Dissertations / Theses on the topic 'Astroparticle physics and particle cosmology'
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Scott, Pat. "Searches for Particle Dark Matter Dark stars, dark galaxies, dark halos and global supersymmetric fits /." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38221.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted. Härtill 6 uppsatser.
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Strid, Carl-Fabian. "MAC-E-Filter characterization for PTOLEMY : a relic neutrino direct detection experiment." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75678.
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The cosmic neutrino background (CNB) can be composed of both active and hypothetical sterileneutrinos. At approximately one second after big bang, neutrinos decoupled from radiationand matter at a temperature of approximately one MeV. Neutrinos played an important role inthe origin and evolution of our universe and have been indirectly verified by cosmological dataon the BBN (Big Bang nucleosynthesis) of the Big Bang.It was Steven Weinberg in 1962 that first theorized on the direct detection of relic neutrinos.The signal of the relic neutrino capture on a tritium target can be observed by studying theendpoint of the electrons kinetic energy that are above the endpoint energy of the beta decayspectrum. The PTOLEMY project aims to archive direct detection of the relic neutrinobackground with a large tritium target of 100 gram, MAC-E-Filter, RF-tracking, Time of flighttracking and a cryogenic calorimetry.In this thesis the MAC-E-Filter have been simulated in two filter configurations. In the firstconfiguration, the electron were simulated five times in the filter. Two in the opposite sideof the detector, one in the middle, and two at the detector. In the second configuration theelectrons was simulated in the entrance solenoid at a fixed position of y = -0.19634954 m fromthe center of the filter and in random positions. Both multiple electrons and single electronswere simulated in the second configuration.In the single electron configuration the electron had a starting position of y = -0.19634954 mfrom the center of the filter, and an initial kinetic energy of 18.6 KeV. The first filter configurationsuccessfully accomplished to simulate the electron track, as the electron was reflectedback and forth between the entry and detector solenoid. The electric and magnetic field profilediered at the entry and detector solenoid. The second filter configuration successfully showedthat the electron will reach the end solenoid, when the filter length was 0.5 m. When the filterlength was increased to 0.7 m, then the electron was reflected in the middle of the filter. Thesimulation showed that the electron energy dropped below 1 eV from 18.6 KeV as the electronpropagated through the filter. The magnetic and electric fields decreased exponentially in thedirection of the detector solenoid. The Simulation of multiple electrons showed mixed resultsand would need more modifications in order to come to a final conclusion.
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Birkel, Michael. "Astroparticle physics beyond the standard model." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388826.
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Nasri, Salah Schechter Joseph. "Neutrinos in particle physics and cosmology." Related Electronic Resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2003. http://wwwlib.umi.com/cr/syr/main.
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Kaplinghat, Manoj. "Constraints on particle physics from cosmology /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488191667179811.
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Nunes, Nelson. "Attractor solutions in cosmology and particle physics." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247958.
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Salem, Michael Phillip Wise Mark B. "Topics in theoretical particle physics and cosmology /." Diss., Pasadena, Calif. : California Institute of Technology, 2007. http://resolver.caltech.edu/CaltechETD:etd-05222007-105100.
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Martineau, Patrick. "On particle production and brane cosmology." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80328.
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Particle production is examined within the context of brane cosmology. Non-perturbative formalisms are reviewed and employed to calculate particle number (or the energy density associated with such particles) produced in dynamical spacetimes arising from various brane configurations. Specifically, reheating from tachyon condensation, the quantum instability of a class of S-brane spacetimes, and particle production on an orbiting brane-antibrane system are investigated.
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Dai, De-Chang. "Modified Gravity in Cosmology and Fundamental Particle Physics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1207065832.
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Lucente, Michele. "Implication of Sterile Fermions in Particle Physics and Cosmology." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112210/document.
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Le mécanisme de génération de masses des neutrinos, la nature de la matière noire et l’origine de l’asymétrie baryonique de l’Univers sont les trois questions les plus pressantes dans la physique moderne des astroparticules, qui exigent l’introduction d’une nouvelle physique au-delà du Modèle Standard. Dans cette thèse, nous nous concentrons sur ces trois questions en fournissant une solution possible en termes d'une extension minimale du Modèle Standard, constituée par l’ajout d'un ensemble de fermions stériles au contenu des champs de la théorie. Les fermions stériles sont des champs qui sont singlets de jauge et qui peuvent interagir avec les neutrinos actifs à travers des termes de mélange. Nous nous concentrons sur le mécanisme dit de l’Inverse Seesaw (ISS), qui est caractérisé par une faible échelle de la nouvelle physique (de l’ordre TeV ou inférieure) et qui peut être testé dans les installations expérimentales actuelles et futures. Nous présentons l'analyse qui permet d’identifier les réalisations minimales de ce mécanisme et l'étude phénoménologique pour prendre en compte la masses des neutrinos légers et pour imposer toutes les contraintes expérimentales pertinentes au modèle, ainsi que les signatures expérimentales attendues. Nous montrons la viabilité de l’hypothèse que les neutrinos stériles constituent la matière noire, et les caractéristiques de cette solution dans le mécanisme minimale de l’ISS. La possibilité d’expliquer avec succès l'asymétrie baryonique à travers un processus de leptogenèse dans une réalisation testable du mécanisme est aussi adressée. Il est important de chercher des manifestations des fermions stériles dans les expériences de laboratoire. Nous abordons ce point en faisant des prévisions sur les rapports des branchement attendus pour les désintégrations des bosons vectoriels qui violent le saveur leptonique, qui peuvent être véhiculés par les fermions stériles. Nous étudions aussi l'impact des fermions stériles sur les fits globaux des données de précision électrofaibleThe neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We show the viability of the sterile neutrino hypothesis as dark matter component, together with the characteristic features of this scenario in the minimal Inverse Seesaw mechanism. The possibility of successfully accounting for the baryon asymmetry in a testable realisation of the leptogenesis mechanism is also addressed.On the other side it is important to look for manifestations of sterile fermions in laboratory experiments. We address this point by making predictions for the expected rates of rare lepton number violating decays of vector bosons, that can be mediated by sterile fermions, as well as by studying the impact of sterile fermions on global fit of electroweak precision data
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Lin, Tongyan. "Signals of Particle Dark Matter." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10273.
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This thesis explores methods of detecting dark matter particles, with some emphasis on several dark matter models of current interest. Detection in this context means observation of an experimental signature correlated with dark matter interactions with Standard Model particles. This includes recoils of nuclei or electrons from dark matter scattering events, and direct or indirect observation of particles produced by dark matter annihilation.Physics
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Pongkitivanichkul, Chakrit. "Aspects of particle physics and cosmology from string/M theory." Thesis, King's College London (University of London), 2016. https://kclpure.kcl.ac.uk/portal/en/theses/aspects-of-particle-physics-and-cosmology-from-stringm-theory(c5c9c1b1-8af3-4669-b507-ed3926ef4515).html.
