Dissertations / Theses on the topic 'Gravitational waves'
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Takahashi, Ryuichi. "Wave Effects in the Gravitational Lensing of Gravitational Waves from Chirping Binaries." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147805.
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Herrera, Martín Antonio. "Wave dark matter as a gravitational lens for electromagnetic and gravitational waves." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/9027/.
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The majority of the matter in the known universe is believed to be in the form of Dark Matter, and its widely accepted description is done by Cold Dark Matter (CDM). Nevertheless, its exact properties and composition are still unknown, and it is one of the most active areas of research in Cosmology. The use of Cold Dark Matter has been successful to describe the general behaviour of Dark Matter at large scales. However, it has encountered problems explaining phenomena at other regimes as on the scale of galaxy halos. Therefore, other models have been proposed over time which are able to retain the reasonable success of CDM on large scales and extent it to other regimes where CDM has problems to explain the observed data. One of such models is Scalar field Dark Matter (SFDM). Its properties allow it to produce similar results at large scales and solve the problems encountered at galactic scales. Nevertheless, the difficulty to obtain direct observations of Dark Matter makes it difficult to give a definitive comparison between the models. Therefore, it is important to study dark matter through different methods of analysis that would allow to increase the validity of its scope, and these methods are constantly being researched. In this work, a particular density profile known as Wave Dark Matter is implemented as a gravitational lens to study its behaviour in the cases where it produces strong lensing of light and of gravitational waves. Analytical functions for the description of a soliton core and a soliton core + NFW tail are applied to a sub-sample of 6 galaxies from The Sloan Lens ACS Survey to constrain the lensing parameters and their relation with the profile. Furthermore, by considering the soliton core to be the main contributor to the mass profile, this is implemented as a lens for the case of the wave approximation and further to describe the major effects of the lens on gravitational waves. It was found that the soliton core is too compact and dense in order to reproduce the observed values of the data for the lensed galaxies. However, adding a NFW tail alleviates the problem and reaches radii and masses within the range reported in the literature, although the size of the NFW tail cannot be properly constrained. Meanwhile for gravitational waves, it was found that the lensing parameters of the soliton core, if they are expected to describe a galaxy, will be such that they are more likely to be observed spaceborne gravitational wave detectors. In summary, therefore, a wave dark matter soliton in combination with a NFW tail is able to represent a galaxy, and the combination of ligh and gravitational waves should give new insight on the validity of the profile as a description of Dark Matter galactic haloes.
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Onuk, Ahmet Emre. "Collision Of Gravitational Waves: Axisymmetric Pp Waves." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608696/index.pdf.
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The collision of impulsive gravitational waves, electromagnetic plane waves with collinear polarization and, especially, plane fronted parallel waves (pp waves) are considered. The solution of axisymmetric pp waves is reviewed and the structures of the resulting space-times are investigated with the help of curvature invariants.
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Moore, Christopher James. "Gravitational waves : understanding black holes." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/257043.
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This thesis concerns the use of observations of gravitational waves as tools for astronomy and fundamental physics. Gravitational waves are small ripples in spacetime produced by rapidly accelerating masses; their existence has been predicted for almost 100 years, but the first direct evidence of their existence came only very recently with the announcement in February 2016 of the detection by the LIGO and VIRGO collaborations. Part I of this thesis presents an introduction to gravitational wave astronomy, including a detailed discussion of a wide range of gravitational wave sources, their signal morphologies, and the experimental detectors used to observe them. Part II of this thesis concerns a particular data analysis problem which often arises when trying to infer the source properties from a gravitational wave observation. The use of an inaccurate signal model can cause significant systematic errors in the inferred source parameters. The work in this section concerns a proposed technique, called the Gaussian process marginalised likelihood, for overcoming this problem. Part III of this thesis concerns the possibility of testing if the gravitational field around an astrophysical black hole conforms to the predictions of general relativity and the cosmic censorship hypothesis. It is expected that the gravitational field should be well described by the famous Kerr solution. Two approaches for testing this hypothesis are considered; one using X-ray observations and one using gravitational waves. The results from these two approaches are compared and contrasted. Finally, the conclusions and a discussion of future prospects are presented in part IV of this thesis.
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Siemens, Xavier. "Gravitational waves and cosmic strings /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2002.
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Thesis (Ph.D.)--Tufts University, 2002.Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 95-98). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Bello, Arufe Aaron. "Gravitational Waves in General Relativity." Thesis, Umeå universitet, Institutionen för fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-136721.
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In this paper, we write a summary about general relativity and, in particular,gravitational waves. We start by discussing the mathematics that generalrelativity uses, as well as the geometry in general relativity's spacetime. Afterwards,we explain linearized general relativity and derive the linearizedversions of Einstein's equations. From here, we construct wave solutionsand explain the polarization of gravitational waves. The quadrupole formulais derived, and generation and detection of gravitational waves is brie ydiscussed. Finally, LIGO and its latest discovery of gravitational waves isreviewed.
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Lagger, Cyril Oscar. "Gravitational Waves and Fundamental Physics." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20810.
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This thesis investigates the implications of gravitational waves (GWs) for particle physics and cosmology. We first give an overview of the current state of general relativity and quantum field theory. We also emphasize where GWs may come into play to shed new light on unsolved problems in physics. First, we make use of GWs to constrain the scale of non-commutative space-time. Assuming such quantum fuzziness, we compute the equations of motion of a binary black hole and the associated generation of GWs. Compared to general relativity, leading non-commutative effects produce a post-Newtonian correction of order (v/c)^4. Using the recent GW150914 signal, we find that the scale of non-commutativity is bounded to be below or at the order of the Planck scale. This represents an improvement of ~15 orders of magnitude compared to previous constraints. Second, we study the production of GWs from cosmological phase transitions. We consider two unrelated extensions of the standard model: a non-linear realization of the electroweak gauge group and a model with hidden scale invariance. In the first case, the Higgs vacuum configuration is altered by a cubic coupling giving the possibility to have a strong and prolonged electroweak first-order transition. In our second model, the electroweak transition cannot proceed until it is triggered by a first-order QCD chiral symmetry breaking around 130 MeV. We compute that the stochastic GW background produced during these two phase transitions is expected to be in the detection range of pulsar timing arrays. Finally, we investigate the backreaction of particle production on false vacuum decay. We present a formalism which makes use of the reduced density matrix of the system to quantify the impact of these particles on the decay rate of a scalar field in flat space-time. We then apply this method to a toy model potential and we exhibit different scenarios with either significant or negligible backreaction.
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Corbin, Vincent Dominique Andre. "Studying cosmological sources of gravitational waves." Diss., Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/corbin/CorbinV1210.pdf.
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This dissertation presents two aspects of the study of cosmology through gravitational waves. The first aspect involves direct observation of past eras of the Universe's formation. The detection of the Cosmic Microwave Background Radiation was one of the most important cosmological discoveries of the last century. With the development of interferometric gravitational wave detectors, we may be in a position to detect its gravitational equivalent in this century. The Cosmic Gravitational Background is likely to be isotropic and stochastic, making it difficult to distinguish from instrument noise. The contribution from the gravitational background can be isolated by cross-correlating the signals from two or more independent detectors. Here we extend previous studies that considered the cross-correlation of two Michelson channels by calculating the optimal signal to noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer. We apply our results to the detector design described in the Big Bang Observer mission concept study and find that it could detect a background with Omega gw > 2.2 x 10 ̄¹â·. The second aspect consists in studying astrophysical sources that detain crucial information on the Universe's evolution. We focus our attention on black holes binary sytems. These systems contain information on the rate of merger between galaxies, which in turn is key to unlock the mystery of inflation. Pulsar timing is a promising technique for detecting low frequency sources of gravitational waves, such as massive and supermassive black hole binaries. Here we show that the timing data from an array of pulsars can be used to recover the physical parameters describing an individual black hole binary to good accuracy, even for moderately strong signals. A novel aspect of our analysis is that we include the distance to each pulsar as a search parameter, which allows us to utilize the full gravitational wave signal. This doubles the signal power, improves the sky location determination by an order of magnitude, and allows us to extract the mass and the distance to the black hole binary.
