frequency domain, combining the signal and a noise realisation corresponding to the power spectrum of the noise that characterizes the detector, is explained. The likelihood function for a signal corresponding to one oscillation mode and seen by one detector is derived both in the time- and in the frequency-domain. The nested sampling technique is summarised, a useful tool to compute effectively the marginal likelihood of the hypotheses considered. Chapter 5 presents the results of the model selection and the parameter estimation exercise. The expression of the likelihood is generalised so that it can adopt more than one oscillation mode and been seen by various detectors of a network. Depending whether one, f-mode, or two oscillation modes, f and p, are suspect, two different scenarios of various hypotheses are considered. For each hypothesis the minimum strength of the signal to claim detection is studied and a parameter estimation exercise is carried out to characterise the signal and define the location of the source in the sky. Signals of known parameters and differing strengths were injected into the synthetic noise of three advanced detectors comprising a network. The values of the parameters were estimated using Bayesian inference for two different scenarios: when only the f-mode is suspect (scenario 1), or when both f- and p-modes are suspect (scenario 2). Posterior probabilities of the parameters in Scenario 1 are better defined and constrained than those for Scenario 2, due to the added uncertainty of including another oscillation mode. As expected, the uncertainty of the probability distributions of the parameter values decreases and the mode shifts toward the exact injected value as the signal strength increases. For both scenarios the frequency value can be accurately estimated, but not so well the damping time, especially for the p-mode oscillation, which is suspected to have longer time durations than f-modes, typically several seconds. The ability to estimate the polarisation degree of the signal is also quite limited and strong signals are required for the mode of the distribution to approximate the exact value. Similarly, determining the most probable location for the source is possible in both scenarios. The two-fold degeneracy of the sky position and related to the travel time of the signal to the detectors has been broken; relatively strong (high SNR) signals, especially for scenario 2, are needed for the source location to be constrained with accuracy. Chapter 6 presents the experimental work carried out, by which the measuring of the shot-noise level of differently modulated and demodulated laser light was intended. Due to the poor outcome of this experiment and the lack of useful results the emphasis has been placed on a detailed description of the modulation apparatus, opto-electronic set up and the control system put together. Chapter 7 looks to the future and briefly presents how to take this data analysis work forward.
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Vinciguerra, Serena. "Studying neutron-star and black-hole binaries with gravitational-waves." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8159/.
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The revolutionary discoveries of the last few years have opened a new era of astronomy. With the detection of gravitational-waves, we now have the opportunity of investigating new phenomena, such as mergers of black-holes. Furthermore, multi-messenger observations now allow us to combine information from different channels, providing insight into the physics involved. With this rapid evolution and growth of the field, many challenges need to be faced. In this thesis we propose three data analysis strategies to efficiently study the coalescences of compact binaries. First we propose an algorithm to reduce the computational cost of Bayesian inference on gravitational-wave signals. Second we prove that machine-learning signal classification could enhance the significance of gravitational-wave candidates in unmodelled searches for transients. Finally we develop a tool, saprEMo, to predict the number of electromagnetic events, which according to a specific emission model, should be present in a particular survey.
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Santiago, Prieto Ricardo Ignacio. "Transient gravitational waves at r-mode frequencies from neutron stars." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5530/.
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A search for long transient gravitational waves associated with neutron stars is presented. The estimated length of these sources is from hours to weeks. Two types of astrophysical sources are considered: pulsar timing glitches associated with r-modes oscillations in the interior of isolated neutron stars, and Type I X-Ray bursts in neutron stars from binary systems. These signals follow the model of an e-folding sinusoid signal with a duration dependant on dissipation processes in the interior of the neutron stars and the gravitational radiation reaction. Estimations of the timescales of gravitational wave signals emitted by stable stars are presented. From this study, it is concluded that detecting signals from faster spinning neutron stars is more feasible than from slower neutron stars. The study of this type of transient gravitational wave signals is explored for the first time using an adaptation of the F-statistic gravitational wave search method used regularly in continuous gravitational wave searches. This adaptation, proposed by Prix et al, is a search methodology in which the duration of a signal plays a significant role in its detection. This code is part of the LAL/LAL-apps data analysis algorithm libraries of the LIGO and VIRGO scientific collaborations (LVC). The use of this method in the gravitational wave search presented in this thesis was implemented in two different environments: gaussian noise data and data in gravitational wave detector-like noise. For the latter, injections of long transient signals with durations ∼ 10,000 s on the LVC Engineering Run 3 were done. A comparison between the results obtained in these two studies is presented. It shows that, by having a good characterisation of unwanted noise lines, it is possible to distinguish the frequency of the injected signal within a small search band of only a few frequency bins. On the other hand, the recovery of the duration of the signal would require a broad search band over time. This estimation is set to be approximately ±τ, where τ is the damping time of the injected signal, in order to construct a complete τ distribution. For example, for a signal that last ∼ 3.5 days, an total τ interval of ∼ 6.5 − 7 days is required.
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González, Boquera Claudia. "Neutron-rich matter in atomic nuclei and neutron stars." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/668774.
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The proper understanding of the equation of state (EoS) of highly asymmetric nuclear matter is essential when studying systems such as neutron stars (NSs). Using zero-range Skyrme interactions and finite-range interactions such as Gogny forces, momentum-dependent interactions (MDI) and simple effective interactions (SEI), we analyze the properties of the EoS and the influence they may have on the calculations for NSs.
We start by studying the convergence properties of the Taylor series expansion of EoS in powers of the isospin asymmetry. Next, we analyze the accuracy of the results for β-stable nuclear matter, which is found in the interior of NSs, when it is computed using the Taylor expansion of the EoS. The agreement with the results obtained using the full expression of the EoS is better for interactions with small-to-moderate values of the slope of the symmetry energy L.
The mass and radius relation for a NS is obtained by integrating the so-called Tolman-Oppenheimer-Volkoff (TOV) equations, where the input is the EoS of the system. We have studied the mass-radius relation for Skyrme and Gogny interactions, and we see that that very soft forces are not able to give stable solutions of the TOV equations and only the stiff enough parametrizations can provide 2M0 NSs. We also notice that none of the existing parametrizations of the standard Gogny D1 interaction is able to provide a NS inside the observational constraints. Because of that, we propose a new parametrization, which we name D1M∗, that is able to provide NSs of 2M0 while still providing the same good description of finite nuclei as D1M. A parametrization D1M∗∗ is also presented, which is fitted in the same way as D1M∗ and provides NSs up to 1.91M0.
Moreover, we estimate the core-crust transition in NSs by finding where the nuclear matter in the core is unstable against fluctuations of the density. To do that, we employ two methods, the thermodynamical method and the dynamical method. In the case of finite-range interactions, such as the Gogny ones, to use the dynamical method we have had to derive the explicit expression of the energy curvature matrix in momentum space for this type of interactions. We observe a decreasing trend of the transition density with the slope L of the symmetry energy, while the correlation between the transition pressure and L is much lower.
Finally different NS properties are studied. The crustal properties, such as the crustal mass, crustal thickness and crustal fraction of the moment of inertial have lower values if one computes them using the core-crust transition density obtained with the dynamical method instead of the one obtained with the thermodynamical method, pointing out the importance of the accurate evaluation of the transition density when studying observational phenomena. We have also studied the moment of inertia of NSs, which is compared to constraints proposed in the literature. Finally, the tidal deformability for NSs is also calculated and compared with the constraints coming from the GW170817 event detected by the LIGO and Virgo observatories and which accounts for the merger of two NSs in a binary system.El coneixement de l’equació d’estat (EoS) de matèria altament densa i assimètrica és essencial per tal d’estudiar les estrelles de neutrons (NSs). En aquesta tesi s’analitzen, utilitzant interaccions de camp mig no relativistes, les propietats de l’EoS i la seva influència en càlculs de NSs. Primerament, s’estudia la convergència del desenvolupament en sèrie de Taylor de l’EoS en potències de l'assimetria d’isospí. Seguidament, s’analitza l’exactitud dels resultats per matèria β-estable, la qual es troba a l’interior de les NSs, quan es calcula utilitzant el desenvolupament de Taylor de l’EoS. La relació entre la massa i el radi obtinguda integrant les equacions Tolman-Oppenheimer-Volkoff (TOV) també és estudiada. A causa de que les interaccions de Gogny de la família D1 no aconsegueixen donar NSs compatibles amb observacions astrofísiques, en aquesta tesi proposem dues noves forces de Gogny, anomenades D1M∗ i D1M∗∗, les quals poden donar, respectivament, NSs de 2 i 1.91 masses solars. Una altra part de la tesi es dedica a l’estudi de la transició entre l’escorça i el nucli, buscant la densitat a la qual la matèria uniforme al nucli és inestable contra fluctuacions de densitat. Ho estudiem amb dos mètodes, el mètode termodinàmic i el mètode dinàmic. Finalment, s’analitzen diverses propietats de les NSs, com són la relació entre la massa i el radi de l’estrella, les propietats de l’escorça, el moment d’inèrcia, així com la deformació deguda als corrents de marea (tidal deformability) que està relacionada amb l’emissió d’ones gravitacionals en sistemes binaris d’estrelles de neutrons.
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Clark, Michael C. "Bowen-type initial data for simulations of neutron stars in binary systems." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55005.
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A new method for generating initial data for simulations of neutron stars in binary systems. The construction of physically relevant initial data is crucial to accurate assessment of gravitational wave signals relative to theoretical predictions. This method builds upon the Bowen-York curvature for puncture black holes. This data is evolved and compared against simulations in the literature with respect to orbital eccentricity, merger and collapse times, and emitted energy and angular momentum. The data exhibits some defects, including large central density oscillations in stars and center of mass drift in unequal-mass systems. Some approaches for improvements in potential future work are discussed.
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Ashton, Gregory. "Timing variations in neutron stars : models, inference and their implications for gravitational waves." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/401822/.