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This thesis is focused on various aspects of particle physics and cosmology from String/M theory. Assuming our universe is a solution of string/M theory, physics below the unication scale is an eective 4D supergravity theory with an abundance of moduli and axions. The phenomenology of moduli and axions in an early universe is studied. We particularly study dark radiation constraints on a generic Axiverse scenario and provide various solutions to it. The simplest solution requires the lightest modulus decays only into its own axion superpartner and this severely constrains the moduli Kahler potential and mass matrix. We also study a model building aspect of string/M theory. It has been shown that a discrete symmetry on a manifold with G2 holonomy combined with symmetry breaking Wilson lines provide a solution to the doublet-triplet splitting problem. We extend the idea to a new class of model based on M theory compactied on a G2 manifold which leads to a novel solution where the colour triplets are decoupled. The models also involves an extra vector-like standard model multiplet to restore gauge unication. We will also discuss the phenomenology of the new light states and the induced R-parity violation. We will also study the prospects of searches from a future generation of colliders. We focus in particular on the search at a 100 TeV collider via the WZ channel. The motivation from string/M theory models leads to the assumption that Higgsinos form the lightest supersymmetric particle. We design simple signal regions for the trilepton channel and nd that neutralinos-charginos could be discovered(excluded) up to 1.1 (1.8) TeV.
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Jenkins, Alejandro Wise Mark B. "Topics in particle physics and cosmology beyond the standard model /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-06022006-145211.
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Marsh, David J. E. "The string axiverse and cosmology." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:74063b60-5ede-4205-88d5-b5cbab0b3d1d.
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This thesis studies the cosmology of ultra-light scalar fields with masses in the range 10−33 eV ? m ? 10−18 eV and their effects on cosmology. The existence of such fields is motivated by the theoretical framework of the "String Axiverse". All types of string theory contain multiple axion fields associated with antisymmetric tensor fields compactified on closed cycles in the compact space. Since the masses of these fields scale exponentially with the volume of the cycle, it is possible for them to be naturally light. We study the effects of these fields as a component of the dark matter and show analytically and numerically that they cause a suppression of structure formation on cosmological scales set by the inverse mass. We show that it will be possible with future galaxy redshift and weak lensing surveys to detect an ultra- light field comprising of order a percent of the total dark matter. If such a field is allowed to couple to the geometry that provided its mass via a phenomenological scalar potential for the axion and modulus, then the expansion of the universe can be altered significantly. In particular, we find that it is possible to have multiple epochs of accelerated expansion over a large region of parameter space, and to have a flat universe with a big crunch in the distant future. Finally, we address the issue of isocurvature perturbations in axion cosmologies, and demonstrate that in the ultra-light case the power spectrum is effected. This may have implications for the conclusions made about fine tuning in the axiverse in relation to a potential detection of tensor modes in the CMB that are different to the case of a standard axion.
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Ng, Yifung. "It’s All About Electromagnetism – From Magnetic Monopoles to Cosmological Magnetic Fields." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1291413218.
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Thompson, Rodger. "The Relation between Fundamental Constants and Particle Physics Parameters." MDPI AG, 2017. http://hdl.handle.net/10150/624359.
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The observed constraints on the variability of the proton to electron mass ratio and the fine structure constant are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and the Yukawa couplings. Further model dependent assumptions provide constraints on the Higgs VEV and the Yukawa couplings separately. A primary conclusion is that limits on the variability of dimensionless fundamental constants such as and provide important constraints on the parameter space of new physics and cosmologies.
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Wiegand, Alexander [Verfasser]. "The inhomogeneous Universe : its average expansion and cosmic variance / Alexander Wiegand. Fakultät für Physik - Cosmology and Astroparticle Physics." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1026077605/34.
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Niblaeus, Carl. "The Sun as a laboratory for particle physics." Licentiate thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-143334.
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In the paper attached to this thesis, Paper I, we have calculated the flux of neutrinos that emanate from cosmic ray collisions in the solar atmosphere. These neutrinos are created in the cascades that follow the primary collision and can travel from their production point to a detector on Earth, interacting with the solar material and oscillating on the way. The motivation is both a better understanding of the cosmic ray interactions in the solar environment but also the fact that this neutrino flux presents an almost irreducible background for the searches for neutrinos from annihilations between dark matter particles in the Sun’s core. This interesting connection between neutrinos and dark matter make use of the Sun as a laboratory to investigate new models of particle physics. If dark matter consists of weakly interacting massive particles (WIMPs), the Sun will sweep up some of these WIMPs when it moves through the halo of dark matter that our galaxy lies in. These WIMPs will become gravitationally bound to the Sun and over time accumulate in the Sun’s core. In most models WIMPs can annihilate to Standard Model particles when encountering each other. The only particle that can make it out of the Sun without being absorbed is the neutrino. The buildup of WIMPs in the solar interior can therefore lead to a detectable flux of neutrinos. Neutrino telescopes therefore search for an excess of neutrinos from the Sun. To be able to ensure that a detected flux is in fact coming from dark matter annihilations one must properly account for all other sources of neutrinos. At higher energies these are primarily neutrinos created in energetic collisions between cosmic rays and particles in the Earth’s atmosphere, but also the solar atmospheric neutrinos. The latter will be tougher to disentangle from a WIMP signal since they also come from the Sun. We calculate in Paper I the creation of the neutrinos in the solar atmosphere and propagate these neutrinos to a detector on Earth, including oscillations and interactions in the Sun and vacuum oscillations between the Sun and the Earth. We find that the expected flux is small but potentially detectable by current neutrino telescopes, although further studies are needed to fully ascertain the possibility of discovery as well as how to properly disentangle this from a potential WIMP-induced neutrino signal.
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Strobl, Karl. "Aspects of approximate symmetry in cosmology and nematic liquid crystals." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388483.
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Eyton-Williams, Oliver John. "Small Yukawa couplings in particle physics and cosmology from Type 1 string theory." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433940.
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Heurtier, Lucien. "Particle physics and Cosmology beyond the Standard Model : Inflation, Dark Matter and Flavour." Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01176578/document.