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Gholami, Ghadikolaei Iraj. "Data analysis of continuous gravitational waves." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1880/.
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This thesis describes two main projects; the first one is the optimization of a hierarchical search strategy to search for unknown pulsars. This project is divided into two parts; the first part (and the main part) is the semi-coherent hierarchical optimization strategy. The second part is a coherent hierarchical optimization strategy which can be used in a project like Einstein@Home. In both strategies we have found that the 3-stages search is the optimum strategy to search for unknown pulsars.
For the second project we have developed a computer software for a coherent Multi-IFO (Interferometer Observatory) search. To validate our software, we have worked on simulated data as well as hardware injected signals of pulsars in the fourth LIGO science run (S4). While with the current sensitivity of our detectors we do not expect to detect any true Gravitational Wave signals in our data, we can still set upper limits on the strength of the gravitational waves signals. These upper limits, in fact, tell us how weak a signal strength we would detect. We have also used our software to set upper limits on the signal strength of known isolated pulsars using LIGO fifth science run (S5) data.Diese Dissertation besteht aus zwei Projekten: Im ersten Projekt wird die Optimierung einer hierarchischen Strategie zum Auffinden von 'unbekannten' Pulsaren beschrieben. Der erste Teil besteht dabei aus einer semi-kohärenten und der zweite Teil aus einer kohärenten Optimierungsstrategie, wie sie in Projekten wie Einstein@Home verwendet werden kann. In beiden Ansätzen erwies sich eine 3-Stufensuche als optimale Suchstrategie für 'unbekannte' Pulsare. Für das zweite Projekt entwickelten wir eine Software für eine kohärente Multi-IFO (Interferometer Observatory) Suche. Zum Validieren der Software verwendeten wir sowohl simulierte Daten als auch Hardware induzierte Signale von Pulsaren aus dem vierten 'LIGO Science run' (S4). Wir erwarten nicht, mit der aktuellen Empfindlichkeit unserer Detektoren echte GW- Signale aufzunehmen, können jedoch obere Grenzen für die Stärke der Gravitationswellen-Signale bestimmen. Diese oberen Grenzen geben uns an, wie schwach ein gerade noch detektierbares Signal werden kann. Ferner benutzten wir die Software um eine obere Grenze für bekannte, isolierte Pulsare zu bestimmen, wobei wir Daten aus dem fünften 'LIGO Science run (S5) verwendeten.
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Williamson, Andrew Robert. "Gravitational waves with gamma-ray bursts." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/96479/.
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Gravitational waves have now twice been detected emanating from the merging of binary black hole systems. In this thesis we detail the methods used to search for binary merger gravitational wave signals associated with short gamma-ray bursts, focusing on systems that include at least one neutron star. We first cover the background theory behind gravitational wave emission, the means of detection via interferometry, and the types of astrophysical sources that could be detected now or in the near future. We follow this with a review of gamma-ray burst theory and observations, focusing in particular those bursts with short durations. These are likely to be caused by the mergers of binaries that include a neutron star and a black hole, or two neutron stars - events of great interest to gravitational wave astronomy. We then discuss the methods used to search gravitational wave data in a targeted way, using the prior observation of a short gamma-ray bursts to focus the analysis and improve the chances of making a detection. We also summarise early searches of this kind and present the results of a search carried out on LIGO and Virgo data spanning 2005-2010, targeting short gamma-ray bursts detected by the InterPlanetary Network. We then turn our attention to the current, second generation of gravitational wave detectors. We present a detailed calculation of the prospects of success for the targeted short gamma-ray burst search technique, and find that we might reasonably expect to make up to a few detections per year around the turn of the decade. We then outline a new search structure for use during the second generation of detectors, and an astrophysical event alert system for the control rooms of gravitational wave observatories. We end with a presentation of the results of the new and improved search carried out during the first observing run of Advanced LIGO.
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Key, Joey Shapiro. "Characterizing astrophysical sources of gravitational waves." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/key/KeyJ0510.pdf.
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The Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational-wave Observatory (LIGO) are designed to detect gravitational waves from a wide range of astrophysical sources. The parameter estimation ability of these detectors can be determined by simulating the response to predicted gravitational wave sources with instrument noise and searching for the signals with sophisticated data analysis methods. A possible source of gravitational waves will be beams of radiation from discontinuities on cosmic length strings. Cosmic strings are predicted to form kinks and cusps that travel along the string at close to the speed of light. These disturbances are radiated away as highly beamed gravitational waves that produce a burst-like pulse as the cone of emission sweeps past an observer. The detection of a gravitational wave signal from a cosmic string cusp would illuminate the fields of string theory, cosmology, and relativity. Gravitational wave sources also include coalescing binary systems of compact objects. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Previous LISA data analysis studies have assumed that binary black hole systems have a circular orbit or an extreme mass ratio. It is ultimately necessary to understand the general case of spinning black hole binary systems in eccentric orbits and how LISA observations can be used to measure the eccentricity of the orbits as well as the masses, spins, and luminosity distances of the black holes. Once LISA is operational, the comparison of observations of eccentric and circular black hole binary sources will constrain theories on galaxy mergers in the early universe.
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Christie, David C. "Gravitational tidal effects on electromagnetic waves." Thesis, Lancaster University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431471.
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Maia, Marcio Roberto de Garcia. "The stochastic background of gravitational waves." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384851.
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Taylor, Stephen Richard. "Exploring the cosmos with gravitational waves." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708426.
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Ramirez, David Alejandro Tamayo. "Gravitational Waves in Decaying Vacuum Cosmologies." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06012016-144604/.