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Timing variations in pulsars, low frequency ubiquitous structure known as timing noise and sudden increases in the rotational frequency which we call glitches, provide a means to study neutron stars. Since the first observations, many models have been proposed, yet no definitive explanation has arisen. In this thesis, we aim to improve this situation by developing models of timing noise. We focus chiefly on precession models which explain periodic modulation seen in radio pulsar data. Developing models and testing them provides an opportunity to infer the elemental properties of neutron stars: evidence for long period precession has implications for the superfluid component predicted by models used to explain glitches. However, often more than one model can qualitatively explain the data, therefore we need a method to decide which model best fits the data. This is precisely the case for PSR B1828-11 which has been used as evidence for both precession and so-called magnetospheric switching. We address this confusion by applying the tools of probability theory to develop a Bayesian model comparison and find that the evidence is in favour of precession. In the second part of this thesis, we will discuss the implications of timing variations for the detection of continuous gravitational waves from neutron stars. To search for these signals, matched filtering methods are used which require a template, a guess for what the signal ‘looks like’. Timing variations, as seen in the electromagnetic signal, may also exist in the gravitational wave signal. If detected, these could provide an invaluable source of information about neutron stars. However, if not included in the template, they may mean that the gravitational wave signal is not detected in the first place. We investigate this issue for both timing noise and glitches, using electromagnetic observations to predict for what types of gravitational wave searches this may be an issue. We find that while timing noise is unlikely to be an issue for current gravitational wave searches, glitches may cause a significant problem in all-sky searches for gravitational waves from neutron stars.
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Yu, Hoi-fung, and 余海峰. "Gravitational waves from the phase-transition-induced collapse of neutron stars using 2-dimensional general relativistic code." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46604078.
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Pitkin, Matthew David. "Searches for continuous and transient gravitational waves from known neutron stars and their astrophysical implications." Thesis, University of Glasgow, 2006. http://theses.gla.ac.uk/3558/.
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We have used data from the third and fourth science runs of the laser interferometric gravitational wave detectors LIGO and GEO600 to produce upper limits on the emission of gravitational waves from a selection of known neutron stars. Two different emission mechanisms are looked into; i) the emission of continuous gravitational waves from triaxial neutron stars; and ii) emission of quasi-normal mode ring-downs from glitching neutron stars. We have produced upper limits on the gravitational wave amplitude and ellipticity for 93 known pulsars assuming continuous emission via triaxiality. This selection of pulsars includes the majority of currently known pulsars with frequencies > 25 Hz, with many within binary systems and globular clusters. New algorithms to take into account the motions within binary systems and possible effects of pulsar timing noise are presented. Also shown is the first analysis to combine the data sets from two distinct science runs as a method of lowering the upper limits. The results are starting to push into the range of plausible neutron star ellipticities, with the Crab pulsar closely approaching the limit that can be set through spin-down arguments. For the 32 of these pulsars in globular clusters the results provide upper limits independent of the cluster dynamics. The astrophysical significance of these results is discussed. Along with results from true pulsars we also present the extraction of simulated signals injected into the interferometers during the science runs. These provide validation checks of both the extraction software and the coherence of the detectors. Two techniques are discussed in relation to searching for quasi-normal mode ring-down signals from excited neutron stars, for example during a glitch; one based on matched filtering and the other based on Bayesian evidence. These are both applied to a search for such a signal from SGR1806 20 during a GRB on 27th December 2004, using the LIGO H1 detector and GEO600 data. This search provided upper limits on the energy released in gravitational waves via quasi-normal modes over the range of frequencies from 1-4 kHz. These are compared with results from a previous search using the bar detector AURIGA (Baggio et al, 2005) and theoretical arguments. The limitations of the search and search techniques, and possible extensions to these, are discussed. The future of these searches is discussed with regard to extensions to the analysis techniques and number of potential sources. Particular emphasis is placed on searches using data from the current LSC S5 science run.
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Cowperthwaite, P. S., E. Berger, V. A. Villar, B. D. Metzger, M. Nicholl, R. Chornock, P. K. Blanchard, et al. "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626064.
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We present UV, optical, and near-infrared (NIR) photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at 0.47-18.5 days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-South/ FLAMINGOS-2 (GS/F2), and the Hubble Space Telescope (HST). The spectral energy distribution (SED) inferred from this photometry at 0.6 days is well described by a blackbody model with T approximate to 8300 K, a radius of R approximate to 4.5 x 10(14) cm (corresponding to an expansion velocity of v approximate to 0.3c), and a bolometric luminosity of L-bol approximate to 5 x 10(41) erg s(-1). At 1.5 days we find a multi-component SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands and significant reddening of the optical/ NIR colors. Modeling the entire data set, we find that models with heating from radioactive decay of Ni-56, or those with only a single component of opacity from r-process elements, fail to capture the rapid optical decline and red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data; the resulting "blue" component has M-ej(blue) approximate to 0.01 M-circle dot and v(ej)(blue) approximate to 0.3c, and the "red" component has M-cj(red) approximate to 0.04 M-circle dot and v(cj)(red) approximate to 0.1 c. These ejecta masses are broadly consistent with the estimated r-process production rate required to explain the Milky Way r-process abundances, providing the first evidence that binary neutron star (BNS) mergers can be a dominant site of r-process enrichment.
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Soares-Santos, M., R. Kessler, E. Berger, J. Annis, D. Brout, E. Buckley-Geer, H. Chen, et al. "A DARK ENERGY CAMERA SEARCH FOR AN OPTICAL COUNTERPART TO THE FIRST ADVANCED LIGO GRAVITATIONAL WAVE EVENT GW150914." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621228.
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We report the results of a deep search for an optical counterpart to the gravitational wave (GW) event GW150914, the first trigger from the Advanced LIGO GW detectors. We used the Dark Energy Camera (DECam) to image a 102 deg(2) area, corresponding to 38% of the initial trigger high-probability sky region and to 11% of the revised high-probability region. We observed in the i and z bands at 4-5, 7, and 24 days after the trigger. The median 5 sigma point-source limiting magnitudes of our search images are i = 22.5 and z = 21.8 mag. We processed the images through a difference-imaging pipeline using templates from pre-existing Dark Energy Survey data and publicly available DECam data. Due to missing template observations and other losses, our effective search area subtends 40 deg(2), corresponding to a 12% total probability in the initial map and 3% in the final map. In this area, we search for objects that decline significantly between days 4-5 and day 7, and are undetectable by day 24, finding none to typical magnitude limits of i = 21.5, 21.1, 20.1 for object colors (i - z) = 1, 0, - 1, respectively. Our search demonstrates the feasibility of a dedicated search program with DECam and bodes well for future research in this emerging field.
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Cowperthwaite, P. S., E. Berger, M. Soares-Santos, J. Annis, D. Brout, D. A. Brown, E. Buckley-Geer, et al. "A DECAM SEARCH FOR AN OPTICAL COUNTERPART TO THE LIGO GRAVITATIONAL-WAVE EVENT GW151226." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621399.
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We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg(2) of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2-24 days after the GW detection. We achieve 5 sigma point-source limiting magnitudes of i approximate to 21.7 and z approximate to 21.5, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with greater than or similar to 3 sigma significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of i - z approximate to 0.3 mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations.
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Ewings, Russell A. "Neutron and X-ray scattering studies of strongly correlated electron systems." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489436.
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In this thesis results of x-ray scattering and neutron scattering experiments on several strongly correlated transition metal oxides are presented. The prototypical charge ordered cuprate La1.48Nd0.4Sr0.12CuO4 was investigated using polarised neutron scattering. The results show that several proposed schemes for the magnetic order in this class of materials may be ruled out, however the data are consistent with one-dimensional stripe-like magnetic order. X-ray diffraction was used to show that the charge order is insensitive to an applied magnetic field, but might be affected by the existence of superconductivity. The magnetic excitations were also studied, and at low energies a gap in the magnetic fluctuations was observed and there is tentative evidence that this is related to magnetic anisotropy. The spin state transition in LaCoO3 was investigated using neutron inelastic scattering, and excitations reminiscent of those observed in ferromagnets above their critical temperatures were observed. The debate surrounding the nature of the excited spin state, S=1 or S=2, could not be resolved, however. The nature of the spin excitations in La0.82Sr0.18CoO3 was investigated using polarised neutrons and it was found that at low energies the excitations take the form of spin-waves. At higher energies this mode becomes heavily damped, and several possible damping mechanisms for this are discussed. Finally, the multiferroic material DyMn2O5 was studied using x-ray resonant scattering. A complex, temperature dependent, magnetic structure was found using a Dy resonance, which reflects an underlying order of the Mn ions. The measurements were in agreement with a theory of multiferroics based on acentric spin-density waves.
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Dudi, Reetika [Verfasser], Bernd [Gutachter] Brügmann, John [Gutachter] Veitch, and Ajith [Gutachter] Parameswaran. "Gravitational waves from binary neutron stars systems / Reetika Dudi ; Gutachter: Bernd Brügmann, John Veitch, Ajith Parameswaran." Jena : Friedrich-Schiller-Universität Jena, 2020. http://d-nb.info/122118475X/34.
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Bouffanais, Yann. "Bayesian inference for compact binary sources of gravitational waves." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC197/document.