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Cette thèse se concentre sur l’étude des aspects de la physique au delà du modèle standard et de ses applications à la cosmologie. Depuis les temps reculés de l’évolution de l’Univers, jusqu’à la supersymétrie de basse énergie et à la phénoménologie des accélérateurs, des travaux variés ont été réalisés utilisant pour la majeure partie une formulation de basse énergie, et ce à des stades différents de l’Histoire de l’Univers. En effet, des modèles d’inflation sont présentés sous l’angle de théories effectives (à un champs) provenant de théories de hautes énergies issues de la supergravité et de la théorie des cordes. De plus, des modèles de matière noire incluant la présence d’une particule médiatrice sont étudiés à l’aide d’opérateurs effectifs de dimensions supérieures, générés explicitement à partir d’une théorie microscopique sous-jacente. De tels modèles semblent expliquer de récentes mesures du spectre de rayons X mesuré dans certains cluster de galaxies. Enfin l’étude des changements de saveurs dans l’extension supersymétrique incluant des jauginos de Dirac du modèle standard prédit des signatures expérimentales qui seront très probablement recherchées lors des prochaines acquisitions du LHCThis thesis has been focusing on beyond the Standard Model aspects of particle physics and their implication in cosmology. From the early times of the universe evolution, to current low energy supersymmetry and colliders phenomenology, various works have been achieved using mostly an effective, low energy formulation, at several different periods of the Universe History. Namely, models of Inflation are presented as effective single field theories arising from supergravity, string inspired UV completion models. Furthermore, models of dark matter including a mediator particle are studied with the use of effective higher dimensional operators that are generated explicitly from microscopic underlying theories. Such models were able to produce interesting results for explaining recent measurements on the X-rays spectrum of galaxy clusters. Finally, the study of flavour changing processes in the Dirac gaugino supersymmetric extensions of the Standard Model was explored in details, predicting some challenging signatures that are to be searched for at the next run of the LHC
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Gil, Pedro Francisco M. S. V. "On moduli stabilisation and cosmology in type IIB flux compactifications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:6c3ef85d-df3b-42c6-846d-a4bfdeec85de.
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This Thesis studies some aspects of string compactifications with particular em- phasis on moduli stabilisation and cosmology. In Chapter 1 I motivate the study of string compactifications as a way to build on the successes of the Standard Model of Particle Physics and of the theory of General Relativity. Chapter 2 constitutes an overview of the technical background necessary for the study of flux compactifications. I sketch how the desire to obtain a supersymmet- ric theory in four dimensions constrains us to consider compactifications of the ten dimensional theory in six dimensional Calabi-Yau orientifolds. I argue that it is strictly necessary to stabilise the geometry of this compact space in order to have a phenomenologically viable four dimensional theory. I introduce the large volume scenario of type IIB compactifications that successfully incorporates fluxes and sub- leading corrections to yield a four dimensional theory with broken supersymmetry and all geometrical moduli stabilised. The next four Chapters are devoted to the study of some phenomenological aspects of moduli stabilisation and constitute the original work developed for this Thesis. In Chapter 3 I investigate the consequences of field redefinitions in the stabilisation of moduli and supersymmetry breaking, finding that redefinitions of the small blow- up moduli do not significantly alter the standard picture of moduli stabilisation in the large volume scenario and that the soft supersymmetry breaking terms are generated at the scale of the gravitino mass. Chapter 4 deals with the putative destabilisation of the volume modulus by very dense objects. The analysis of the moduli potential shows that even the densest astrophysical objects cannot destabilise the moduli, and that destabilisation is only achievable in the context of black hole formation and cosmological singularities. In Chapter 5 I present a model of inflation within the large volume scenario. The inflaton is identified with a geometric modulus, the fibre modulus, and its potential generated by poly-instanton effects. The model is shown to be robust and consistent with current observational constraints. In Chapter 6 I introduce a model of quintessence, where the quintessence field and its potential share the same origin with the inflationary model of the previous Chapter. This model constitutes a stringy realisation of supersymmetric large extra dimensions, where supersymmetry, the low gravity scale and the scale of dark energy are intrinsically connected. I conclude in Chapter 7 outlining the direction of future research.
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Bartrum, Sam John Richard. "Scalar fields : fluctuating and dissipating in the early Universe." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/11760.
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It is likely that the early Universe was pervaded by a whole host of scalar fields which are ubiquitous in particle physics models and are employed everywhere from driving periods of accelerated expansion to the spontaneous breaking of gauge symmetries. Just as these scalar fields are important from a particle physics point of view, they can also have serious implications for the evolution of the Universe. In particular in extreme cases their dynamical evolution can lead to the failure of the synthesis of light elements or to exceed the dark matter bound in contrast to observation. These scalar fields are not however isolated systems and interact with the degrees of freedom which comprise their environment. As such two interrelated effects may arise; fluctuations and dissipation. These effects, which are enhanced at finite temperature, give rise to energy transfer between the scalar field and its environment and as such should be taken into account for a complete description of their dynamical evolution. In this thesis we will look at these effects within the inflationary era in a scenario termed warm inflation where amongst other effects, thermal fluctuations can now act as a source of primordial density perturbations. In particular we will show how a model of warm inflation based on a simple quartic potential can be brought back into agreement with Planck data through renormalizable interactions, whilst it is strongly disfavoured in the absence of such effects. Moving beyond inflation, we will consider the effect of fluctuation-dissipation dynamics on other cosmological scalar fields, deriving dissipation coefficients within common particle physics models. We also investigate how dissipation can affect cosmological phase transitions, potentially leading to late time periods of accelerated expansion, as well as presenting a novel model of dissipative leptogenesis.
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Atkins, Michael. "Bounds on the effective theory of gravity in models of particle physics and cosmology." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/47195/.
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The effective theory of gravity coupled to matter represents a fully consistent low energy theory of quantum gravity coupled to the known particles and forces of the standard model. In recent years this framework has been extensively used to make physical predictions of phenomena in high energy physics and cosmology. In this thesis we use theoretical tools and experimental data to place constraints on various popular models which utilise this framework. We speciffically derive unitarity bounds in grand unified theories, models of low scale quantum gravity, models with extra dimensions and models of Higgs inflation. We also derive a bound on the size of the Higgs boson's non-minimal coupling to gravity. This represents an important area of research because it helps us to better understand the theories and models that many physicists are currently working on and crucially it can inform us where we can reliably use the effective theory approach and where it breaks down.
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Stref, Martin. "Dark Matter on the Galactic Scale : from Particle Physics and Cosmology to Local Properties." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS077/document.