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In the present monograph we study in detail the primordial gravitational waves in cosmologies with a decaying vacuum. The decaying vacuum models are an alternative to solve the cosmological constant problem attributing a dynamic to the vacuum energy. The problem of primordial gravitational waves is discussed in the framework of an expanding, flat, spatially homogeneous and isotropic FLRW Universe described by General Relativity theory with decaying vacuum energy density of the type $\\Lambda \\equiv \\Lambda(H)$. Two particular interesting limits of a class of decaying vacuum models were investigated. A first-order tensor perturbation term was introduced to the FLRW metric, the evolution equation of the perturbations was derived and then expressed in terms of a Fourier expansion, the time-dependent part decouples from the spatial part. The resulting equation has the form of a damped harmonic oscillator which depends on the scale factor, which carries all the cosmological and decaying vacuum characteristics. In the first model studied, the decaying vacuum has the form $\\Lambda \\propto H^2$. The gravitational wave equation is established and its time-dependent part has analytically been solved for different epochs in the case of a flat geometry. The main result is unlike the standard $\\Lambda$CDM cosmology (no interacting vacuum): in this model there is gravitational wave amplification during the radiation era, which in quantum field theory means graviton production. This difference is a clear signature of the decaying vacuum models which a eventual observation could give empirical clues about it. However, high frequency modes are damped out even faster than in the standard cosmology, both in the radiation and matter-vacuum dominated epoch. The physical gravitational wave quantities like the modulus of the mode function, power and gravitational wave energy density spectra generated at different cosmological eras are also explicitly evaluated. The second model studied is a decaying vacuum of the form $\\Lambda \\propto H^3$. This model drives a nonsingular flat cosmology which is termed complete in the sense that the cosmic evolution occurs between two extreme de Sitter stages. The particularity which makes interesting this model is that the transition from the early de Sitter era to the radiation phase is smooth avoiding the graceful exit problem. The gravitational wave equation is derived and its time-dependent part numerically integrated in a relevant period previously delimited. The gravitational wave solutions for the other eras were calculates analytically. Today\'s gravitational wave spectra were calculated and compared with the standard result where an abrupt transition is assumed. It is found that the stochastic background of gravitational waves is very similar to the one predicted by the cosmic concordance model plus inflation except for the higher frequencies.Na presente monografia foi estudado em detalhe as ondas gravitacionais primordiais em cosmologias com decaimento do vácuo. Os modelos de decaimento do vácuo são uma alternativa para resolver o problema da constante cosmológica atribuindo uma dinâmica à energia do vácuo. O problema de ondas gravitacionais primordiais é discutida no âmbito de um Universo FLRW em expansão, plano, espacialmente homogêneo e isotrópico descrito pela teoria da Relatividade Geral com decaimento da densidade de energia do vácuo do tipo $\\Lambda \\equiv \\Lambda(H)$. Dois limites particularmente interessantes de uma classe de modelos de decaimento do vácuo foram trabalhados. Um termo tensorial perturbativo a primeira ordem foi introduzido na métrica de FLRW, a equação de evolução das perturbações foi derivada e depois expressada em termos de uma expansão de Fourier, a parte dependente do tempo desacopla-se da parte espacial. A equação resultante tem a forma de um oscilador harmônico amortecido que depende do fator de escala que carrega todas as características cosmológicos e do decaimento do vácuo. No primeiro modelo estudado, o decaimento do vácuo tem a forma $\\Lambda \\propto H^2$. A equação da onda gravitacional é estabelecida e a sua parte dependente do tempo foi resolvida analiticamente para diferentes épocas no caso de uma geometria plana. O resultado principal é que a diferença da cosmologia $\\Lambda$CDM padrão (sem decaimento do vácuo), neste modelo ocorre amplificação de ondas gravitacionais durante a era de radiação, que em mecânica quântica significa produção gráviton. Esta diferença é uma assinatura clara dos modelos de decaimento do vácuo que uma eventual observação poderia dar pistas empíricas sobre o assunto. No entanto, os modos de alta frequência são amortecidos ainda mais rápido do que na cosmologia padrão, tanto na era da radiação e da matéria-vácuo. As quantidades físicas das ondas gravitacionais, como o módulo da função de modos, espectros de potência e de densidade de energia de onda gravitacional geradas em diferentes eras cosmológicas também foram avaliadas explicitamente. O segundo modelo estudado é um decaimento do vácuo da forma $\\Lambda \\propto H^3$. Este modelo leva uma cosmologia plana não singular que é denominado completo no sentido de que a evolução cósmica ocorre entre duas eras de Sitter extremas. A particularidade que torna interessante este modelo é que a transição do início da era de Sitter era para a fase da radiação é suave evitando o graceful exit problem. A equação gravitacional é derivada e sua parte dependente do tempo foi integrada numericamente num período relevante previamente delimitado, as soluções das ondas gravitacionais para as outras eras foram calculadas analiticamente. Os espectros de hoje das ondas gravitacionais foram calculados e comparados com os cálculos padrão onde é assumida uma transição abrupta. Verificou-se que o fundo estocástico de ondas gravitacionais é muito semelhante ao previsto pelo modelo de concordância cósmica mais a inflação, exceto para as frequências mais altas.
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Gill, Colin D. "Searching for gravitational waves from pulsars." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3754/.
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The work presented here looks at several aspects of searching for continuous gravitational waves from pulsars, often referred to simply as continuous waves or CWs. This begins with an examination of noise in the current generation of laser interferometer gravitational wave detectors in the region below ~100 Hz. This frequency region is of particular interest with regards to CW detection as two prime sources for a first CW detection, the Crab and Vela pulsars, are expected to emit CWs in this frequency range. The Crab pulsar's frequency lies very close to a strong noise line due to the 60 Hz mains electricity in the LIGO detectors. The types of noise generally present in this region are discussed. Also presented are investigations into the noise features present in the LIGO S6 data and the Virgo VSR2 data using a program called Fscan. A particular noise feature present during VSR2 was discovered with the use of Fscan, which I report on and show how it degrades the sensitivity of searches for CWs from the Vela pulsar using this data. I next present search results for CWs from the Vela pulsar using VSR2 and VSR4 data. Whilst these searches did not find any evidence for gravitational waves being present in the data, they were able to place upper limits on the strength of gravitational wave emission from Vela lower than the upper limit set by the pulsars spin-down, making it only the second pulsar for which this milestone has been achieved. The lowest upper limit derived from these searches confines the spin-down energy lost from Vela due to gravitational waves as just 9% of Vela's total spin-down energy. The data from VSR2 and VSR4 are also examined, analysis of hardware injections in these datasets verify the calibration of the data and the search method. Similar results are also presented for a search for CWs from the Crab pulsar, where data from VSR2, VSR3, VSR4, S5 and S6 are combined to produce an upper limit on the gravitational wave (GW) amplitude lower than has been previously possible, representing 0.5% of the energy lost by the pulsar as seen through its spin-down. The same search method is also applied to analyse data for another 110 known pulsars, with five of these being gamma-ray pulsars that have been timed by the Fermi satellite. GWs from the pulsars timed by Fermi are expected at frequencies below 40 Hz, the LIGO detectors are not calibrated below these frequencies but the Virgo detector is. Hence the data used to search for GWs from these pulsars is the Virgo VSR4 data. The other 105 pulsars were analysed using out of date ephemerides obtained for the LIGO S5 run and the data analysed was from the LIGO S6 run, hence the results obtained for these pulsars are presented as an indication of what results can be expected with updated ephemerides only. For these 110 pulsars the spin-down limits were not able to be beaten, although there are a few pulsars for which this may be able to be achieved with an analysis combining all the possible datasets, in particular J1913+1011. The final part of this thesis reports extensions to the search method used for the analyses previously described. The first way in which this search method is extended is the use of a nested sampling algorithm to perform the parameter estimation stage of the analysis which was previously preformed using a MCMC. The nested sampling code also allows for model selection through the computation of the Bayesian evidence, I present results from characterisation tests of this nested sampling search code that demonstrate the equivalence of its results to those from the MCMC and grid based codes. The other extension to the search method looks at a new CW emission mechanism from a neutron star with a pinned superfluid core that is misaligned from the star's principle axes. This emission model predicts CWs at both the stars spin frequency f and twice its spin frequency 2f, providing an extra data channel with which to perform a search when compared to the triaxial rotator model which only emits at 2f. I present the development of a search for the emission from this new model, tests of the algorithm developed using simulated data, and results from a search using actual data from the VSR4 run for CWs from the Crab pulsar. The testing of the search algorithm shows that the posterior for the model is sufficiently complex to inhibit useful parameter estimation, but that the computation of the Bayesian evidence allows one to distinguish between this model and the triaxial rotator given a low SNR signal in the f data channel.
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Ekehult, Joanna, and Anna Karpinska. "Gravitational Waves and Coalescing Black Holes." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210848.
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Gravitation is a manifestation of the space-time curvature and gravitational waves aredistortions traveling through the fabric of space-time. Scientists have tried to detectgravitational waves for decades, but the first direct detection of gravitational waves andthe first observation of a binary black hole merger was made in 2015. The purpose ofthis report is to introduce General Relativity and binary black holes and to calculate thetime to coalescence of two back holes with circular or elliptical orbits. We find that abinary black hole in an elliptical orbit with large eccentricity coalesces faster than in acircular orbit.