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La première détection des ondes gravitationnelles en 2015 a ouvert un nouveau plan d'étude pour l'astrophysique des étoiles binaires compactes. En utilisant les données des détections faites par les détecteurs terrestres advanced LIGO et advanced Virgo, il est possible de contraindre les paramètres physiques de ces systèmes avec une analyse Bayésienne et ainsi approfondir notre connaissance physique des étoiles binaires compactes. Cependant, pour pouvoir être en mesure d'obtenir de tels résultats, il est essentiel d’avoir des algorithmes performants à la fois pour trouver les signaux de ces ondes gravitationnelles et pour l'estimation de paramètres. Le travail de cette thèse a ainsi été centré autour du développement d’algorithmes performants et adaptées au problème physique à la fois de la détection et de l'estimation des paramètres pour les ondes gravitationnelles. La plus grande partie de ce travail de thèse a ainsi été dédiée à l'implémentation d’un algorithme de type Hamiltonian Monte Carlo adapté à l'estimation de paramètres pour les signaux d’ondes gravitationnelles émises par des binaires compactes formées de deux étoiles à neutrons. L'algorithme développé a été testé sur une sélection de sources et a été capable de fournir de meilleures performances que d'autres algorithmes de type MCMC comme l'algorithme de Metropolis-Hasting et l'algorithme à évolution différentielle. L'implémentation d'un tel algorithme dans les pipelines d’analyse de données de la collaboration pourrait augmenter grandement l'efficacité de l'estimation de paramètres. De plus, il permettrait également de réduire drastiquement le temps de calcul nécessaire, ce qui est un facteur essentiel pour le futur où de nombreuses détections sont attendues. Un autre aspect de ce travail de thèse a été dédié à l'implémentation d'un algorithme de recherche de signaux gravitationnelles pour les binaires compactes monochromatiques qui seront observées par la future mission spatiale LISA. L'algorithme est une mixture de plusieurs algorithmes évolutionnistes, avec notamment l'inclusion d'un algorithme de Particle Swarm Optimisation. Cette algorithme a été testé dans plusieurs cas tests et a été capable de trouver toutes les sources gravitationnelles comprises dans un signal donné. De plus, l'algorithme a également été capable d'identifier des sources sur une bande de fréquence aussi grande que 1 mHz, ce qui n'avait pas été réalisé au moment de cette étude de thèseThe first detection of gravitational waves in 2015 has opened a new window for the study of the astrophysics of compact binaries. Thanks to the data taken by the ground-based detectors advanced LIGO and advanced Virgo, it is now possible to constrain the physical parameters of compact binaries using a full Bayesian analysis in order to increase our physical knowledge on compact binaries. However, in order to be able to perform such analysis, it is essential to have efficient algorithms both to search for the signals and for parameter estimation. The main part of this thesis has been dedicated to the implementation of a Hamiltonian Monte Carlo algorithm suited for the parameter estimation of gravitational waves emitted by compact binaries composed of neutron stars. The algorithm has been tested on a selection of sources and has been able to produce better performances than other types of MCMC methods such as Metropolis-Hastings and Differential Evolution Monte Carlo. The implementation of the HMC algorithm in the data analysis pipelines of the Ligo/Virgo collaboration could greatly increase the efficiency of parameter estimation. In addition, it could also drastically reduce the computation time associated to the parameter estimation of such sources of gravitational waves, which will be of particular interest in the near future when there will many detections by the ground-based network of gravitational wave detectors. Another aspect of this work was dedicated to the implementation of a search algorithm for gravitational wave signals emitted by monochromatic compact binaries as observed by the space-based detector LISA. The developed algorithm is a mixture of several evolutionary algorithms, including Particle Swarm Optimisation. This algorithm has been tested on several test cases and has been able to find all the sources buried in a signal. Furthermore, the algorithm has been able to find the sources on a band of frequency as large as 1 mHz which wasn’t done at the time of this thesis study
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Kawaguchi, Kyohei. "Black Hole-Neutron Star Merger -Effect of Black Hole Spin Orientation and Dependence of Kilonova/Macronova-." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225394.
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Souza, Gibran Henrique de 1989. "Oscilações da crosta em estrelas de nêutrons magnetizadas e a validade das relações universais para o modo fundamental das ondas gravitacionais." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/330797.
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Orientadores: Cecilia Bertoni Martha Hadler Chirenti, Ernesto KempTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-09-03T00:23:17Z (GMT). No. of bitstreams: 1 Souza_GibranHenriqueDe_D.pdf: 9537099 bytes, checksum: 8b4790f32975067863cff845c7c37170 (MD5) Previous issue date: 2017
Resumo: No presente trabalho focamos na descrição das oscilações da crosta de estrelas de nêutrons que apresentam um campo magnético poloidal com uma componente toroidal, onde utilizamos de oito equações de estado para descrever a matéria constituinte destas estrelas de nêutrons. Para isso apresentamos todo o formalismo matemático para descrever a estrutura interna, rotação, campo magnético e perturbações no fluido necessário para a apresentação dos resultados obtidos. Paralelo a isso efetuamos a extensão dos resultados obtidos na dissertação de mestrado, onde foi apresentado o cálculo das características das ondas gravitacionais do modo-f, como frequência de oscilação e tempo de decaimento. Aqui estendemos os resultados anteriormente obtidos com a inclusão de novas equações de estado e o teste da validade das chamadas relações universais
Abstract: In the present work we focus on the description of the crustal oscillations of neutron stars that present a poloidal magnetic field with a toroidal component, where we use eight equations of state to describe the constituent matter of these neutron stars. For this, we developed all the mathematical formalism to describe the internal structure, rotation, magnetic field and perturbations in the fluid necessary for the presentation of the obtained results. Parallel to this, we extended the results obtained in the student's master dissertation, where the calculation of the characteristics of the f-mode gravitational waves was presented, such as oscillation frequency and decay time. Here we extend the previously obtained results with the inclusion of new state equations and the test of the validity of the so-called universal relations
Doutorado
Física
Doutor em Ciências
140838/2013-9
CNPQ
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Behnke, Berit [Verfasser]. "A directed search for continuous gravitational waves from unknown isolated neutron stars at the galactic center / Berit Behnke." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1042065853/34.
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Souza, Gibran Henrique de 1989. "O modo fundamental de emissão de ondas gravitacionais." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277493.
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Orientadores: Anderson Campos Fauth, Cecilia Bertoni Martha Hadler ChirentiDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Usando como base um código computacional que integra numericamente as equações TOV, que descrevem o interior de corpos relativísticos de simetria esférica, com a equação de estado SLy, que fornece a pressão em função da densidade para a matéria nuclear em condições extremas se comparadas à matéria nuclear convencional, conseguimos descrever uma estrela de nêutrons realista e com esta simular a emissão de ondas gravitacionais, com a previsão de como seria seu tempo de decaimento e frequência
Abstract: Using as base a computer code that integrates numerically the TOV equations, which describe the interior of relativistic bodies of spherical symmetry, with the SLy equation of state, which provides the pressure in function of density for nuclear matter under extreme conditions when compared with conventional nuclear matter, we describe a realistic neutron star and simulate the emission of gravitational waves, with the predictions of how its decay rate and frequency will be
Mestrado
Física
Mestre em Física
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Singh, Avneet [Verfasser], and Maria Alessandra [Akademischer Betreuer] Papa. "Improved post-processing in searches for continuous gravitational waves and a model for transient continuous gravitational wave emission from neutron star glitches / Avneet Singh ; Betreuer: Maria Alessandra Papa." Hannover : Gottfried Wilhelm Leibniz Universität, 2018. http://d-nb.info/1161845429/34.
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Cratere, Angela. "Prospects for future observations of off-axis short gamma-ray burst jets associated with binary neutron star mergers." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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In this thesis work, I assess the short- and long-term prospects for the joint detection of BNSs and SGRBs with next-generation γ-ray and GW detectors. I combine the Structured Jet (SJ) model developed by Salafia et al. (2015b; 2019) for SGRB prompt emission with the analytical model by Finn and Chernoff (1993) for the GW signal from the BNS inspiral phase and estimate future GW-SGRB joint detection rates, using the SJ profile inferred for GRB 170817A (Ghirlanda et al., 2019) and assuming that all BNS mergers can in principle produce a SGRB. I show that, despite the strong assumptions and simplifications of the adopted model, it provides realistic and consistent estimates of the detection rates of SGRBs and GWs obtained with current facilities, the Fermi/GBM and Swift/Burst Alert Telescope γ-ray detectors and the aLIGO O3a GW interferometer. I also show that, if the SJ profile of GRB 170817A is a relatively common feature of SGRBs, then there is no realistic probability of another coincident detection in the era of aLIGO at design sensitivity (i.e., when it has reached the best achievable sensitivity, the project sensitivity) and SVOM-type detectors. In the CE era, the expected rate of coincident SGRB prompt emission and GW signal detections is ≈ 21-22 yr−1 and ≈ 53-55 yr−1 for SVOM-like and THESEUS-like detectors, respectively. I discuss future prospects for this model, showing how future SGRB-GW joint detection can help to solve the tension on the Hubble parameter estimation and to provide tighter constraints on the NS EoS.
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Peralta, Carlos Andrés. "Superfluid spherical Couette flow and rotational irregularities in pulsars /." Connect to thesis, 2006. http://eprints.unimelb.edu.au/archive/00003176.
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Lim, Hyun. "Dynamical Compact Objects in Numerical Relativity." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7729.
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The work of this dissertation will study various aspects of the dynamics of compact objects using numerical simulations.We consider BH dynamics within two modified or alternative theories of gravity. Within a family of Einstein-Maxwell-Dilaton-Axion theories, we find that the GW waveforms from binary black hole (BBH) mergers differ from the standard GW waveform prediction of GR for especially large axion values. For more astrophysically realistic (i.e. smaller) values, the differences become negligible and undetectable. Weestablish the existence of a well-posed initial value problem for a second alternative theory fo gravity (quadratic gravity) and demonstrate in spherical symmetry that a linear instability is effectively removed on consideration of the full nonlinear theory.We describe the key components and development of a code for studying BBH mergers for which the mass ratio of the binaries is not close to one. Such intermediate mass ratio inspirals (IMRIs) are much more difficult to simulate and present greater demands on resolution, distributed computing, accuracy and efficiency. To this end, we present a highly-scalable framework that combines a parallel octree-refined adaptive mesh with a wavelet adaptive multiresolution approach. We give results for IMRIs with mass ratios up to 100:1. We study the ejecta from BNS in Newtonian gravity. Using smoothed particle hydrodynamics we develop and present the highly scalable FleCSPH code to simulate such mergers. As part of the ejecta analysis, we consider these mergers and their aftermath as prime candidates for heavy element creation and calculate r-process nucleosynthesis within the post-merger ejecta. Lastly we consider a non-standard, yet increasingly explored, interaction between a BH and a NS that serves as a toy model for primordial black holes (PBH) and their possible role as dark matter candidates. We present results from a study of such systems in which a small BH forms at the center of a NS. Evolving the spherically symmetric system in full GR, we follow the complete dynamics as the small BH consumes the NS from within. Using numerical simulations, we examine the time scale for the NS to collapse into the PBH and show that essentially nothing remains behind. As a result, and in contradiction to other claims in the literature, we conclude that thisis an unlikely site for ejecta and nucleosynthesis, at least in spherical symmetry.