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Identifier la nature de la matière sombre est l'un des plus grands problèmes de la physique contemporaine. Si la matière sombre est constituée de particules, on peut espérer la détecter, directement ou indirectement, grâce à des expériences terrestres ou spatiales. Prédire les résultats de ces expériences, ou les interpréter en cas de détection, nécessite une compréhension profonde de la structuration de la matière sombre dans notre Galaxie. En partant de considérations issues de la physique des particules et de la cosmologie, je construits un modèle du halo de matière sombre Galactique contraint dynamiquement qui incorpore une description détaillée des ses inhomogénéités. L'impact des ces inhomogénéités sur les recherches utilisant le rayonnement cosmique est ensuite analysé en détails. J'étudie également une méthode permettant de prédire la distribution dans l'espace des phases des particules de matière sombre, et discute sa possible application aux recherches de matière sombre. Cet outil est ensuite appliqué aux recherches utilisant les électrons et positrons cosmiques, et de nouvelles contraintes très fortes sont obtenues sur les modèles microscopiques de matière sombreUnderstanding the nature of dark matter is one of the greatest challenges of modern physics. If dark matter is made of particles, we can hope to detect it, directly or indirectly, using Earth-based or spatial experiments. Make predictions for the outcome of these experiments, or interpret the results in case of a detection, requires a deep understanding of the structuring of dark matter in our Galaxy. Starting from particle physics and cosmological considerations, I built a dynamically constrained model of the Galactic dark halo including a detailed description of its inhomogeneities. The impact of these inhomogeneities on searches with cosmic rays is then analysed in details. I also study a method allowing to predict the phase-space distribution of dark matter particles, and discuss its possible application to dark matter searches. This method is then applied to searches with cosmic-ray electrons and positrons, and new very stringent constraints are obtained on microscopic models of dark matter
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Kahlhoefer, Felix Karl David. "Complementarity of searches for dark matter." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ec5b1afe-b75c-44d9-9dad-e0d342e46fa1.
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The striking evidence for the existence of dark matter in the Universe implies that there is new physics to be discovered beyond the Standard Model. To identify the nature of this dark matter is a key task for modern astroparticle physics, and a large number of experiments pursuing a range of different search strategies have been developed to solve it. The topic of this thesis is the complementarity of these different experiments and the issue of how to combine the information from different searches independently of experimental and theoretical uncertainties. The first part focuses on the direct detection of dark matter scattering in nuclear recoil detectors, with a special emphasis on the impact of the assumed velocity distribution of Galactic dark matter particles. By converting experimental data to variables that make the astrophysical unknowns explicit, different experiments can be compared without implicit assumptions concerning the dark matter halo. We extend this framework to include annual modulation signals and apply it to recent experimental hints for dark matter, showing that the tension between these results and constraints from other experiments is independent of astrophysical uncertainties. We explore possible ways of ameliorating this tension by changing our assumptions on the properties of dark matter interactions. In this context, we propose a new approach for inferring the properties of the dark matter particle, which does not require any assumptions about the structure of the dark matter halo. A particularly interesting option is to study dark matter particles that couple differently to protons and neutrons (so-called isospin-violating dark matter). Such isospin-violation arises naturally in models where the vector mediator is the gauge boson of a new U(1) that mixes with the Standard Model gauge bosons. In the second part, we first discuss the case where both the Z' and the dark matter particle have a mass of a few GeV and then turn to the case where the Z' is significantly heavier. While the former case is most strongly constrained by precision measurements from LEP and B-factories, the latter scenario can be probed with great sensitivity at the LHC using monojet and monophoton searches, as well as searches for resonances in dijet, dilepton and diboson final states. Finally, we study models of dark matter where loop contributions are important for a comparison of LHC searches and direct detection experiments. This is the case for dark matter interactions with Yukawa-like couplings to quarks and for interactions that lead to spin-dependent or momentum suppressed scattering cross sections at tree level. We find that including the contribution from heavy-quark loops can significantly alter the conclusions obtained from a tree-level analysis.
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Smirnov, Juri [Verfasser], and Manfred [Akademischer Betreuer] Lindner. "Effects of the Quantum Vacuum in Particle Physics and Cosmology / Juri Smirnov ; Betreuer: Manfred Lindner." Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1180300599/34.
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Casey, James David. "Search for high energy GRB neutrinos in IceCube." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53839.
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The IceCube Neutrino Observatory has reported the observation of 35 neutrino events above 30 TeV with evidence for an astrophysical neutrino flux using data collected from May 2010 to May 2013. These events provide the first high-energy astrophysical neutrino flux ever observed. The sources of these events are currently unknown. IceCube has looked for correlations between these events and a list of TeV photon sources including a catalog of 36 galactic sources and 42 extragalactic sources, correlations with the galactic plane and center, and spatial and temporal clustering. These searches have shown no significant correlations. The isotropic distribution of the event directions gives indications that the events could be extragalactic in nature and therefore may originate in the same processes that generate ultra-high-energy cosmic rays (UHECRs). The sources of these UHECRs are still unknown; however, gamma-ray bursts (GRBs) have been proposed as one possible source class. By determining the source of these high-energy neutrinos, it may be possible to determine the sources of UHECRs as well. This study is a search for directional and temporal correlation between 856 GRBs and the astrophysical neutrino flux observed by IceCube. Nearly 10,000 expanding time windows centered on the earliest reported time of the burst were examined. The time windows start at ±10 s and extend to ±15 days. We find no evidence of correlations for these time windows and set an upper limit on the fraction of the astrophysical flux that can be attributed to the observed GRBs as a function of the time window. GRBs can contribute at most 12% of the astrophysical neutrino flux if the neutrino-GRB correlation time is less than ≈20 hours, and no more than 38% of the astrophysical neutrino flux can be attributed to the known GRBs at time scales up to 15 days. We conclude that GRBs observable by satellites are not solely responsible for IceCube’s astrophysical neutrino flux, even if very long correlation time scales are assumed.
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Angus, Stephen Andrew. "Phenomenology of dark radiation and string compactifications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:739ffcb2-bf9d-4fd3-8d6c-911d2d599f5e.
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In this Thesis I explore aspects of dark radiation and its role in String Phenomenology. Dark radiation is any additional hidden type of relativistic matter present in the Universe today, conventionally labelled as an "excess effective number of neutrino species", Δ Neff. It provides a powerful test of hitherto untested theoretical models based on fundamental theories such as String Theory. I begin by considering dark radiation in the LARGE Volume Scenario, a phenomenologically viable class of string compactifications. First I review how the minimal setup slightly overproduces axionic dark radiation via modulus decay. I then demonstrate that loop corrections to the main competing visible-sector decay process have a negligible effect and are unable to alleviate the tension with observations. In the following chapter I explore fibred extensions of the LARGE Volume Scenario. The predictions for Δ Neff are qualitatively different: in particular, models with a sequestered visible sector on D3 branes at a singularity are swamped by massless axions and decisively ruled out. I then consider TeV-scale supersymmetry in a model with anisotropic modulus stabilisation. If the Standard Model is realised on D7 branes wrapping the small volume cycle a hierarchy of soft terms is generated, which may have applications to natural supersymmetry. The final chapter takes a different approach and investigates the proposition that dark radiation, in the form of a Cosmic Axion Background, could explain the long-standing soft X-ray excess from galaxy clusters. I show for the Coma cluster that the morphology of the excess can be reproduced by axion-photon conversion in the intracluster magnetic field, provided the field is allowed to have more structure on smaller scales than typically assumed based on Faraday rotation data. This explanation requires an inverse axion-photon coupling M ∼ 1011 - 1012 GeV and a mean axion energy (ECAB) ∼ 50 - 250 eV.