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Joanna, Ekehult, and Anna Karpinska. "Gravitational Waves and Coalescing Black Holes." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210849.
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Gravitation is a manifestation of the space-time curvature and gravitational waves aredistortions traveling through the fabric of space-time. Scientists have tried to detectgravitational waves for decades, but the first direct detection of gravitational waves andthe first observation of a binary black hole merger was made in 2015. The purpose ofthis report is to introduce General Relativity and binary black holes and to calculate thetime to coalescence of two back holes with circular or elliptical orbits. We find that abinary black hole in an elliptical orbit with large eccentricity coalesces faster than in acircular orbit.
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Seader, Shawn Eugene 1978. "Multi-interferometer search methods for gravitational waves." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/s%5Fseader%5F120705.pdf.
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Forsberg, Mats. "Gravitational perturbations in plasmas and cosmology." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-38387.
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Gravitational perturbations can be in the form of scalars, vectors or tensors. This thesis focuses on the evolution of scalar perturbations in cosmology, and interactions between tensor perturbations, in the form of gravitational waves, and plasma waves. The gravitational waves studied in this thesis are assumed to have small amplitudes and wavelengths much shorter than the background length scale, allowing for the assumption of a flat background metric. Interactions between gravitational waves and plasmas are described by the Einstein-Maxwell-Vlasov, or the Einstein-Maxwell-fluid equations, depending on the level of detail required. Using such models, linear wave excitation of various waves by gravitational waves in astrophysical plasmas are studied, with a focus on resonance effects. Furthermore, the influence of strong magnetic field quantum electrodynamics, leading to detuning of the gravitational wave-electromagnetic wave resonances, is considered. Various nonlinear phenomena, including parametric excitation and wave steepening are also studied in different astrophysical settings. In cosmology the evolution of gravitational perturbations are of interest in processes such as structure formation and generation of large scale magnetic fields. Here, the growth of density perturbations in Kantowski-Sachs cosmologies with positive cosmological constant is studied.
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Izquierdo, Sáez Germán. "Relic gravitational waves in the expanding Universe." Doctoral thesis, Universitat Autònoma de Barcelona, 2005. http://hdl.handle.net/10803/3372.
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Las ondas gravitatorias primordiales representan una ventana privilegiada para determinar la evolución del Universo, ya que a partir de su espectro seria posible reconstruir el factor de escala desde los instantes iniciales de expansión hasta el instante presente. En esta tesis, trabajando en aproximación de vacío adiabático, hemos revisado como la expansión del Universo amplifica las fluctuaciones del vacío cuántico. Hemos evaluado el espectro en un modelo de expansión del universo que considera una era inicial inflacionaria, una era dominada por agujeros negros primordiales y radiación, una era dominada por radiación y finalmente una era de la materia. Hemos demostrado como el espectro de este escenario es mucho menor que el del modelo habitual (inflación- era de radiación-era de materia), también hemos visto como las anisotropías observadas del CMB ponen limites a los parámetros libres del modelo de las cuatro eras. Hemos calculado el espectro en un modelo con un universo dominado por energía oscura en la era presente, concluyendo que pese a que este espectro coincide con el del escenario de las tres eras evoluciona de manera diferente. También hemos calculado el espectro en una hipotética segunda era de la materia, en el caso de que esta era de expansión acelerada sea sólo una etapa transitoria. Hemos estudiado como se cumple la segunda ley de la termodinámica durante la era de expansión acelerada, asignando una entropía a las ondas gravitatorias primordiales que debe cumplir una determinada condición. Finalmente, dejando de lado las ondas gravitatorias, hemos estudiado la segunda ley de la termodinámica en universos dominados por energía oscura fantasma, concluyendo que la entropía de estos fluidos es negativa y que la segunda ley es respetada.Cosmology has for a long time been a rather speculative science. Hubble's discovery that the Universe is expanding, and -more recently- the realization that at present this expansion is accelerated, the measured abundance of light elements, the mass distribution of galaxies and clusters thereof, and the discovery and posterior measurements of the anisotropies of the CMB have changed this picture. Hopefully, measurements of GWs will soon be added to this short list. At any rate, now we can speak confidently of physical cosmology as a fully-fledged branch of Science. The relic GWs constitute a privileged window to determine the evolution of the Universe. Little is known from the early evolution of the Universe and the predictions for their spectrum depend on the model considered. According to these predictions, a spectrum of relic GWs is generated making feasible its detection with the technology currently being developed. In this thesis, using the adiabatic vacuum approximation, we have reviewed how the expansion of the Universe amplifies the quantum vacuum fluctuations, and how the relic GWs spectrum is related with the scale factor. We have later evaluated the spectrum in a four-stage model (which consist on a De Sitter stage, a stage dominated by a mixture of MBHs and radiation, a radiation dominated stage and finally a non-relativistic matter (dust) dominated stage). We have demonstrated that the spectrum in this scenario is much lower than the predicted by three-stage model (De Sitter-radiation era-dust era). We have also shown how the bound over the GWs spectrum from the measured CMB anisotropies places severe constraints over the free parameters of the four-stage model. We have also considered a scenario featuring an accelerated expanding era dominated by dark energy, right after the dust era of the three-stage model. We have found that the current power spectrum of this four-stage scenario exactly coincides with that of the three-stage, but it evolves in a different fashion. We have considered as well the possibility that the dark energy decays in non-relativistic matter leading to a second dust era in the far future and obtained the power spectrum of the GWs as well as the evolution of the density parameter. We have applied the generalized second law of thermodynamics to the four-stage model of above. Assuming the GWs entropy proportional to the number of GWs, we have found the GSL is fulfilled provided a certain proportionality constant does not exceed a given upper bound. Finally, we have extended the GSL study to a single stage universe model dominated by dark energy (either phantom or not), and found that the GSL is satisfied and that the entropy of the phantom fluid is negative. Likewise, we have found a transformation between phantom and non-phantom scenarios preserving the Einstein field equations that entails a "quasi" duality between the thermodynamics of both scenarios.
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Cambaz, Efsun. "Colliding Gravitational Plane Waves: Bell-szekeres Solution." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606342/index.pdf.
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The collision of pure electromagnetic plane waves with collinear polarization in Einstein-Maxwell theory and the collision of gravitational plane waves in vacuum Einstein theory are studied. The singularity structure of the Bell-Szekeres and the Szekeres solutions is examined by using curvature invariants. As a final work, the collision of the plane waves in dilaton gravity theory is studied and also the singularity structure of the corresponding space-time is examined.
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Predoi, Valeriu. "Gravitational waves and short gamma ray bursts." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/39987/.
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Short hard gamma-ray bursts (GRB) are believed to be produced by compact binary coalescences (CBC) { either double neutron stars or neutron star{black hole binaries. The same source is expected to emit strong gravitational radiation, detectable with existing and planned gravitational wave observatories. The focus of this work is to describe a series of searches for gravitational waves (GW) from compact binary coalescence (CBC) events triggered by short gamma-ray burst detections. Specifically, we will present the motivation, frameworks, implementations and results of searches for GW associated with short gamma-ray bursts detected by Swift, Fermi{GBM and the InterPlanetary Network (IPN) gamma-ray detectors. We will begin by presenting the main concepts that lay the foundation of gravitational waves emission, as they are formulated in the theory of General Relativity; we will also brie y describe the operational principles of GW detectors, together with explaining the main challenges that the GW detection process is faced with. Further, we will motivate the use of observations in the electromagnetic (EM) band as triggers for GW searches, with an emphasis on possible EM signals from CBC events. We will briefly present the data analysis techniques including concepts as matched{filtering through a collection of theoretical GW waveforms, signal{to{ noise ratio, coincident and coherent analysis approaches, signal{based veto tests and detection candidates' ranking. We will use two different GW{GRB search examples to illustrate the use of the existing coincident and coherent analysis methods. We will also present a series of techniques meant to improve the sensitivity of existing GW triggered searches. These include shifting background data in time in order to obtain extended coincident data and setting a prior on the GRB inclination angle, in accordance with astrophysical observations, in order to restrict the searched parameter space. We will describe the GW data analysis and present results from a GW search around 12 short gamma-ray bursts detected by the InterPlanetary Network (IPN) between 2006 and 2007. The IPN{detected bursts usually have extended localization error boxes and a search for GW was performed at different sky locations across these error regions. Since no GW detection was made, we set upper limits on the distances to the GRB progenitors; we briefly discuss the implications that two IPN GRBs error regions overlap two nearby galaxies.