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Vajente, Gabriele. "Analysis of sensitivity and noise sources for the Virgo gravitational wave interferometer." Doctoral thesis, Scuola Normale Superiore, 2008. http://hdl.handle.net/11384/85869.
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Harries, Nicholas. "Probing supernova shock waves via neutrino oscillations." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490069.
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The time dependent neutrino oscillation signals due to the passage of a shock wave through the supernovae are analyzed for the case of three active neutrinos and also for the case that there are two additional sterile neutrinos. I re-examine the Landau-Zenner formula, which gives the level crossing probability at a MSW resonance, probing the deviations with specific application to the supernova shock wave. I use these results to examine phase effects which could be present due to multiple resonance crossings at the forward and reverse shocks.
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Jacobson, David. "Spectral modulation, gravity and time-dependent correlations in neutron interferometry /." free to MU campus, to others for purchase, 1996. http://wwwlib.umi.com/cr/mo/fullcit?p9720550.
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Lake, Alysia C. I. "Neutron scattering studies of alternating chain antiferromagnets." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360395.
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Brown, Andrew Simon. "Copolyelectrolyte monolayers : organisation and surface wave dynamics." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4970/.
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The organisation and dynamic behaviour of a copolyelectrolyte monolayer is discussed A linear diblock copolymer of poly(methyl methacrylate) (PMMA) and poly(4-viny ethylpyridinium bromide) (QP4VP) has been the main focus of the study, although films of both the unquaternised copolymer, PMMA-P4VP and a PMMA homopolymei have also been examined for comparative purposes. The polymers were spread or subphases of water and potassium chloride solutions of varying concentrations to determine changes in structure and dynamics with polymer surface concentration and subphase salt concentration. Monolayer behaviour has been characterised from surface pressure isotherms and the use of Brewster angle microscopy. It has been demonstrated that the shape of the isotherm is dependent on the potassium chloride concentration of the subphase. Information on the organisation of the system has been determined by neutron reflectometry. A systematic variation in organisation occurs as both polymer surface concentration and subphase potassium chloride concentration change. The polyelectrolytic QP4VP block stretches more into the subphase with increasing surface concentration or decreasing salt concentration. The results have been compared to scaling laws for polymer brushes. Dynamic behaviour has been studied by the use of surface quasi-elastic light scattering (SQELS) and resonance between the capillary and dilational waves of the system is observed. The phenomenon of mode mixing and the application of viscoelastic models to the system have also been examined. It has been discovered that an accurate description of the surface viscoelastic properties of the system could not be obtained by the use of standard viscoelastic models. Mode mixing was not observed, even in those systems where negative dilational viscosities were found.
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Cross, Brian. "Structure and break-up of one-neutron halo nuclei." Thesis, University of Surrey, 1995. http://epubs.surrey.ac.uk/843872/.
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This thesis concerns the use of nuclear reactions to study the structure of neutron-rich light nuclei. Emphasis is placed on 11Be which has been identified as a nucleus with a single neutron halo and which offers a simple 2-body case for detailed analysis. Comparisons are made with experimental data for the break-up of 11Be on gold, titanium and beryllium targets. As a prelude to more detailed work a simple elastic break-up model calculation, using the Distorted Wave Born Approximation (DWBA), is attempted. The resulting theoretical cross-sections show good agreement with the shape of the experimental data but cannot predict the absolute magnitude. A major part of the break-up work is a more accurate model using the post-form DWBA. The formulation is built up from basic scattering theory and includes details of employing the Zero Range Approximation and the Vincent and Fortune method of integration. A Finite Range Correction is also applied. Cross-section calculations for a gold target agree closely with experiment but a problem arises for lighter targets. Here the Coulomb potential must be excluded from the calculation to obtain a result that matches the experimental data. A method for the calculation of inelastic break-up is presented which only requires a small modification to the methods used for elastic break-up. As it suffers from the same light target problem only calculations for a gold target give an inclusive cross-section, produced from the elastic and inelastic contributions, which matches the experimental data satisfactorily. To overcome the light target problem a full recoil calculation is introduced. Arguments and analysis are produced to show that this method is too demanding of both computing time and storage for practicable implementation. Future calculations are proposed using an analytical method for Coulomb break-up.
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MESSINA, FRANCESCO. "IMPROVING THE EOB TOOLBOX FOR GRAVITATIONAL WAVE DATA ANALYSIS." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/299793.
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La stima dei parametri fisici degli eventi di onde gravitazionali rilevati da LIGO e Virgo si basa su modelli di forme d'onda analitiche, eventualmente calibrati da simulazioni di Relatività Numerica. Il modello EOB (Effective-One-Body) è uno dei principali modelli analitici per l’analisi dei segnali gravitazionali emessi da buchi neri e stelle di neutroni. La qui presente tesi, a grandi linee, è un lavoro di “potenziamento” di questo modello, e in particolare I) lo miglioriamo nei suoi vari settori, con l'obiettivo finale di costruire un modello che includa tutte le informazioni fisiche disponibili: in particolare, quelle riguardanti i multipoli subdominanti, utili per ottimizzare la risoluzione angolare dell'analisi dati degli esperimenti di onde gravitazionali [ 1, 4, 5, 7]; II) usarlo per sviluppare approssimanti Post-Newtoniani veloci, di ordine elevato, molto utili per le analisi bayesiane inerenti le pipeline LIGO e Virgo [3]; III) utilizzarlo per studiare, nel caso delle stelle binarie di neutroni, l’influenza degli effetti di self-spin sulla loro forma d'onda [2].
Uno degli elementi costitutivi centrali del modello EOB è la forma d'onda multipolare Post-Newtoniana (PN) fattorizzata e circolarizzata introdotta in [8] per binarie senza spin. In[4], estendiamo fino a l= 6 (cioè a multipoli alti) l'approccio di Nagar e Shah [9], poiché ha un accordo con la relatività numerica (utilizzata come punto di riferimento per la calibrazione) migliore del suo precursore [8]. In [4], questo approccio è stato aggiornato al caso di una particella rotante intorno ad un buco nero di Schwartzschild. Lo stesso approccio è stato altresì adattato in [5] al fine di aggiornare il modello EOB quadrupolare TEOBResumS, un codice C ++ [1] disponibile nella LIGO Advanced Library (LAL) e citato nel catalogo [10], a una sua naturale versione multipolare [7].
Fatto salvo ciò, mediante la tecnica di espansione EOB-PN definita in [11], il lavoro svolto in [3] conduce a un approssimante fenomenologico di ordine 5.5PN veloce e preciso che, includendo più informazioni sulle correzioni test-particle rispetto a quello standard a 3.5PN, ottimizza la stima dei parametri di marea dell'analisi dei dati BNS. Nel lavoro [2], incorporiamo in TEOBResumS i termini di self-spin dipendenti dall’equazione di stato (EOS) all'ordine next-to-next-to-leading (NNLO), insieme ad altri effetti (bilineari, cubici e quartici) al leading-order (LO). Qui, con la stessa cassetta degli attrezzi usata in[3], studiamo la dipendenza degli effetti di self spin legati all’EOS, e dimostriamo che le correzioni di ordine NLO e NNLO, a livello di interazione monopolo-quadrupolo, producono effetti di accelerazione di fase più marcati rispetto al corrispondente contributo LO; oltre a questo, si osserva altresì che una volta inclusi gli effetti di auto spin al NLO (3PN) nel Taylor F2, essi sono più attrattivi rispetto a quanto previsto dalla corrispondente descrizione EOB. Infine, abbiamo ottenuto un approssimante TaylorF2 che fornisce una rappresentazione analiticamente semplificata, ma fedele all'EOB, degli effetti di self-spin (effetti di coda inclusi) che può essere utile per migliorare gli attuali modelli di forma d'onda PN (o fenomenologici) per l’inspiralling di stelle di neutroni.
Referenze:
References:
[1] Phys. Rev., D98(10):104052, 2018.
[2] Phys. Rev., D99:044007, 2019.
[3] Phys. Rev., D99:124051, 2019.
[4] Phys. Rev., D97(8): 084016, 2018.
[5] Phys. Rev., D100(10):104056, 2019.
[6] Phys. Rev., D99(4):044051, 2019.
[7] Phys. Rev. D 102, 024077 (2020)
[8]Phys. Rev., D79:064004, 2009.
[9] Phys. Rev., D94(10):104017, 2016.