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Maia, Jackson Max Furtunato. "Algumas Aplicações de Campos Escalares em Cosmologia." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43132/tde-08112013-150636/.
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Três aplicações de campos escalares a cosmologias homogêneas e isotrópicas são apresenta- das, com motivações e resultados diversos. No primeiro caso, uma técnica de multiplicadores de Lagrange é usada para estabelecer vínculos físicos sobre os invariantes de curvatura possivelmente presentes na ação efetiva de baixas energias da teoria de cordas. Um modelo não-singular é obtido em um caso partícula, sugerindo uma possível correção na ação da gravitação compatível com as simetrias das cosmologias de cordas. Numa outra abordagem, é proposto um modelo fenomenológico não-singular baseado no decaimento do termo cosmológico. O modelo tem como principal característica uma passa- gem suave entre uma fase inflacionária do tipo de Sitter e uma fase com dinâmica do tipo Friedmann-Robertson-Walker. Como último exemplo é considerado um campo escalar acoplado termicamente ao fluido cósmico. Adotando um termo dissipativo específico, mas usual, é definido um espaço de parâmetros contendo as cosmologias com campos escalares mais comuns e o modelo padrão como casos particulares. As condições de rolamento lento são obtidas e é apresentado um modelo cosmológico simples para exemplificar o potencial heurístico dos parâmetros propostos.Three applications of scalar fields to homogeneous and isotropic cosmologies are presented, with distinct motivations and resuIts. In the first case, a Lagrange multiplier technique is used in order to set physical constraints on the curvature invariants possibly present in the low energy effective action of string theory. In a particular case, a nonsingular model is obtained, suggesting a possible correction in the gra- vity action which is compatible to the symmetries of string cosmology. In another approach, a nonsingular model based on the decay of the cosmological term is pro- posed. The model has as a major feature a smooth transition between an inflationary de Sitter phase and a phase with FRW-type dynamics. As a last example, a scalar field thermally coupled to the cosmic fluid is considered. By adop- ting a specific but usual dissipative term, it is defined a parameter space encompassing the most common scalar field cosmologies, as well as the standard model, as limiting cases. Slow roll conditions are obtained and it is presented a simple toy model to illustrate the heuristic potential of the proposed parameters.
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Matas, Andrew. "Foundations of Massive Gravity." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1464275510.
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Akrami, Yashar. "Supersymmetry vis-à-vis Observation : Dark Matter Constraints, Global Fits and Statistical Issues." Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-57194.
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Weak-scale supersymmetry is one of the most favoured theories beyond the Standard Model of particle physics that elegantly solves various theoretical and observational problems in both particle physics and cosmology. In this thesis, I describe the theoretical foundations of supersymmetry, issues that it can address and concrete supersymmetric models that are widely used in phenomenological studies. I discuss how the predictions of supersymmetric models may be compared with observational data from both colliders and cosmology. I show why constraints on supersymmetric parameters by direct and indirect searches of particle dark matter are of particular interest in this respect. Gamma-ray observations of astrophysical sources, in particular dwarf spheroidal galaxies, by the Fermi satellite, and recording nuclear recoil events and energies by future ton-scale direct detection experiments are shown to provide powerful tools in searches for supersymmetric dark matter and estimating supersymmetric parameters. I discuss some major statistical issues in supersymmetric global fits to experimental data. In particular, I further demonstrate that existing advanced scanning techniques may fail in correctly mapping the statistical properties of the parameter spaces even for the simplest supersymmetric models. Complementary scanning methods based on Genetic Algorithms are proposed.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.
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Henz, Tobias [Verfasser], and Jan Martin [Akademischer Betreuer] Pawlowski. "Physics on all Scales : Scalar-Tensor Theories of Quantum Gravity in Particle Physics and Cosmology / Tobias Henz ; Betreuer: Jan Martin Pawlowski." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180614623/34.
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Mütter, Andreas [Verfasser], Andreas [Akademischer Betreuer] Weiler, Andreas [Gutachter] Weiler, and Alejandro [Gutachter] Ibarra. "Cosmology and Particle Physics in Heterotic Orbifolds / Andreas Mütter ; Gutachter: Andreas Weiler, Alejandro Ibarra ; Betreuer: Andreas Weiler." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1220321265/34.
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Kronberg, Nico. "Exploring the parameter space of warm inflation." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/22841.
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Warm inflation is an implementation of exponential early-universe expansion that incorporates interactions between the inflaton field and its environment. These interactions allow the inflaton to dissipate some of its energy into other fields, which may then thermalise and form a radiation bath. A radiation bath present throughout inflation changes the inflaton dynamics and introduces thermal fluctuations that enhance the spectrum of primordial density perturbations. In the models we consider, the inflaton decays into the light particles of the radiation bath via heavy mediator particles. Warm inflation is subject to a complicated set of constraints which typically requires a large number of such mediator fields to be included in the model. The motivation for this work was to use the parametric dependence of the full low-temperature dissipation coefficient to uncover regimes where this number can be reduced. Previous studies have examined primarily the low-momentum regime of the dissipation coefficient, where inflaton dissipation occurs via off-shell mediator particles. In the low-temperature regime, the production of on-shell mediators in the so-called pole regime suffers from Boltzmann suppression and was therefore thought to be negligible. It has been found, however, that the exponential suppression can be compensated by a sufficiently small effective coupling between the mediator fields and the light fields. In this thesis, we present a numerical code that scans the parameter space of warm-inflation models including both the low-momentum and the pole contribution to the dissipation coefficient. We generate random values for the parameters of the model and the initial conditions of the field and the radiation density; we then solve the full equations of motion for the radiation density and the inflaton field using the general low-temperature dissipation coefficient. Our search includes chaotic, hybrid, and hilltop models, each of which inhabits different regions of warm-inflation parameter space. Our main finding is that the pole contribution to inflaton dissipation significantly extends the parameter ranges accessible to warm inflation. Specifically, we can achieve 50 e-folds of inflation and a spectral index compatible with Planck data with fewer mediator fields and smaller coupling constants. For instance, while low-momentum-dominated dissipation typically requires O(10⁶) mediator fields, we find pole-dominated solutions with as few as O(10⁴) for the quadratic hilltop potential. It is clear that the inclusion of the pole contribution opens up interesting model-building possibilities and that the parametric dependence of the full dissipation coefficient holds promise for achieving even greater reductions of the field content.
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Kulkarni, Suchita C. [Verfasser]. "Combining theory and observations : a sample study of the interplay between cosmology and particle physics / Suchita C. Kulkarni." Bonn : Universitäts- und Landesbibliothek Bonn, 2011. http://d-nb.info/1016181124/34.
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Lundström, Erik. "Phenomenology of Inert Scalar and Supersymmetric Dark Matter." Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-39278.