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Schluessel, Edmund Rudolph. "Long-wavelength gravitational waves and cosmic acceleration." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/38028/.
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Multiple observations of distant type Ia supernovae show the deceleration parameter of the universe is negative. The standard cosmological model states expansion should be slowing down. A new theory is presented which explains cosmic acceleration only through the action of well-supported phenomena in the context of Einstein's general theory of relativity through the use of the Bianchi type IX homogeneous,closed cosmology. The evidence for acceleration is assessed and previously-unreported biases and insuffiencies in the evidence are revealed and discussed. The Einstein equations for the Bianchi type IX cosmology are solved to quadratic order in a matter-dominated universe. The first terms of a power-series solution are given for arbitrarily strong growing mode of gravitational waves in a matter-dominated Bianchi IX universe. The effect of these waves on the energy density of the universe is shown to becompatible with available data. The equations for redshift anisotropy in the Bianchi IX universe are solved to quadratic order. Reported anomalous structure in the cosmic microwave back-ground is considered in the light of these solutions. The Bianchi IX universe is shown to provide an explanation for these anomalies compatible with the CMB. In order to help typify a new class of standard sour es for determining cosmological parameters, a formula relating the time-dependent detection of light by a massive, compact binary such as a super-massive black hole binary is derived. This formula is applied to the system 3C66B and finds that in ideal circumstances, the best available observational techniques would detect a time-dependent omponent to the bending of light by the core of 3C66B. A solution for the Einstein equations in the Bianchi IX universe is found which explains cosmic acceleration while remaining compatible with the CMB and other cosmological parameters as reported by WMAP.
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Dupuis, Réjean J. "Bayesian searches for gravitational waves from pulsars." Thesis, University of Glasgow, 2004. http://theses.gla.ac.uk/5714/.
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Methods for searching for periodic gravitational wave signals from triaxial pulsars using interferometric gravitational wave detectors have been developed. Since the gravitational wave signals from pulsars are expected to be weak, long stretches of data must be used for any detection. Over the course of a day, and a year, these periodic signals are Doppler shifted due to the motion of the Earth. The response of the interferometers to each polarisation of gravitational waves will also give rise to an amplitude modulation of the periodic signal. These effects are taken into account and an end-to-end Bayesian scheme for making inferences from the data is presented. Several software tests have been performed to validate the core routines, such as barycentring, using independent software. The GEO 600 and LIGO interferometers had their first scientific data run (S1) for 17 days between 23 August and 9 September 2002. An analysis was carried out to search for gravitational wave signals from pulsar B1937+21. While no signals were detected, a 95% upper limit of h0 < 1.4 x 10-22 was determined using S1 data where h0 is the amplitude of the gravitational waves. Given that pulsar B1937+21 is at a distance of 3.6 kpc, and assuming a moment of inertia of 1038kg m2, the corresponding upper limit on the equatorial ellipticity was determined to be = 2.9 x 10-4. The upper limit on gravitational waves from pulsar B1937+21 using S1 data was over an order of magnitude lower than the previous best limit at the time. Data from LIGO's second science run (S2) in the spring of 2003 was analysed with the sensitivity of each detector in the network being roughly an order of magnitude better than in S1 across a large range of frequencies. Upper limits were placed on a total of 28 isolated pulsars using the S2 data. The analysis procedure for S2 was more robust to interfering spectral lines and took advantage of the longer stationarity of the S2 data. Two hardware injections of hypothetical pulsars were injected in the LIGO interferometers during S2. The successful extraction of these signals from the LIGO S2 data significantly increased our confidence in the the overall data analysis pipeline. For four of the closest pulsars their equatorial ellipticities were constrained to less than = 10-5 with 95% confidence. These limits are beginning to reach interesting ellipticities which some exotic theories suggest could be supported in neutron stars. The third science run (S3) in which GEO 600 and LIGO participated took place from late October 2003 to early January 2004. Again, the improvement in sensitivity compared to the previous run (S2) was significant. Preliminary multi-detector results were determined for the same previous 28 pulsars using S3 data. The equatorial ellipticities for 11 of these pulsars are constrained to less = 10-5 with 95% confidence. With the S3 data, the upper limit on the gravitational wave emission from the Crab pulsar was only approximately a factor of four from the upper limits inferred from the spindown of the pulsar. When this barrier is overcome the prospects of detecting gravitational waves from the Crab pulsar will become more plausible. Future work based on these implementations will examine a larger set of missing known pulsars including binary systems. Studies in Markov Chain Monte Carlo techniques may also allow the expansion this method to a larger parameter space.
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Hölscher, Patric [Verfasser]. "Gravitational Waves in Conformal Gravity / Patric Hölscher." Bielefeld : Universitätsbibliothek Bielefeld, 2019. http://d-nb.info/1200097653/34.
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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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Cole, Robert Harry. "Gravitational waves from extreme-mass-ratio inspirals." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709066.
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Del, Pozzo Walter. "Black Holes, Galaxy Clusters and Gravitational Waves." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1321/.
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This thesis deals with three aspects of modern astrophysical research. We propose a Bayesian data analysis framework to test alternative theories of gravity using observations of Gravitational Waves (GWs) from the inspiral phase of binary systems. We compare General Relativity predictions to the ones from a Massive Graviton theory. We can discriminate between the two theories and produce posterior probability distribution functions. We also devise a method to combine multiple observations that y increases the amount of information that is possible to extract from GWs. Using current wide-field sky survey s, in concert with the established Luminosity -- Black Hole mass relation, we calculate the mass distribution of supermassive massive black holes (SMBHs) and Active Galactic Nuclei (AGNs) in three different environments. SMBHs and radio-AGNs are concentrated in dense environments. The Black Hole Fundamental Plane predicts X-ray properties for our SMBHs and unifies modes of AGN activity in terms of the rate of accretion. Studying two-body mergers of realistic galaxy clusters, we show that these reproduce the observed metallicity distribution in the Intra Cluster Medium (ICM). We characterise entropy generation and mixing induced by the merger process.
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Bethke, Laura Bianca. "Exploring the early universe with gravitational waves." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24763.