[10] Phys. Rev. X 9, 031040
[11] Phys. Rev., D95(12):124001, 2017.The parameter estimation of gravitational wave events detected by LIGO and Virgo relies on analytical waveforms models, possibly calibrated (or informed) by Numerical Relativity simulations. The effective-one-body (EOB) model is one of the main analytical models available that can be efficiently used for analyzing both black hole and neutron star binaries. In this script we I) improve it in its various sectors, with the final aim to build a model that includes all the physical information available: in particular, the higher subdominant multipoles information, that is useful to optimize GW data analysis’ angular resolution [1, 4, 5, 7]; II) use it to develop high-order fast PN approximants for Bayesian analysis in LIGO and Virgo pipelines [3]; III) use it to study the self-spin effects of binary Neutron Stars on their own waveform [2]. One of the central building blocks of the EOB model is the factorized and resummed (circularized) multipolar post-Newtonian (PN) waveform introduced in Ref. [8] for nonspinning binaries. In Ref. [4], we extend up to ` = 6 (i.e. to high multipoles) the resummation approach of Nagar and Shah [9], since it has a better analytical/numerical relativity agreement than its precursor [8]. Ref. [4], updated to the case of a spinning particle of Schwartzschild problem in Ref. [5], has been used in order to update the spin-aligned, quadrupolar EOB model TEOBResumS, a C++ code [1] available in the LIGO Advanced Library (LAL) and cited in the GW catalogue [10], to a multipolar version [7]. Therefore, following the EOB-PN expansion technique defined in [11], Ref. [3] leads to a fast and accurate 5.5PN phenomenological approximant that, by including more point-mass information than the standard 3.5PN one, optimizes the tidal-parameter estimation of BNS data analysis. In Ref [2], we incorporate the EOS-dependent selfspin terms in TEOBResumS at next-to-next-to-leading (NNLO) order, together with other (bilinear, cubic and quartic) nonlinear-in-spin effects (at leading order, LO). Here, with the same toolbox used in Ref. [3], we study the EOS dependence of the self-spin effects and show that the next-to-leading order (NLO) and NNLO monopole-quadrupole corrections yield increasingly phase-accelerating effects compared to the corresponding LO contribution; that the standard TaylorF2 post-Newtonian (PN) treatment of NLO (3PN) EOS-dependent self-spin effects makes their action stronger than the corresponding EOB description; and, finally, we obtain a tail-augmented TaylorF2 approximant that yields an analytically simplified, EOB-faithful, representation of the EOS-dependent self-spin phasing that can be useful to improve current PN-based (or phenomenological) waveform models for inspiralling neutron star binaries. References: [1] Phys. Rev., D98(10):104052, 2018. [2] Phys. Rev., D99:044007, 2019. [3] Phys. Rev., D99:124051, 2019. [4] Phys. Rev., D97(8): 084016, 2018. [5] Phys. Rev., D100(10):104056, 2019. [6] Phys. Rev., D99(4):044051, 2019. [7] Phys. Rev. D 102, 024077 (2020) [8]Phys. Rev., D79:064004, 2009. [9] Phys. Rev., D94(10):104017, 2016. [10] Phys. Rev. X 9, 031040 [11] Phys. Rev., D95(12):124001, 2017.
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Al, Mamun Md Abdullah. "Nuclei, Nucleons and Quarks in Astrophysical Phenomena." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461.
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BARBIERI, CLAUDIO. "Electromagnetic counterparts of double neutron star and black hole-neutron star binary mergers." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/299795.
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Questa tesi di dottorato è focalizzata sulle controparti elettromagnetiche (EM) dei segnali di onde gravitazionali (GW) generati dai merger di sistemi di due stelle di neutroni (NSNS) e sistemi buco nero-stella di neutroni (BHNS).
Ho sviluppato dei modelli semi-analitici per prevedere l’emissione a varie lunghezze d’onda dai merger di BHNS, includendo la kilonova, il suo radio remnant, la prompt emission del getto relativistico e il seguente gamma-ray burst (GRB) afterglow. Adottando delle formule di fit dalla letteratura, ho stabilito un legame tra i parametri della binaria e le proprietà delle controparti EM.
Ho anticipato la varietà e l’alto grado di degenerazione delle controparti EM dai merger di BHNS. Ho mostrato come l’analisi congiunta GW+EM può ridurre questa degenerazione, eseguendo un esperimento concettuale di stima dei parametri multi-messaggera, considerando un merger BHNS con una kilonova associata. I miei risultati indicano che l’analisi congiunta può produrre migliore informazione sui parametri della binaria. Ciò porterebbe ad una maggiore comprensione della fisica fondamentale delle stelle di neutroni e dei buchi neri (ad esempio l’equazione di stato e la massa massima delle stelle di neutroni, la distribuzione di spin dei buchi neri) e darebbe informazioni sulla formazione ed evoluzione delle binarie di oggetti compatti.
Ho analizzato i merger “ambigui” di binarie (ossia consistenti sia con NSNS che BHNS), la cui natura potrebbe non essere identificata attraverso il solo segnale gravitazionale. Nel caso BHNS, la binaria ospiterebbe un BH stellare “leggero”, la cui massa cadrebbe nella discontinuità tra le masse di stelle di neutroni e buchi neri (mass-gap) attesa teoricamente e ad oggi confermata osservativamente. Ho trovato che l’osservazione della kilonova associata potrebbe svelare la natura del sistema, poiché nel caso BHNS può essere molto più luminosa rispetto al caso NSNS.
Applicando questa analisi all’evento GW190425, ho trovato che la kilonova sarebbe stata osservabile se la binaria avesse ospitato un buco nero (e se la sorgente fosse stata localizzata in cielo con precisione). Ciò avrebbe permesso potenzialmente di identificare la natura del sistema in coalescenza. L’osservazione di una kilonova da un evento “ambiguo” consistente con la natura BHNS sarebbe il primo indizio dell’esistenza di buchi neri stellari “leggeri”, confutando il mass-gap. Ciò fornirebbe nuove informazioni sulla massa massima delle stelle di neutroni e sulla loro equazione di stato, e avrebbe un forte impatto sui modelli di esplosione di supernova, favorendo quelli che producono uno spettro continuo per la massa dei relitti.
Ho presentato un metodo per ottimizzare le campagne di follow-up EM, basato sulla conoscenza della massa di chirp del sistema. Con questa informazione, le configurazioni NSNS e BHNS compatibili possono essere ottenute ed il range atteso di curve di luce di kilonova in diverse bande può essere calcolato. La probabilità di osservare la controparte EM di un evento GW potrebbe essere aumentata se fosse data priorità al follow-up fotometrico e/o spettroscopico dei transienti che risultato consistenti alla loro prima osservazione con il range di kilonova atteso.
Infine ho studiato le probabili distribuzioni delle proprietà EM dei merger NSNS e BHNS che saranno osservati in futuro con le onde gravitazionali. Ciò potrebbe rappresentare un ulteriore utile contributo per l’organizzazione della strategia di follow-up.This PhD dissertation is focused on the electromagnetic (EM) counterparts of gravitational waves (GW) signals from double neutron star (NSNS) and black hole-neutron star (BHNS) mergers. I developed semi-analytical models to predict the multi-wavelength emission from BHNS mergers, including the kilonova, its radio remnant, the prompt emission from the relativistic jet and the related gamma-ray burst (GRB) afterglow. Adopting fitting formulae in the literature, I established a link between the binary parameters and the EM counterparts properties. I anticipated the variety and the high degree of degeneracy of EM counterparts from BHNS mergers. I showed how joint GW+EM analysis can reduce this degeneracy, performing a proof-of-concept multi-messenger parameter estimation, considering a BHNS merger with an associated kilonova. My results indicate that joint analysis can produce better constraints on the binary parameters. This would lead to a deeper understanding of the NS and BH fundamental physics (e.g. the NS equation of state and maximum mass, the BH spin distribution) and would give information on the formation and evolution of compact object binaries. I analyzed “ambiguous” coalescing binaries (consistent with both NSNS and BHNS), whose nature may not be identified through the GW signal alone. In the BHNS case, the binary would host a “light'' stellar BH, with the mass falling in the theoretically expected and to date observationally confirmed discontinuity between NS and BH mass distributions (mass-gap). I found that the observation of the associated kilonova could unveil the system’s nature, as in the BHNS case it can be far more luminous with respect to the NSNS case. Applying this analysis to the GW190425 event, I found that the kilonova would have been detectable if the binary had hosted a BH (if the source had been precisely localized), potentially disentangling the nature of the merging system. The observation of a kilonova from an “ambiguous'' event consistent with a BHNS nature would be the first hint of the existence of “light” stellar BHs, confuting the mass-gap. This would provide new constraints on the NS maximum mass and equation of state, and it would strongly impact the supernova explosion models, favoring those producing a continuum spectrum of remnant masses. I presented a method to optimize the EM follow-up campaigns, based on the knowledge of the system's chirp mass. With this information, the compatible NSNS and BHNS configurations can be obtained and the expected ranges of kilonova light curves in different bands can be computed. The probability of detecting the EM counterpart of a GW event could be enhanced if the observation of transients consistent at their first detection with the expected kilonova ranges was prioritized for photometric and/or spectroscopic follow-up. Finally I studied the EM counterparts properties distributions of future NSNS and BHNS mergers detected with gravitational waves. This could represent another useful contribution for EM follow-up strategy organization.
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Van, Greunen Corneluis Erasmus. "Neutral-point-clamped shunt active filter." Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1265.
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Faber, Joshua Aaron 1977. "Gravity wave signals from relativistic calculations of binary neutron star coalescence." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8283.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.Includes bibliographical references (p. 153-162).
This thesis describes the design, testing, and implementation of a Lagrangian, post-Newtonian, smoothed particle hydrodynamics code used to study the gravitational wave signature produced by coalescing neutron star binary systems. Additionally, we have studied the properties of remnants which may be formed during the merger process. We have introduced a hybrid post-Newtonian formalism, which treats lowest order 1PN relativistic terms at a reduced strength, to make the problem numerically tractable, while treating the gravitational radiation reaction, which is the lowest order dissipative term in general relativity, at full strength. We compare the results of calculations with and without 1PN effects for initially synchronized binary systems, for neutron stars with polytropic equations of state, finding that relativistic corrections play an important role in the dynamical stability of such sytems and the resulting gravitational wave forms. Relativistic corrections also suppress mass shedding in these systems. Studies of initially irrotational binary systems demonstrated that our results are independent of the numerical resolution of the calculations. The power spectrum of the gravitational radiation produced during a merger is found to yield important information about the neutron star equation of state, the binary mass ratio, and other physical parameters of the system.
by Joshua Aaron Faber.
Ph.D.
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Hotokezaka, Kenta. "Theoretical study of signals from binary neutron star mergers." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188486.
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Yang, Huan, Vasileios Paschalidis, Kent Yagi, Luis Lehner, Frans Pretorius, and Nicolás Yunes. "Gravitational wave spectroscopy of binary neutron star merger remnants with mode stacking." AMER PHYSICAL SOC, 2018. http://hdl.handle.net/10150/627067.