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While the dark matter has so far only revealed itself through the gravitational influence it exerts on its surroundings, there are good reasons to believe it is made up by WIMPs – a hypothetical class of heavy elementary particles not encompassed by the Standard Model of particle physics. The Inert Doublet Model constitutes a simple extension of the Standard Model Higgs sector. The model provides a new set of scalar particles, denoted inert scalars because of their lack of direct coupling to matter, of which the lightest is a WIMP dark matter candidate. Another popular Standard Model extension is that of supersymmetry. In the most minimal scenario the particle content is roughly doubled, and the lightest of the new supersymmetric particles, which typically is a neutralino, is a WIMP dark matter candidate. In this thesis the phenomenology of inert scalar and supersymmetric dark matter is studied. Relic density calculations are performed, and experimental signatures in indirect detection experiments and accelerator searches are derived. The Inert Doublet Model shows promising prospects for indirect detection of dark matter annihilations into monochromatic photons. It is also constrained by the old LEP II accelerator data. Some phenomenological differences between the Minimal Supersymmetric Standard Model and a slight extension, the Beyond the Minimal Supersymmetric Standard Model, can be found. Also, supersymmetric dark matter models can be detected already within the early LHC accelerator data.
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Nadathur, Seshadri. "Inflation, large-scale structure and inhomogeneous cosmologies." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:b8c5c6ff-53be-4c1e-97bc-4442c5bfba30.
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Determining cosmological parameters from current observational data requires knowledge of the primordial density perturbations generated during inflation. We begin by examining a model of inflation along a flat direction of the minimal supersymmetric Standard Model (MSSM) and the power spectrum of perturbations it can produce. We consider the fine-tuning issues associated with this model and discuss a modification of the potential to include a hybrid transition that reduces the fine-tuning, without affecting the viability of the model. However, supersymmetric flat directions might play a role in other models of inflation as well. In particular, they may cause a feature in the primordial power spectrum of perturbations, unlike the scale-free spectrum assumed in the standard Lambda Cold Dark Matter (LCDM) cosmological model. We then show that in the presence of such a feature, an alternative cosmological model with a large local void and no dark energy provides a good fit to both Type Ia supernovae and the cosmic microwave background (CMB) data from the WMAP satellite. Constraints from the locally measured Hubble parameter, baryon acoustic oscillations and primordial nucleosynthesis are also satisfied. This degeneracy motivates a search for other independent observational tests of LCDM. The integrated Sachs-Wolfe (ISW) imprint of large-scale structure on the CMB is one such test. The ISW imprint of superstructures of size ~100 Mpc/h at redshift z~0.5 has been detected with >4 sigma significance, however it has been noted that the signal is much larger than expected. We revisit the calculation using linear theory predictions in a LCDM cosmology and find the theoretical prediction is inconsistent by >3 sigma with the observation. If the observed signal is indeed due to the ISW effect then huge, extremely underdense voids are far more common in the observed universe than predicted by LCDM.
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Jendrysik, Christian [Verfasser], Siegfried [Akademischer Betreuer] Bethke, and Jonathan J. [Akademischer Betreuer] Finley. "Development and characterisation of silicon photomultipliers with bulk-integrated quench resistors for future applications in particle and astroparticle physics / Christian Jendrysik. Gutachter: Jonathan J. Finley ; Siegfried Bethke. Betreuer: Siegfried Bethke." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1054419868/34.
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Obranovich, Michael A. "The effects of non-zero neutrino masses on the CMB determination of the cosmological parameters." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337799009.
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Vertongen, Gilles. "The fall and rise of antimatter: probing leptogenesis and dark matter models." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210200.
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Big Bang Nucleosynthesis (BBN), together with the analyses of the Cosmic Microwave Background (CMB) anisotropies, confirm what our day to day experience of life attests :antimatter is far less present than matter in the Universe. In addition, these observables also permit to evaluate that there exists about one proton for every 10^{10} photons present in the Universe. This is in contradiction with expectations coming from the standard hot big bang, where no distinction between matter and antimatter is made, and where subsequent annihilations would lead to equal matter and antimatter contents, at a level 10^{−10} smaller than the observed one. The Standard Model of fundamental interactions fails to explain this result, leading us to search for ‘Beyond the Standard Model’ physics.Among the possible mechanism which could be responsible for the creation of such a matter asymmetry, leptogenesis is particularly attractive because it only relies on the same ingredients previously introduced to generate neutrino masses. Unfortunatelly, this elegant proposal suffers from a major difficulty :it resists to any tentative of being probed by our low energy observables. In this thesis, we tackle the problem the other way around and propose a way to falsify this mechanism. Considering the type-I leptogenesis mechanism, i.e. a mechanism based on the asymmetric decay of right-handed neutrinos, in a left-right symmetric framework, we show that the observation of a right-handed gauge boson W_R at future colliders would rule out any possibility for such mechanism to be responsible of the matter asymmetry present in our Universe.
Another intriguing question that analyses of the anisotropies of the CMB confirmed is the presence of a non-baryonic component of matter in our Universe, i.e. the dark matter. As hinted by observations of galactic rotation curves, it should copiously be present in our galactic halo, but is notoriously difficult to detect directly. We can take advantage on the fact that antimatter almost disappeared from our surroundings to detect the contamination of cosmic rays from standard sources the annihilation products of dark matter would produce.
The second subject tackled in this work is the study of the imprints the Inert Doublet Modem (IDM) could leave in (charged) cosmic rays, namely positrons, antprotons and antideuterons. This model, first proposed to allow the Bout-Englert-Higgs particle to evade the Electroweak Precision Test (EWPT) measurements, introduces an additional scalar doublet which is inert in the sense that it does not couple directly to fermions. This latter property brings an additional virtue to this additional doublet :since it interacts weakly with particles, it can play the role of dark matter. This study will be done in the light of the data recently released by the PAMELA, ATIC and Fermi-GLAST collaborations, which reported e^± excesses in two different energy ranges.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Carvalho, Fabio Cabral. "Teorias escalares-tensoriais e o regime superacelerado do universo: aspectos dinâmicos." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-14112013-141225/.
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Analisamos, em particular, a estabilidade das soluções tipo tracker. Nossa análise é global, baseando-se na existência de funções de Lyapunov para pontos críticos previamente identificados na literatura e já estudados no regime linear local. Aplicamos a metodologia desenvolvida no contexto cosmológico para encontrar soluções superaceleradas, definidas quando a equação de estado é muito negativa ( = p/ < -1), e estimar a bacia de atração em torno dos pontos fixos estáveis. Baseado nestes resultados, propomos um modelo livre de instabilidades clássicas e/ou quânticas capaz de descrever a recentemente descoberta fase de expansão acelerada do Universo, incluindo os eventuais regimes superacelerados levemente favorecidos pelos dados observacionais disponíveis atualmente.We analyzes, in particular, the stability of tracker solutions. Our analyzes is global, based in the existence of Lyapunov functions for fixed points previously identified in the literature and studied in the local linear regime. The methodology developed in the cosmological context is applied to find superaccelerated solutions, defined when the equation of state is very negative ( = p/ < -1), and to obtain the attraction basin around the stable fixed point. Based in these results, we propose a model free of classical and/or quantum instabilities, capable of describing the recently discovered fase of accelerated expantion of the Universe, including the possible superaccelerated regime slightly favored by the available observational data.