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In this thesis, I will discuss two separate topics which are related to gravitational wave production in the early universe. The first part will focus on the tensor power spectrum from inflation, derived using the Ashtekar variables of loop quantum gravity. This formalism is different from the ordinary approach in that it uses a complex connection as the central gravitational variable instead of the metric. Although the choice of variables should not affect any classical results, it becomes vital when considering quantum mechanical quantities like vacuum fluctuations. We will find that in this formalism, the tensor power spectrum is chiral, which would lead to a non-zero TB correlator in the CMB. Obtaining the full TB power spectrum would enable us to probe this chirality and provide clues about the nature of gravity. In the second part, I will consider gravitational waves produced from massless preheating, during which the inflaton transfers energy to a scalar field chi. If chi is light, it acquires a scale invariant spectrum of perturbations from inflation. At the time of preheating, the field will therefore have fluctuations on superhorizon scales and take a different value in different parts of the observable universe. I will study GW production for different initial values of chi numerically using 3d lattice simulations. The GW amplitude strongly depends on this initial value, leading to a GW background that is anisotropic today, with relative fluctuations of order 1%. In general, anisotropies will occur in any model of preheating with a light scalar field, and the characteristics should strongly depend on the model parameters. If a GW background from preheating was measured in the future, it would provide a novel way to distinguish between different inflationary scenarios.
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Aho, Daniel, and Ask Ellingsen. "Gravitational Waves from Slow Motion Binary Systems." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210831.
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In this thesis we study gravitational waves in the domain of linearised general relativity. Wepresent the fundamental ideas and theory of general relativity, then, using the traditionalmeans of quadrupole approximation, we derive an expression for the power radiated as gravitationalwaves in a binary system. We limit ourselves to binary systems in the Newtonianlimit, and can therefore use Kepler’s laws in our calculations. We then use the derived expressionto explicitly predict the power radiated by the Sun-planet systems in our solar systemspecifically, regarding each system as a binary consisting of the planet and the Sun. Finally,we calculate the resulting orbital decay and find an expression for the time it would take forthe bodies to come into contact if gravitational radiation were the only means by which thesystem lost energy. As expected, the power radiated by gravitational waves is found to bevery small for systems in the Newtonian limit, and the corresponding time until impact isfound to be on the order of many times the age of the Universe.
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Porfyriadis, Achilleas. "Gravitational Waves From the Kerr/CFT Correspondence." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493351.
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Astronomical observation suggests the existence of near-extreme Kerr black holes in the sky. Properties of diffeomorphisms imply that dynamics of the near-horizon region of near-extreme Kerr are governed by an infinite-dimensional conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this thesis we compute the gravitational radiation emitted by a small compact object that orbits in the near-horizon region and plunges into the horizon of a large rapidly rotating black hole. We study the holographically dual processes in the context of the Kerr/CFT correspondence and find our conformal field theory (CFT) computations in perfect agreement with the gravity results.
We compute the radiation emitted by a particle on the innermost stable circular orbit (ISCO) of a rapidly spinning black hole. We confirm previous estimates of the overall scaling of the power radiated, but show that there are also small oscillations all the way to extremality. Furthermore, we reveal an intricate mode-by-mode structure in the flux to infinity, with only certain modes having the dominant scaling. The scaling of each mode is controlled by its conformal weight.
Massive objects in adiabatic quasi-circular inspiral towards a near-extreme Kerr black hole quickly plunge into the horizon after passing the ISCO. The post-ISCO plunge trajectory is shown to be related by a conformal map to a circular orbit. Conformal symmetry of the near-horizon region is then used to compute analytically the gravitational radiation produced during the plunge phase.
Most extreme-mass-ratio-inspirals of small compact objects into supermassive black holes end with a fast plunge from an eccentric last stable orbit. We use conformal transformations to analytically solve for the radiation emitted from various fast plunges into extreme and near-extreme Kerr black holes.Physics
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Singh, S., L. A. De Lorenzo, I. Pikovski, and K. C. Schwab. "Detecting continuous gravitational waves with superfluid 4He." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625336.
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Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very highQ-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For thermal noise limited sensitivity, we find that strain fields on the order of h similar to 10(-23)/root Hz are detectable. Measuring such strains is possible by implementing state of the art microwave transducer technology. Weshow that the proposed system can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for certain pulsar sources within a few months of integration time.
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Antonucci, Federica <1976>. "Search for gravitational waves from known pulsar." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2061/1/FedericaAntonucciTesiDott.FISICA.pdf.
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Antonucci, Federica <1976>. "Search for gravitational waves from known pulsar." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2061/.
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Degallaix, Jerome. "Compensation of strong thermal lensing in advanced interferometric gravitational waves detectors." University of Western Australia. School of Physics, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0060.
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A network of laser interferometer gravitational waves detectors spread across the globe is currently running and steadily improving. After complex data analysis from the output signal of the present detectors, astrophysical results begin to emerge with upper limits on gravitational wave sources. So far, however no direct detection has been announced. To increase the sensitivity of current detectors, a second generation of interferometers is planned which will make gravitational wave astronomy a reality within one decade. The advanced generation of interferometers will represent a substantial upgrade from current detectors. Especially, very high optical power will circulate in the arm cavities in order to reduce by one order of magnitude the shot noise limited sensitivity in high frequency. However, the theoretical shot noise limit will only be achieved after implementation of complex thermal lensing compensation schemes. Thermal lensing is direct consequence of the residual optical absorption inside the substrate and coating of the test masses and could have tragic consequences for the functionality of the interferometer. The Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) in collaboration with LIGO will run a series of high optical power tests to understand the characteristics and effects of thermal lensing. During these tests, techniques to compensate thermal lensing will be experimented. This thesis mainly focused on the first high optical power test in Gingin, Australia. The first test will consist of a Fabry Perot cavity with the sapphire substrate of the input mirror inside the cavity. Due to the high optical circulating power a strong convergent thermal lens will appear in the input mirror substrate. Because of the presence of the thermal lens inside the cavity, the size of the cavity waist will be reduced and the cavity circulating power will decrease. Simulations using higher order mode expansion and FFT propagation code were completed to estimate ways to compensate strong thermal lensing for the Gingin first test. The term `strong thermal lensing? is used because the thermal lens focal length is comparable to the design focal length of the optical components. The expected performance of a fused silica compensation plate is presented and advantages and limits of this method are discussed. Experimental results on small scale actuators which can potentially compensate thermal lensing are detailed. The knowledge gained from these experiments was valuable to design the real scale compensation plate which was used in the first Gingin test. This test was carried at the end of 2005. The thermal lens due to 1 kW of optical power circulating in the sapphire substrate was successfully compensated using a fused silica plate. Yet, thermal lensing compensation may only be required for room temperature advanced interferometer. Indeed, we showed that cooling the interferometer mirror to cryogenic temperature can eliminate the thermal lensing problem and also substantially decrease the mirror thermal noise.
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Servin, Martin. "Nonlinear interaction and propagation of gravitational and electromagnetic waves in plasmas." Doctoral thesis, Umeå University, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-122.
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Gravitational waves and electromagnetic waves are important as carriers of energy and information. This thesis is devoted to the study of the propagation and interaction of these waves in plasmas, with emphasis on nonlinear effects and applications within astrophysics.
The physical systems are described by the Einstein-Maxwell-fluid equations or Einstein-Maxwell-Vlasov equations, when a kinetic treatment is required. The small amplitude and high-frequency approximation is employed for the gravitational waves, such that perturbative techniques can be applied and space-time can be considered locally flat, with a gravitational radiation field superimposed on it. The gravitational waves give rise to coupling terms that have the structure of effective currents in the Maxwell equations and an effective gravitational force in the equation of motion for the plasma. The Einstein field equations describe the evolution of the gravitational waves, with the perturbed energy-momentum density of the plasma and the electromagnetic field as a source.
The processes that are investigated are gravitational waves exciting electromagnetic waves in plasmas, altering the optical properties of plasmas and accelerating charged particles. The thesis also deals with the propagation propertities of gravitational and electromagnetic waves, e.g. effects due to resonant wave-particle interactions, plasma inhomogeneties and nonlinear self-interactions. It is also shown that plasmas that are not in thermodynamical equilibrium may release their free energy by emitting gravitational waves.