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A binary neutron star coalescence event has recently been observed for the first time in gravitational waves, and many more detections are expected once current ground-based detectors begin operating at design sensitivity. As in the case of binary black holes, gravitational waves generated by binary neutron stars consist of inspiral, merger, and postmerger components. Detecting the latter is important because it encodes information about the nuclear equation of state in a regime that cannot be probed prior to merger. The postmerger signal, however, can only be expected to be measurable by current detectors for events closer than roughly ten megaparsecs, which given merger rate estimates implies a low probability of observation within the expected lifetime of these detectors. We carry out Monte Carlo simulations showing that the dominant postmerger signal (the l = m = 2 mode) from individual binary neutron star mergers may not have a good chance of observation even with the most sensitive future ground-based gravitational wave detectors proposed so far (the Einstein Telescope and Cosmic Explorer, for certain equations of state, assuming a full year of operation, the latest merger rates, and a detection threshold corresponding to a signal-to-noise ratio of 5). For this reason, we propose two methods that stack the postmerger signal from multiple binary neutron star observations to boost the postmerger detection probability. The first method follows a commonly used practice of multiplying the Bayes factors of individual events. The second method relies on an assumption that the mode phase can be determined from the inspiral waveform, so that coherent mode stacking of the data from different events becomes possible. We find that both methods significantly improve the chances of detecting the dominant postmerger signal, making a detection very likely after a year of observation with Cosmic Explorer for certain equations of state. We also show that in terms of detection, coherent stacking is more efficient in accumulating confidence for the presence of postmerger oscillations in a signal than the first method. Moreover, assuming the postmerger signal is detected with Cosmic Explorer via stacking, we estimate through a Fisher analysis that the peak frequency can be measured to a statistical error of similar to 4-20 Hz for certain equations of state. Such an error corresponds to a neutron star radius measurement to within similar to 15-56 m, a fractional relative error similar to 4%, suggesting that systematic errors from theoretical modeling greater than or similar to 100 m) may dominate the error budget.
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Gaw, Stephen Michael. "Cooperative spin excitations in quantum materials studied by neutron spectroscopy." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c20676e1-b927-4ee5-a3fe-97f0f80cb141.
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This thesis describes the experimental investigation of three different strongly correlated transition-metal oxide systems. The magnetic behaviour of each has been probed using inelastic neutron spectroscopy. A distinctive hour-glass excitation spectrum has been observed in the layered cobaltate La1.75Sr0.25CoO4. This spectrum is similar to that measured in a related cobaltate La1.67Sr0.33CoO4, although it appears broader. The spectrum has been reproduced using a spin wave model derived from a disordered cluster spin glass ground state. Signatures of spin glass behaviour have also been observed in bulk magnetisation measurements of La1.75Sr0.25CoO4. These findings, once more, demonstrate the emergence of an hour-glass spectrum from a ground state that combines quasi-one dimensional magnetic correlations and disorder. Additionally, this study shows that charge and magnetic stripe order persists to lower dopings in La2-xSrxCoO4 than previously thought. The complete magnetic excitation spectrum of the multiferroic compound CuO has been measured for the first time. A high energy, one-dimensional magnetic spectrum is observed and modelled using the Muller ansatz derived for the S=1/2 Heisenberg antiferromagnetic chain. At lower energies, a three-dimension spectrum is observed. The measured spectrum is inconsistent with all previous theoretical estimates of the dominant inter-chain exchange interactions in CuO. The inter-chain dispersion is successfully described by a phenomenological model based on linear spin wave theory. The third material investigated, LuFe2O4 demonstrates complex charge and magnetic order, the precise nature of which is still under debate. The full spectrum of in-plane excitations in LuFe2O4 has been measured and a complicated dispersion consistent with six magnetic modes is observed. These findings are compatible with structures described by a magnetic unit cell containing six spins. The dispersion can be described by a spin wave model derived from a bilayer structure comprised of charge-rich and charge-poor monolayers. This structure is consistent with the original site-specific model for the 3D magnetic ordering in LuFe2O4.
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Paolasini, Luigi. "Etudes par diffusion de neutrons des corrélations et des excitations magnétiques dans les composés intermétalliques UFe2 et UPd2Al3." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10021.
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L'etude des proprietes magnetiques par diffusion inelastique et elastique de neutrons a ete realise sur deux composes intermetalliques de l'uranium: ufe#2 et upd#2al#3. La dynamique des ondes de spin a ete etudiee par diffusion inelastique de neutrons sur le ferromagnetique itinerant ufe#2 (t#c=165k). On a observe une seule onde de spin associee a la precession en phase des spins des atomes du fer, compare aux trois modes a faible energie prevus par le modele lineaire des ondes de spin, valable pour les composes isomorphes des terres rares rfe#2. Un regime hydrodynamique de type diffusif se manifeste autour de la temperature de transition et la valeur de sa constante de raideur depasse celle calculee pour les rfe#2 et le fer pur. Un fort amortissement de la branche acoustique des phonons transverses confirme les mesures des constantes elastiques par la methode ultrasonique. Les etudes par diffusion elastique de neutrons sur le fermion lourd supraconducteur upd#2al#3 (t#c=2k) sont centrees sur les proprietes magnetiques de l'etat normal de ce compose. Les mesures par diffusion de neutrons polarises nous ont permis de determiner la densite d'aimantation dans l'etat paramagnetique et de calculer par l'approximation dipolaire les contributions du moment orbital et de spin des electrons 5f de l'uranium. La structure magnetique a ete determinee par diffraction elastique de neutrons non polarises dans l'etat antiferromagnetique (t#n=15k). La dependance des intensites magnetiques en fonction d'un champ applique dans le plan d'anisotropie nous a permis de determiner l'orientation des moments magnetiques et d'interpreter le diagramme de phase, propose dans la litterature, comme un effet de reorientation des domaines magnetiques. Le dernier chapitre, contenant toute une serie d'experiences sur deux monocristaux de composition nominale differentes, se veut le point de depart de futures etudes sur la structure cristallographique et morphologique des defauts observes dans ces cristaux
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Garg, Vidur. "Swept Neutral Pressure Instrument (SNeuPI): Investigating Gravity Waves In The Ionosphere." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/56592.
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A swept neutral pressure instrument(SNeuPI) is used to study the effect of gravity waves on the composition of the ionosphere. When mounted on a nanosatellite in the low earth orbit, changes in atmospheric pressure due to gravity waves are measured as the changes in neutral gas density. This measurement is achieved by use of micro-tip emitters as an electron source and micro channel plates(MCPs) as ion collectors. Ionization of the neutral gas produces a current at the output of the MCPs to quantify the pressure of the ionosphere. Traditionally, such measurements are made on larger satellites which enable the use of higher power equipment. This thesis describes the design and use of a low power instrument, to be used on a limited-resource satellite. The background and theoretical analysis is presented first, followed by descriptions of the mechanical and electrical designs. The laboratory tests are limited to a vacuum chamber setup that simulates the conditions of the ionosphere.Master of Science
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Ren, Zhensong. "Combined neutron, transport and material based investigation in Ca₃Ir₄Sn₁₃." Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104538.
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Thesis advisor: Stephen D. WilsonThis dissertation investigates the cubic type II superconductor, Ca₃Ir₄Sn₁₃, discovered by Remeika and the coauthors more than 30 years ago. It was originally discovered be to a superconductor and later suggested to host ferromagnetic spin fluctuations, which lead to a peak-like anomaly in thermodynamic and transport measurements. Later detailed x-ray single crystal structural refinement associated the peak-like anomaly in transport and magnetization measurements with a charge density wave phase transition at the same temperature. The potential charge density wave phase transition T* can be suppressed either by pressure or chemical potential through substitution on the Ca and Ir site such that a temperature-pressure/composition phase diagram can be constructed. Upon investigating magnetism in this compound, polarized neutron scattering and μSR data from our group and other researchers did not reveal any magnetic order or magnetic spin fluctuations at the time scale of μSR . However, through the partial substitution of Ir by Rh, we realized a structural quantum critical point at ambient pressure with 30% of Ir substituted by Rh--providing the research community a valuable material's platform for studying the interplay between 3D charge density wave order and superconductivity. On the other hand, our surprising discovery of the weak HHL (L=odd) type of super-lattice peaks from neutron scattering led us to a tentative model of a distorted Ca sublattice in this material. The similarity of the lattice instabilites of the Remeika compound and A15 superconductors are discussed, which may give us more insight into its role in the formation of the superconducting phase
Thesis (PhD) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Güven, Haşim Zahid. "Nuclear Physics in Neutron Stars : Study of Superfluidity in Hypernuclei and Constraining the Nuclear Equation of State." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP041.