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Wallisch, Benjamin. "Cosmological probes of light relics." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283003.
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One of the primary targets of current and especially future cosmological observations are light thermal relics of the hot big bang. Within the Standard Model of particle physics, an important thermal relic are cosmic neutrinos, while many interesting extensions of the Standard Model predict new light particles which are even more weakly coupled to ordinary matter and therefore hard to detect in terrestrial experiments. On the other hand, these elusive particles may be produced efficiently in the early universe and their gravitational influence could be detectable in cosmological observables. In this thesis, we describe how measurements of the cosmic microwave background (CMB) and the large-scale structure (LSS) of the universe can shed new light on the properties of neutrinos and on the possible existence of other light relics. These cosmological observations are remarkably sensitive to the amount of radiation in the early universe, partly because free-streaming species such as neutrinos imprint a small phase shift in the baryon acoustic oscillations (BAO) which we study in detail in the CMB and LSS power spectra. Building on this analytic understanding, we provide further evidence for the cosmic neutrino background by independently confirming its free-streaming nature in different, currently available datasets. In particular, we propose and establish a new analysis of the BAO spectrum beyond its use as a standard ruler, resulting in the first measurement of this imprint of neutrinos in the clustering of galaxies. Future cosmological surveys, such as the next generation of CMB experiments (CMB-S4), have the potential to measure the energy density of relativistic species at the sub-percent level and will therefore be capable of probing physics beyond the Standard Model. We demonstrate how this improvement in sensitivity can indeed be achieved and present an observational target which would allow the detection of any extra light particle that has ever been in thermal equilibrium. Interestingly, even the absence of a detection would result in new insights by providing constraints on the couplings to the Standard Model. As an example, we show that existing bounds on additional scalar particles, such as axions, may be surpassed by orders of magnitude.
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Elmer, Martin. "Nouvelle physique entre cosmologie et le LHC : axions, neutrinos et Z'." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10178/document.
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Pendant mes trois ans de doctorat j'ai eu le plaisir de travailler sur trois projets très variés ayant un but commun: mieux contraindre certains modèles de nouvelle physique entre cosmolo- gie et le LHC. Le fait que les densités reliques de matière noire et de baryons sont similaires semble indiquer qu'il y a un lien entre les deux. Nous essayons d'expliquer les valeurs observées en reliant un modèle de leptogenèse au miracle des WIMPs, qui produit naturellement la bonne densité relique. Si l'asymétrie baryonique est produit dans des désintégrations hors équilibre à l'échelle électro-faible et si la matière noire est constituée de WIMPs, les deux densités reliques sont con- trôlées par des processus électro-faibles hors équilibre. Je construis un modèle de leptogenèse à l'échelle du TeV en utilisant une extension du type seesaw inverse du modèle standard avec des singlets additionnels. Pour produire suffisamment d'asymétrie baryonique il faut une violation CP ∼ O(1) qui est difficile à obtenir dans mon cadre. Les axions, tout comme les WIMPs sont de bons candidats de matière noire bien motivés. Il serait très utile de pouvoir les distinguer. Sikivie argumente que si des axions sont dans un condensat de Bose-Einstein, alors ils forment des halos galactiques différents des halos de WIMPs. D'après Sikivie ce sont les interactions gravitationnelles qui thermalisent les axions et qui les condensent. La formation d'un condensat nécessite la génération d'entropie qui ne peut pas être fourni par les interactions gravitationnelles au premier ordre. J'étudie la génération d'entropie par les interactions gravitationnelles en estimant une longueur de dissipation dans le fluide d'axions qui vient de la présence d'une pression anisotrope. Je ne peux pas confirmer la thermalisation rapide d'axions causé par leurs interactions gravitationnelles. Des nouveaux bosons de jauges comme le Z' apparaissent dans un grand nombre d'extensions du modèle standard. On les recherche le plus souvent comme une résonance dans le spectre de masse invariante de leurs produits de désintégration. Le Z' doit être produit sur couche de masse dans ces recherches résonantes. Mais la présence d'un Z' peut aussi influencer d'autres observ- ables cinématiques sans être produit directement, ce qu'on peut utiliser dans des recherches non-résonantes. Je compare ces deux types de recherches au LHC et trouve que pour des petits couplages les recherches résonantes sont plus adaptées mais pour de plus grandes masses et couplages les recherches non-résonantes sont plus performantesDuring the three years as a PhD student I had the pleasure to work on three major projects which are united in the goal to better constrain new physics models between cosmology and the LHC. The similar values of dark matter and baryon relic abundances raise the question whether there is a link between them. We attempt to explain the observed values by relating leptogenesis to the WIMP miracle which gives naturally the right relic abundance. If the baryon asymmetry is produced in electroweak-scale-out-of-equilibrium decays and dark matter is made of WIMPs, both relic densities are controlled by electroweak scale interactions going out of equilibrium. We construct a TeV-scale leptogenesis model using an inverse-seesaw extension of the SM with additional singlets. To produce a large enough asymmetry we require CP violation ∼ O(1) which is difficult to achieve in our set-up. Axions as well as WIMPs are well motivated dark matter candidates. It would be very useful to be able to tell them apart. Sikivie argues that if axions are in a Bose-Einstein condensate they could form a different galactic dark matter halo than WIMPs and that gravitational interactions drive axions into a Bose-Einstein condensate. However for the formation of such a condensate entropy generation is needed which leading order gravitational interactions do not provide. We explore the entropy generation of gravitational interactions by estimating a dissipation scale in the axion fluid due to the presence of a anisotropic stress. We cannot confirm a fast gravitational thermalisation rate. New neutral gauge bosons like the Z' are generic extensions of the standard model which appear in many different models. Traditionally these particles are searched for in resonant searches at colliders, i.e. by producing the particles on-shell and looking for a resonance in the invariant mass spectrum of their decay products. However the presence of a Z' can also affect other kinematic observables without being actually produced on-shell, i.e. non-resonant searches. We compare compare resonant and non-resonant searches at the LHC and find that while for small couplings resonant searches are more sensitive, for larger couplings non-resonant searches are more efficient
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Fradette, Anthony. "Particle physics probes from cosmology." Thesis, 2017. https://dspace.library.uvic.ca//handle/1828/8918.