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Talukder, Dipongkar. "Multi-baseline gravitational wave radiometry." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/d_talukder_112408.pdf.
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Thesis (M.S. in physics)--Washington State University, December 2008.Title from PDF title page (viewed on June 19, 2009). "Department of Physics and Astronomy." Includes bibliographical references (p. 44-46).
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Gültekin, Kayhan. "Growing intermediate-mass black holes with gravitational waves." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3749.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Astronomy. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Cetoli, Alberto. "Excitations in Superfluids : From solitons to gravitational waves." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-38914.
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In 1995 two different research groups observed for the first time the Bose-Einstein condensation (BEC) in ultracold gases. When the confining magnetic trap was turned off the gas was left free to expand, and the velocity of the particles showed a clear peak: most of the particles were occupying the same single particle state, the one of lowest energy. The Bose-Einstein condensation had been predicted in 1925 by Einstein, written by inspiration of a work on the statistic of the photons by Bose (1924). In this work Bose described the behavior of an ensemble of photons, treating them as massless particles, with no number conservation associated. Einstein extended this approach to particles with a mass and with fixed number, creating what is now called the Bose-Einstein distribution. The particles that follow such a description are called ``bosons'', as opposed to the ``fermions'' of the Fermi-Dirac statistics. Einstein predicted that in a gas of bosons - under a critical temperature - a finite fraction of the total number of particles would have been in the ground state, and act as a single entity. This amusing theoretical discovery found its utility a few years later. In the late thirties, new techniques allowed to cool Helium-4 at few Kelvins above the absolute zero. The properties of the resulting liquid were a puzzlement to the scientific community: among others, it could flow without experiencing friction. The liquid was called a ``superfluid''. A first explanation was given by London in 1938, which linked the superfluid behavior to the presence of a BEC among the bosonic Helium particles. The fermions cannot condense by themselves. On the other hand, they can form bound pairs and act as bosons, as it happens in a metal at low temperature. Using this approach, in 1957 Bardeen, Cooper and Schrieffer created a successful model of superconductivity by describing a superconductor as a superfluid in a charged system. During the course of these years we explored the superfluid properties of Bosons and Fermions in different settings. The original contributions of the thesis are described starting from the third chapter, where we speak about the generation and stability of solitons in a periodic optical lattices, both fixed or in motion. In the fourth chapter we study the generation of giant vortices in cold fermions, by using a generalized hydrodynamical approach. In chapter 5 we study the effect of a quasiperiodic lattice and the glassy phase it produces on a gas of bosons. Finally, we study the interaction of normal matter and superfluids with gravitational waves. While this interaction is seen to be extremely small, we believe that the resulting formalism is interesting by itself.
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Pereira, Rheymisson. "Gravitational Waves and the Stability of Binary Systems." Thesis, Uppsala universitet, Teoretisk fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331700.
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This project contains an exposition of the basics of General Relativity up to the study of Gravitational Waves. The goal is to apply this theory to understand binary systems, how they generate gravitational waves and the energy they lose in doing so. Gravitational waves have been a topic of interest in relativity ever since their theoretical prediction in 1916. Now the interest in the subject has been renewed since LIGO's announcement of the first detection of gravitational waves, proving once again the power of General Relativity. This topic is very promising because of its implications in the future of astronomy and cosmology as a new method to obtain information about our universe.
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Graff, Philip B. "Bayesian methods for gravitational waves and neural networks." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/244270.
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Einstein’s general theory of relativity has withstood 100 years of testing and will soon be facing one of its toughest challenges. In a few years we expect to be entering the era of the first direct observations of gravitational waves. These are tiny perturbations of space-time that are generated by accelerating matter and affect the measured distances between two points. Observations of these using the laser interferometers, which are the most sensitive length-measuring devices in the world, will allow us to test models of interactions in the strong field regime of gravity and eventually general relativity itself. I apply the tools of Bayesian inference for the examination of gravitational wave data from the LIGO and Virgo detectors. This is used for signal detection and estimation of the source parameters. I quantify the ability of a network of ground-based detectors to localise a source position on the sky for electromagnetic follow-up. Bayesian criteria are also applied to separating real signals from glitches in the detectors. These same tools and lessons can also be applied to the type of data expected from planned space-based detectors. Using simulations from the Mock LISA Data Challenges, I analyse our ability to detect and characterise both burst and continuous signals. The two seemingly different signal types will be overlapping and confused with one another for a space-based detector; my analysis shows that we will be able to separate and identify many signals present. Data sets and astrophysical models are continuously increasing in complexity. This will create an additional computational burden for performing Bayesian inference and other types of data analysis. I investigate the application of the MOPED algorithm for faster parameter estimation and data compression. I find that its shortcomings make it a less favourable candidate for further implementation. The framework of an artificial neural network is a simple model for the structure of a brain which can “learn” functional relationships between sets of inputs and outputs. I describe an algorithm developed for the training of feed-forward networks on pre-calculated data sets. The trained networks can then be used for fast prediction of outputs for new sets of inputs. After demonstrating capabilities on toy data sets, I apply the ability of the network to classifying handwritten digits from the MNIST database and measuring ellipticities of galaxies in the Mapping Dark Matter challenge. The power of neural networks for learning and rapid prediction is also useful in Bayesian inference where the likelihood function is computationally expensive. The new BAMBI algorithm is detailed, in which our network training algorithm is combined with the nested sampling algorithm MULTINEST to provide rapid Bayesian inference. Using samples from the normal inference, a network is trained on the likelihood function and eventually used in its place. This is able to provide significant increase in the speed of Bayesian inference while returning identical results. The trained networks can then be used for extremely rapid follow-up analyses with different priors, obtaining orders of magnitude of speed increase. Learning how to apply the tools of Bayesian inference for the optimal recovery of gravitational wave signals will provide the most scientific information when the first detections are made. Complementary to this, the improvement of our analysis algorithms to provide the best results in less time will make analysis of larger and more complicated models and data sets practical.
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Martel, Karl. "Signal detection of gravitational waves from eccentric binaries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ47345.pdf.
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Rapoport, Sharon S. B. Massachusetts Institute of Technology. "Towards detecting gravitational waves from the Crab Pulsar." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/51592.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Includes bibliographical references (leaf 47).
A variety of fundamental and technical noise sources impact the ability of the Laser Interferometer Gravitational-Wave Observatory (LIGO) to directly detect gravitational radiation. Noteworthy examples include Newtonian gravity gradient, seismic, acoustic, thermal and photon shot noise. These are the obstacles that must be confronted by the planned upgrade to the LIGO detectors, Advanced LIGO. To achieve improved sensitivity, significant improvements of LIGO's hardware must be paralleled by equivalent advances in the digital realm. Using adaptive filtering techniques, it is possible to cancel noise from known sources. We present results showing successful suppression of power line noise at 60Hz by a factor of 500 using commonly available sensors and standard FIR filters. Attenuation of 60Hz noise is particularly important to LIGO due to the 59.7 Hz radiation frequency of the Crab pulsar. Application of the techniques developed in this work to the LIGO detectors promises to improve the signal to noise ratio at the Crab frequency and thus pave the way toward direct detection of gravitational radiation from a known source.
by Sharon Rapoport.
S.B.
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O'Dea, Daniel Thomas. "Detecting gravitational waves with microwave background polarization measurements." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611378.
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Robinson, Craig A. K. "Searching for gravitational waves from compact binary coalscences." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54665/.