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Dans cette thèse nous avons d’abord étudié l’effet du paring Lambda sur les propriétés des hypernoyaux dans le formalisme Hartree-Fock Bogoliubov. La fonctionnelle de Skyrme SLy5 est utilisée dans le canal nucleon-nucleon alors que 3 fonctionelles fittées sur les calculs microscopiques Brueckner Hartree-Fock sont utilisées dans le canal Nλ : DF-NSC89, DF-NSC97a et DF-NSC97f. Ces fonctionnelles décrivent la séquence des énergies de liaison expérimentales à un lambda, des hypernoyaux légers aux hypernoyaux lourds. Dans le cas du canal Lambda-Lambda, nous avons utilisé la prescription empirique EmpC, ajustée à 1 MeV sur l’énergie expérimentale de liaison dans le 6HeLL. A l’aide de cette approche de la fonctionnelle de la densité, plusieurs noyaux ont été étudiés, avec des couches nucléoniques fermées et des couches ouvertes en Lambda. Une interaction d’appariement Lambda-Lambda est introduite, dont la magnitude est ajustée pour être consistante avec la valeur maximale des prédictions BCS pour le gap d’appariement Lambda dans la matière hyperonique. Nous donnons ainsi une valeur maximale pour la prédiction du gap d’appariement Lambda et ses effets dans les hypernoyaux. Nous avons montré que les effets de l’appariement LL dépendent de l’hypernoyau considéré. L’énergie correspondante de condensation est de l’ordre de 3 MeV au maximum, ce qui entraine de faibles corrections sur les distributions de densité et la structure en couches. De manière générale, nous avons trouvé que l’appariement Lambda-Lambda peut être important si l’écart en énergie entre les couches est plus petit que 3 MeV. A cette condition, l’appariement Lambda peut impacter les densité et les énergies de liaison. En résumé, il est montré que l’effet de l’appariement relié aux Lambda peut être en général négligé dans la plupart des hypernoyaux, sauf pour les ceux ayant un écart typique dans le spectre à une particule plus petit que 3 MeV autour du niveau de Fermi. De plus, les conditions sur à la fois les énergies de Fermi et les moments angulaire orbitaux atténuent l’appariement nucleon-Lambda pour la plupart des hypernoyaux.La deuxième partie de la thèse est dévolue aux équations d’état dans les étoiles à neutrons. Nous avons confronté les valeurs des déformabilité de marée extraites de l’évènement d’onde gravitationnelle GW170817, aux contraintes issues de la physique nucléaire à l’aide d’une approche semi-agnostique pour l’équation d’état de la matière dense. Nous avons utilisé les statistiques Bayesienne pour combiner les données de physique nucléaire à basse densité, comme les prédictions ab initio provenant des interactions chirales EFT ou la résonance géante monopolaire isoscalaire, et les contraintes astrophysiques des étoiles à neutrons, comme leur masse maximale, ou la fonction densité de probabilité de la déformabilité de marée obtenue de l’événement GW170817. Les fonctions postérieures de densité de probabilité sont marginalisées sur plusieurs paramètres nucléaires empiriques (Lsym, Ksym, Qsat et Qsym), et aussi sur des grandeurs observationnelles des étoiles à neutrons comme la masse et le rayon à 1.4 masses solaires, ou la pression à deux fois la densité de saturation P(2nsat). Les correlations entre Lsym et Ksym, et entre KSat et Qsat sont aussi analysées. Une tension importante entre les données observationnelles d’ondes gravitationnelles et les inputs de physique nucléaire est trouvée pour les distributions marginales de probabilité de Lsym et R1.4. Ceci pourrait être une indication d’une transition de phase de nucléons vers des particules plus exotiques dans le coeur des étoiles à neutrons. Nous trouvons aussi qu’augmenter la précision sur la détermination de la déformabilité de marée à partir des ondes gravitationnelles, ou sur Mc à partir de la résonance géantes monopolaire, devrait aboutir à une meilleure détermination de Ksat et QsatIn this thesis, we first investigated the effect of Lambda pairing on the ground state properties of hypernuclei within the Hartree-Fock-Bogoliubov formalism. The SLy5 Skyrme functional is used in the NN channel, while for N-Lambda channel we employ three functionals fitted from microscopic Brueckner-Hartree-Fock calculations: DF-NSC89, DF-NSC97a and DF-NSC97f. These functionals reproduce the sequence of single-Lambda experimental binding energies from light to heavy hypernuclei. For the Lambda-Lambda channel, we used the empirical prescription EmpC, calibrated to 1 MeV on the experimental bond energy in 6He_LL. Based on this density-functional approach, several nuclei have been studied with nucleon closed-shells and Lambda open-shells. A Lambda-Lambda pairing interaction is introduced, which magnitude is calibrated to be consistent with the maximum BCS predictions for the Lambda pairing gap in hypernuclear matter. In this way, we provide an upper bound for the prediction of the Lambda pairing gap and its effects in hypernuclei. We have shown that the effects of the Lambda-Lambda pairing depends on hypernuclei. The condensation energy is predicted to be about 3~MeV as a maximum value, yielding small corrections on density distributions and shell structure. Generally, we found that Lambda-Lambda pairing could be active if the energy gap between shells is smaller than 3~MeV. Under this condition, Lambda pairing could impact densities and binding energies. Since only a weak spin-orbit interaction is expected in the Lambda channel, Lambda states are highly degenerated and usually levels are distant by more than 3~MeV in energy. In summary, it is shown that the Lambda-related pairing effect can usually be neglected in most of hypernuclei, except for hypernuclei which have a single particle gap lower than 3~MeV around the Fermi level. In addition, conditions on both Fermi energies and orbital angular momenta are expected to quench the nucleon-Lambda pairing for most of hypernuclei.The second part of the thesis is devoted to equation of states in neutron stars. We confronted the tidal deformability values extracted from the gravitational event GW170817 to nuclear physics constraints within a semi-agnostic approach for the dense matter equation of state. We used Bayesian statistics to combine together low density nuclear physics data, such as the ab-initio predictions based on chiral EFT interactions or the isoscalar giant monopole resonance, and astrophysical constraints from neutron stars, such as the maximum mass of neutron stars or the probability density function of the tidal deformability obtained from the GW170817 event. The posteriors probability distribution functions are marginalized over several nuclear empirical parameters (Lsym, Ksym, Qsat and Qsym), as well as over observational quantities such as the 1.4Msun radius R1.4 and the pressure at twice the saturation density P(2n_sat). The correlations between Lsym and Ksym and between Ksat and Qsat are also further analyzed. It is found that there is a marked tension between the gravitational wave observational data and the nuclear physics inputs for the Lsym and R1.4 marginal probability distributions. This could be a hint for nucleons to more exotic particles phase transition inside of the core of neutron stars. We also conclude that increasing the accuracy on the determination of tidal deformability from the gravitational wave, as well as Mc from the isoscalar giant monopole resonance, will lead to a better determination of Ksat and Qsat
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Strachan, N. R. "Magnetic neutral points and nonuniform reconnection." Thesis, University of St Andrews, 1994. http://hdl.handle.net/10023/14250.
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Ever since the first recorded observation of a solar flare in September 1859, it has been a key question - for physics as a whole and for astrophsics in particular - to ask what mechanism lies behind the sudden, violent release of energy from the sun. It has become increasingly apparent that the complex structure of the solar magnetic field lies at the heart of the answer. The process of magnetic reconnection has, over the years, become the accepted explanation by which magnetic energy can be released on both large and small scales in astrophysical and laboratory plasmas. The results of reconnection can be seen, for instance, in star formation, solar flares and the earth's aurorae; indeed the 1859 flare was followed by exceptional auroral activity. The mechanism of magnetic reconnection was first postulated by Giovanelli (1947) as a way of releasing the magnetic energy stored in the Sun. He, and later Dungey (1953), realised that the behaviour of the plasma in the vicinity of a magnetic neutral or null point, where the field disappears, is quite different from other regions of space. In this thesis the nature of magnetic neutral points and their role in the process of reconnection is investigated. Firstly, a general classification of magnetic neutral points is presented. The chapter includes equilibrium and steady-state solutions for two-dimensional magnetic neutral points. The differences in the field behaviour close to each type of neutral point are explained and criteria for the existence of steady-state solutions and equilibria involving pressure balance are presented. In the last section, a self-similar solution for a collapsed X-point is explored. The X-point necessarily becomes cusp-like in nature if shearing is applied in the ignorable direction. Two reconnection models are considered. The first is an extension of the Priest-Lee model (1990). It incorporates large pressure gradients in the inflow corresponding to the Forbes-Priest Almost-Uniform Model. The investigation includes both analytical and numerical solutions and a study of the separatrix jet. In the numerical study, current spikes are found at the end of the current sheets and a much increased reconnection rate is found analytically in the extreme flux file-up limit. The second reconnection model presented is also based on the Priest-Lee configuration. A uniform field is imposed on the basic structure producing a cusp-point with a non-zero field strength as the neutral point is approached from above. This results in the removal of the singularity in the flow above the separatrix. A non-singular solution is found analytically for a double-cusp. A much larger reconnection rate is found and a numerical solution is presented.
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Kramp, Sirko. "Magnetische Anregungen und Achsenkonversion in NdCu2." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2001. http://nbn-resolving.de/urn:nbn:de:swb:14-994770952656-27205.
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Die Arbeit beinhaltet eine Untersuchung der magnetischen Anregungen in NdCu2 mittels inelastischer Neutronenstreuung. Die Zielsetzung besteht darin, die zur Beschreibung der magnetischen Eigenschaften notwendige Austauschwechselwirkung zu charakterisieren. Dazu wurden die Spinwellendispersionsrelationen in mehreren magnetischen Phasen gemessen (ferro-, ferri-, antiferromagnetisch; magnetische Momente parallel b). Die Lage der in der ferromagnetischen Phase F3 erwarteten zwei Dispersionszweige konnte vollständig bestimmt werden. Auffälligstes Merkmal ist ein ausgeprägtes Minimum an der Stelle q=(0.35,0,0), welches eine Energielücke im Anregungsspektrum definiert. Die Lage des Minimums fällt mit keinem der in NdCu2 beobachteten magnetischen Ordnungsvektoren zusammen, wodurch die starke magnetischen Anisotropie des Systems zum Ausdruck kommt. An die experimentell ermittelte Spinwellendispersion in der Phase F3 wurde ein MF-RPA-Modell angepaßt, welches einen Satz magnetischer Kopplungsparameter liefert. Durch Anwendung dieser Kopplungsparameter auf andere Verbindungen der RCu2-Reihe lassen sich Aussagen zum magnetischen Ordnungsprozeß in diesen Verbindungen machen. Werden die magnetischen Momente durch Anlegen eines starken Magnetfeldes in c-Richtung ausgerichtet, so läßt sich die Austauschkopplung innerhalb der ab-Ebene untersuchen. Die magnetischen Anregungen wurden bei µ0Hc=12T und T=2K gemessen. Das Minimum im Anregungsspektrum liegt jetzt bei q=(0.6,0,0) und damit im Bereich der magnetischen Ordnungsvektoren. Ein besonders interessantes Phänomen innerhalb der RCu2-Reihe ist die sogenannte Achsenkonversion. Mittels elastischer Neutronenstreuung konnte erstmals gezeigt werden, daß eine Achsenkonversion auch in RCu2-Verbindungen auftritt, in denen die leichte Magnetisierungsrichtung parallel zur orthorhombischen b-Achse liegt. In NdCu2 deuten starke magnetostriktive Effekte und das Zusammenbrechen eines Bragg-Reflexes bei µ0Hc=12.5T und T=2K auf einen strukturellen Phasenübergang hin. Im abnehmenden äußeren Magnetfeld relaxieren die strukturellen Änderungen bis zum Erreichen des Nullfeldes nicht. Nach der Konversion wurde zwischen µ0Hc=0T und 6T eine neue antiferromagnetische Phase beobachtet. Die Rückkonversion in den Ausgangszustand erfolgt durch Erwärmung der Probe auf T=130K.
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Yu, Hang Ph D. Massachusetts Institute of Technology. "Astrophysical signatures of neutron stars in compact binaries and experimental improvements on gravitational-wave detectors." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123343.
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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 269-281).
Neutron stars (NSs) are astrophysical laboratories that allow us to probe physics at extreme conditions. The first half of this Thesis is devoted to exploring how we can connect theoretical models of NSs to observational signatures whose detections are made possible by state-of-the-art instruments. We start by exploring the dynamics of super-Eddington winds launched in type-I X-ray bursts at the surface of a NS. We show that freshly synthesized heavy elements can be exposed by the wind and will dominate the composition at the photosphere after ~ 1 s. This may create detectable absorption edges in burst spectra and explain the observed transitions from super-expansions to moderate expansions. Gravitational-wave (GW) observatories such as Advanced LIGO (aLIGO) open up a new possibility to probe deep inside the NS by examining the tidal signatures in the GW waveforms.
In this Thesis, we study the tidal excitations of g-modes in a cold, superfluid NS during the inspiral driven by gravitational radiation and their resulting phase shifts in the GW waveform. We consider both the g-modes supported by the muon-to-electron gradient in the outer core and the g-modes supported by the hyperon-to-proton gradient in the inner core. We further show that the former might be detectable by event stacking with the third generation of GW detectors. The second half of this Thesis is devoted to the experimental upgrades to a LIGO interferometers. The focus will be on the angular sensing and control system. We will cover design considerations on the system based on both stability and noise requirements. This is followed by a thorough discussion of the radiation-pressure torques, including both the Sidles-Sigg and the d[Rho]/d[theta] effects.
More importantly, we show that such optical torques can be compensated for with newly developed techniques, which is a critical step for aLIGO to reach high-power operations. Lastly, we discuss the prospects of detecting GW at 5 Hz with ground-based detectors and demonstrate that low-frequency sensitivity is crucial for both increasing the detection range for black-hole binaries and enabling timely localization of binary NS systems.
by Hang Yu.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Physics
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Galais, Sébastien. "Shock wave and neutrino self-interaction effects upon neutrino flavor conversion in the supernovae environment." Paris 7, 2012. http://www.theses.fr/2012PA077090.
Full textAbstract:
Les travaux présentés dans cette thèse portent sur la conversion de saveur des neutrinos de supernovae. Dans un premier travail, nous avons réalisé le premier calcul complet incluant l'onde de choc et l'auto-interaction pour l'estimation du flux du fond diffus de neutrinos de supernovae (DSNB) arrivant sur terre. Ce flux correspond à la combinaison des neutrinos provenant de toutes les supernovae ayant explose dans l'univers visible. En variant l'angle theta_13 de la matrice de mélange U_MNSP, nous avons montré que l'onde de choc a un impact significatif sur le flux du DSNB. Par la même occasion nous avons propose un modèle simplifié prenant en compte les effets de l'onde de choc et qui pourrait être utilisé pour de futurs calculs du DSNB. Les deux autres travaux se sont concentrés sur la première dérivation analytique exacte de la base de matière en présence de l'auto-interaction. Nous avons souligné, pour le cas à deux saveurs, le rôle important tenu par la phase de matière beta tilde et nous avons établi une condition sur les éléments de l' hamiltonien de saveur pour la fin de la phase de synchronisation et le début des oscillations bipolaires. Via cette base de matière, nous avons identifié en utilisant le formalisme des vecteurs polarisations une correspondance entre les phénomènes de « spectral split » et de résonance magnétique. Ceci nous a permis de confirmer des hypothèses telles que l'adiabaticité de la propagation, l'utilisation du champ magnétique moyen et du référentiel tournant qui avaient été postulé a l'aide d'un modèle simplifié. Une étude préliminaire du cas à trois saveurs nous indique la conservation de cette correspondanceThe works presented in this thesis deal with the flavor conversion of the supernova neutrinos. In a first work, we performed the first complete calculation including the shock wave and the self-interaction for the estimate of the diffuse supernova neutrino background (dsnb) flux arriving on earth. This flux corresponds to the combination of the neutrinos coming from all the supernovae that exploded in the visible universe. By varying the angle theta_13 of the mixing matrix u_mnsp, we showed that the shock wave has a significant impact on the dsnb flux. At the same time we proposed a smplified model that accounts for the shock wave effects and that could be used for future calculations of the dsnb. The other two works are focused on the first exact analytical derivation of the matter basis in the presence of the self-interaction. We underlined, for the two flavors case, the important role of the matter phase beta tilde and we established a condition on the elements of the flavor hamiltonian for the end of the synchronization phase and the onset of the bipolar oscillations. Through the matter basis, we identified, by using the polarization vector formalism, a correspondence between the "spectral split" and the magnetic resonance phenomena. This has allowed us to confirm hypothesis such as the adiabaticity of the propagation, the use of the average magnetic field et the corotating frame that were postulated with the help of smplified models. A prelminary study of the three flavors case indicate us the conservation of this correspondence
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Tringali, Maria Concetta. "Analysis methods for gravitational wave from binary neutron star coalescences: investigation on the post-merger phase." Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368411.
Full textAbstract:
The coalescence of binary neutron stars (BNS) is amongst the most promising sources for advanced gravitational wave (GW) detectors. The forthcoming addition of the advanced Virgo interferometer to the LIGO detector network will greatly improve the estimation of GW characteristics and therefore the capabilities to test features in the GW signal emitted by the coalescence of a NS binary. Such an observation can constrain the equation
of state of these stars in at least two ways: by investigating smaller effects on top of the signal from the inspiral phase due to the tidal deformability of the components and by characterizing the emission from the possible highly excited NS remnant after the merger. Both methods promise to probe matter up to yet unknown and unexplored supranuclear densities, provided that the signal-to-noise ratio (SNR) at which the single GW is detected is sufficiently high or that the results from more detections can be combined together. Depending on mass and Equation of State (EoS) of the NS progenitors,
the final fate of the merger can produce either a prompt collapse to black hole (BH) or a massive NS remnant. In the latter case, the merger remnant could be a short-lived, hypermassive NS (HMNS) collapsing to a BH within a few tens of ms after merger, or a long-lived NS, which in turn can be either supramassive (SMNS), i.e. collapsing to a BH on much longer timescales of order of seconds, or even a stable NS. These remnants will be highly excited, showing transient nonaxisymmetric deformations and quadrupolar oscillations, which are expected to emit GWs peaked in the frequency range around 2-3 kHz. The observation of these Post Merger (PM) fingerprints, would allow to constrain the EoS and at the same time to estimate combinations of stellar parameters, such as
mass and radius of the two objects.
With these motivations, my PhD thesis addressed the development of a new data analysis tool in order to investigate the GW signal emitted during the PM phase following a NS coalescence. The analysis procedure is developed inside the framework of the Coherent Wave Burst (cWB) pipeline which is employed by LIGO and Virgo collaboration to search for burst signals, i.e. it makes minimal assumption on the GW morphology and provides a robust coverage of generic GW transients.
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Tringali, Maria Concetta. "Analysis methods for gravitational wave from binary neutron star coalescences: investigation on the post-merger phase." Doctoral thesis, University of Trento, 2017. http://eprints-phd.biblio.unitn.it/2723/1/TRINGALI_Tesi.pdf.
Full textAbstract:
The coalescence of binary neutron stars (BNS) is amongst the most promising sources for advanced gravitational wave (GW) detectors. The forthcoming addition of the advanced Virgo interferometer to the LIGO detector network will greatly improve the estimation of GW characteristics and therefore the capabilities to test features in the GW signal emitted by the coalescence of a NS binary. Such an observation can constrain the equation
of state of these stars in at least two ways: by investigating smaller effects on top of the signal from the inspiral phase due to the tidal deformability of the components and by characterizing the emission from the possible highly excited NS remnant after the merger. Both methods promise to probe matter up to yet unknown and unexplored supranuclear densities, provided that the signal-to-noise ratio (SNR) at which the single GW is detected is sufficiently high or that the results from more detections can be combined together. Depending on mass and Equation of State (EoS) of the NS progenitors,
the final fate of the merger can produce either a prompt collapse to black hole (BH) or a massive NS remnant. In the latter case, the merger remnant could be a short-lived, hypermassive NS (HMNS) collapsing to a BH within a few tens of ms after merger, or a long-lived NS, which in turn can be either supramassive (SMNS), i.e. collapsing to a BH on much longer timescales of order of seconds, or even a stable NS. These remnants will be highly excited, showing transient nonaxisymmetric deformations and quadrupolar oscillations, which are expected to emit GWs peaked in the frequency range around 2-3 kHz. The observation of these Post Merger (PM) fingerprints, would allow to constrain the EoS and at the same time to estimate combinations of stellar parameters, such as
mass and radius of the two objects.
With these motivations, my PhD thesis addressed the development of a new data analysis tool in order to investigate the GW signal emitted during the PM phase following a NS coalescence. The analysis procedure is developed inside the framework of the Coherent Wave Burst (cWB) pipeline which is employed by LIGO and Virgo collaboration to search for burst signals, i.e. it makes minimal assumption on the GW morphology and provides a robust coverage of generic GW transients.