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Firstly, we give a general introduction to gravitational waves, the instruments used to detect them, potentially interesting sources, and the basics of gravitational wave data analysis with respect to the compact binary search. Following this, we look at a new class of approximants for inspiral waveforms. In these complete approximants, instead of truncating the binding energy and flux functions at the same post-Newtonian order, we instead keep terms such that the approximant corresponds in spirit to the dynamics of the system, with no missing terms in the acceleration. We compare the overlaps with an exact signal (in the adiabatic approximation) for a test mass orbiting a Schwarzchild black hole, for standard and complete approximants in the adiabatic approximation, and beyond the adiabatic approximation using Lagrangian models. A limited extension to the comparable mass case is also given. We then investigate two approaches to performing inspiral searches in a time-critical manner. Both involve splitting the search parameter space across several compute nodes. The first attempts to split the parameter space in an efficient manner by using information from previous runs. The second is balanced dynamically, with slave nodes requesting work off a master node. We then develop a new method for coincidence analysis. In this method, each trigger has associated with it an ellipsoidal region of the parameter space defined by the covariance matrix. Triggers from different detectors are deemed coincident if their ellipsoids are found to overlap. Compared to an algorithm which uses uncorrelated windows separately for each parameter, the method significantly reduces the background rate for comparable detection efficiency. We then give a summary of the current status of the ongoing search for high mass compact binary coalescences in the first calendar year of LIGOs fifth science run.
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Logue, Joshua. "Bayesian model selection with gravitational waves from supernovae." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6097/.
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This thesis concerns inferring core collapse supernova physics using gravitational waves. The mechanism through which the supernova is re-energised is not well understood and there are many theories of the physical processes behind the so called supernova mechanism. Gravitational waves provide an opportunity to see through to the core of a collapsing star. This thesis provides an algorithm that will analyse a detected gravitational waveform from a core collapse supernova and identify the supernova mechanism. This is achieved through the use of Bayesian model selection and a nested sampling algorithm. This Bayesian data analysis algorithm is called the Supernova Model Evidence Extractor (SMEE). SMEE is designed to classify detected gravitational waveforms from core-collapse supernovae and 3 different versions which employ different types of data have been developed. These 3 versions utilise time domain (which has been fast Fourier transformed into the frequency domain), power spectrum domain and spectrogram data and the success of each version is investigated. Firstly, results for a simplified idealised version of SMEE are discussed. In this scenario only a single gravitational wave detector is considered and the effect of the sky position of the source are ignored. Next, techniques which can be employed to improve SMEE are investigated. Finally, SMEE is tested using 3 gravitational wave detectors and the full effect of the time delay between detectors and the antenna response on each detector is included. As well as this, recoloured detector noise from the Science runs from both LIGO and Virgo are utilised here. This thesis demonstrates that each version of SMEE is successful and are able to infer the supernova mechanism for a galactic supernova. The spectrogram version of SMEE is deemed the most accurate and it is recommended that this technique should be further explored in the future.
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Blelly, Aurore. "Characterization of galactic binary systems by gravitational waves." Thesis, université Paris-Saclay, 2022. http://www.theses.fr/2022UPASP070.
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Le futur observatoire spatial d’ondes gravitationnelles LISA ouvrira une nouvelle fenêtre pour la mesure des ondes gravitationnelles, permettant d’observer des sources difficilement visibles avec les observatoires terrestres actuels. Parmi ces sources, la détection des binaires galactiques promet une richesse d’informations sans précédent, mais soulève également plusieurs défis d’analyse de données. En particulier, le grand nombre de sources attendues et la présence à la fois de bruit et d’artefacts entachant les données nécessitent le développement de méthodes d’analyse robustes.Grâce à une modélisation simple des signaux recherchés, nous montrons qu’il est possible de détecter les signaux en présence de bruit et de les estimer. Nous expliquons ensuite comment ce modèle peut être utilisé pour atténuer efficacement l’impact des données manquantes sur l’analyse. Enfin, nous étudierons ce qu’un nouveau modèle appris peut apporter en termes de caractérisation du signalThe forthcoming space-based gravitational wave observatory LISA will open a new window for the measurement of gravitational waves, making it possible to observe emitting systems hardly visible with the current Earth-based observatories. Among these sources, the detection of galactic binaries promises an unprecedented wealth of information about these systems, but also raises several challenges in signal processing. In particular the large number of expected sources and the presence of both complex instrumental noise and artifacts tainting the data call for the development of robust methods. Through simple modeling of the sought signals, we show that it is possible to detect them accurately in presence of instrumental noise and to recover the signals. We then explain how this model can be used to efficiently mitigate the impact of missing data on the analysis. Finally, we investigate what a new learning-based model can bring in terms of signal characterization
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Majstorović, Josipa. "Influence of gravitational waves on Earth normal modes." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAH011.
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Nous avons révisé et développé une modélisation analytique de l’interaction des ondes gravitationnelles avec la Terre en termes d’excitation des modes propres. Nous avons, dans un premier temps, réévalué la réponse d’une Terre sphérique, sans rotation et radialement stratifiée à des sources d’ondes gravitationnelles monochromatiques en termes de déplacement radial induit à la surface. Nous avons ensuite développé une nouvelle solution pour une Terre en rotation, ellipsoïdale et latéralement hétérogène. Nous avons considéré comme sources d’ondes gravitationnelles les systèmes binaires de naines blanches. Dans les deux cas, les seuls modes propres qui sont excités sont les modes quadripolaires. La réponse finale dépend fortement de la fréquence de l’onde gravitationnelle, la plus grande excitation étant à résonance avec des modes propres. Cependant, la détection de ces faibles signaux dans des données gravimétriques ou sismologiques est très difficile de par la présence d’un bruit trop élevé dans ces observations et ce même après l’utilisation de techniques de traitement du signal, comme le filtrage adaptatif. La réponse de la Terre en termes d’excitation des modes propres est dix ordres de grandeur plus faible que le niveau de bruit ambiant sur Terre. Finalement, nous avons mis en évidence certaines limites d’outils de traitement du signal utilisés pour la recherche et l’analyse de petits signaux. En particulier, la distribution des stations à la surface du globe peut introduire des biais dans l’étude des modes propresWe have revisited and developed an analytical model of the interaction between the gravitational waves and the Earth in terms of normal modes excitation. We have first reevaluated the induced response for a spherical, radially heterogeneous and non-rotating model to monochromatic gravitational wave sources in terms of radial displacement at the Earth’s surface. Then we have developed a new analytical solution for a rotating elliptical model with lateral heterogeneities. We have considered sources of the gravitational waves that are the double white-dwarf binary systems. We have shown that for both models the only normal modes that are being excited are the quadrupole ones. The final responses highly depend on the gravitational wave frequencies, the largest response being at resonance with a normal mode. However, the detection of these elusive signals in gravimetric and seismological data is very difficult due to large environmental noise present in the data, even after using some signal processing techniques like the matched filtering. There are ten orders of magnitude difference between the calculated Earth’s normal modes response and the ambient noise level. Finally, we have highlighted some limitation of the signal processing techniques used for the search and analysis of the weak signals. In particular, some biases can be introduced when using different station distributions at the surface of the globe in the frame of normal mode studies
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Kim, Yunho. "Quadratic Gravity with Black Holes and Gravitational Waves." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/26707.
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This thesis investigates black holes and gravitational waves in the framework of quadratic gravity. These subjects are introduced by first examining the current state of general relativity and how it is realised. The discussion then addresses the quantitative aspects of black holes, gravitational waves, and quadratic gravity. This is then followed by the exploration of the three main research topics.
The first research topic investigates the induced charging of a black hole due to a topological term in quadratic gravity. The second research topic focuses on the approximate analytic non-Schwarzschild black hole solutions in quadratic gravity. Finally, gravitational waves generated by binary systems within quadratic gravity are studied, with a focus on the corrections produced by the massive scalar field and the massive spin-2 field.