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In this dissertation, we explore the cosmological sensitivity of well-motivated extensions of the Standard Model (SM) of particles. We focus on two specific models, the vector portal and the Higgs portal, that can connect the SM to a dark sector of new hidden particles. We find that both portals have sensitivity in the ultra-weak coupling regime, where the relic abundance is set by the freeze-in mechanism. Provided that the mediators of the portal interactions decay into the SM, we derive the constraints on masses and couplings of such states from precision cosmology. As a primary source of constraints, we use Big Bang Nucleosynthesis (BBN), the Cosmic Microwave Background (CMB) and the diffuse X-ray background. For the Higgs portal scalar, we improve the relic abundance calculation in the literature and provide an estimate of thermal corrections to the freeze-in yield. We find that the cosmological bounds are relatively insensitive to improvements in the abundance accuracy, and a full finite-temperature calculation is not needed.
We also investigate the BBN constraints for hypothetical long-lived metastable scalars particles $S$ that can be produced at the Large Hadron Collider from decays of the Higgs boson. We find that for viable branching ratios Br($h \to SS$), the early universe metastable abundance of $S$, regulated by its self-annihilation through the Higgs portal, is so large that the lifetime of $S$ is strongly constrained to $\tau_S < 0.1$~s to maintain the consistency of BBN predictions with observations. This provides a useful upper bound on the lifetimes of $S$ particles that a purposely-built detector, such as the one suggested in the MATHUSLA proposal, seek to discover.
We also investigate the viability and detectability of freeze-in self-interacting fermionic dark matter communicating with the SM via a vector portal. We focus on the parameter where the $\chi \bar{\chi} \to A'A'$ is negligible, as required by a variety of indirect detection constraints. We find that planned upgrades to the direct detection experiments will be able to probe the region of parameter space that can alleviate small scale structure problems of dark matter via self-interactions for a dark fine structure constant as small as $\alpha_d =10^{-4}$. We forecast the sensitivity for Lux-ZEPLIN, XENONnT and PandaX-4T.Graduate
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Guo, Huicheng. "Topics in particle physics and cosmology." 2009. http://wwwlib.umi.com/dissertations/fullcit/3362828.
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Salem, Michael Phillip. "Topics in theoretical particle physics and cosmology." Thesis, 2007. https://thesis.library.caltech.edu/1953/1/thesis.pdf.
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We first delve into particle phenomenology with a study of soft-collinear effective theory (SCET), an effective theory for Quantum Chromodynamics for when all particles are approximately on their light-cones. In particular, we study the matching of SCET(I) involving ultrasoft and collinear particles onto SCET(II) involving soft and collinear particles. We show that the modes in SCET(II) are sufficient to reproduce all of the infrared divergences of SCET(I), a result that was previously in contention.
Next we move into early universe cosmology and study alternative mechanisms for generating primordial density perturbations. We study the inhomogeneous reheating mechanism and extend it to describe the scenario where the freeze-out process for a heavy particle is modulated by sub-dominant fields that received fluctuations during inflation. This scenario results in perturbations that are comparable to those generated by the original inhomogeneous reheating scenarios. In addition, we study yet another alternative to single field inflation whereby the curvature perturbation is generated by interactions at the end of inflation, as opposed to when inflaton modes exit the horizon. We clarify the circumstances under which this process can dominate over the standard one and we show that it may result in a spectrum with an observable level of non-Gaussianities.
We then turn to studies of the landscape paradigm, which hypothesizes that the observed universe is just one among a multitude of possibilities that are realized in separate causal regions. Such a landscape has been used to explain the smallness of the cosmological constant, at least when only it scans across the landscape. We study the scenario where both the cosmological constant and the strength of gravity, parameterized by the effective Planck mass, scan across the landscape. We find that selection effects acting on the cosmological constant are significantly weaker in this scenario and we find the measured value of the Planck mass to be exponentially unlikely under certain plausible assumptions about the landscape. Finally, we study some other models of the landscape as part of a possible explanation for quark-sector flavor parameters in the Standard Model. In this picture quark Yukawa couplings result from overlap integrals involving quark and Higgs wavefunctions in compactified extra dimensions, and the values we measure result from random selection from a landscape of possibilities. We find that many of the salient features of the measured flavor parameters are typical of the landscape distribution.
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Underwood, Bret James. "Warped string phenomenology : topics in cosmology and particle Physics /." 2008. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Krislock, Abram Michael. "Making the Dark Matter Connection Between Particle Physics and Cosmology." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-08-9998.
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Dark matter has been shown to be extremely abundant in our universe. It comprises about 23 percent of the energy density of the entire universe, which is more than five times greater than the regular matter we already know about. Dark matter cannot be explained within the Standard Model of particle physics. However, models which extend the Standard Model, such as supersymmetry, can explain dark matter. This dissertation investigates the signals of some supersymmetry models in the context of collider physics. If dark matter particles or other supersymmetry particles are produced at some collider experiment, such as the Large Hadron Collider, it is important to know how we can find and measure the signatures and properties of these particles. This dissertation provides some measurement techniques for that exact purpose. These measurement techniques are also very general, making them useful for examining other models of particle physics as well. Lastly, if the supersymmetry model can be understood well enough from collider data, the connection back to cosmology can be made. Namely, it is possible to determine (from LHC data and using a standard cosmological calculation) the abundance of dark matter in the universe. Comparing this collider value with the value already measured will be a crucial step in understanding dark matter. This dissertation provides simulated results of this dark matter abundance calculation for a number of supersymmetry model points.
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Jenkins, Alejandro. "Topics in particle physics and cosmology beyond the standard model." Thesis, 2006. https://thesis.library.caltech.edu/2403/1/thesis.pdf.
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We review our understanding of spin-1 and spin-2 massless particles as mediators of long-range forces. We discuss how a quantum description of such particles that is compatible with Lorentz covariance leads to gauge invariance, a mathematical redundancy in the description of the physics. We discuss the Weinberg-Witten theorem, which underlines the need for gauge invariance in relativistic theories with massless mediators of higher spin.
This leads us to consider a class of models in which long-range interactions are mediated by the Goldstone bosons of spontaneous Lorentz violation. Since the Lorentz symmetry is realized non-linearly in the Goldstones, these models could evade the Weinberg-Witten theorem and the need for gauge invariance. In the case of gravity, the broken symmetry would protect the theory from having non-zero cosmological constant, while the compositeness of the graviton could provide a solution to the perturbative non-renormalizability of gravity.
Next we consider the phenomenology of spontaneous Lorentz violation and the experimental limits thereon. We find the general low-energy effective action of the Goldstones of this kind of symmetry breaking minimally coupled to gravity. We compare this effective theory to the ghost condensate that has been proposed in the literature as a model for gravity in a Higgs phase. We compute the modification to Newton's law from this mechanism and discuss observational limits on this kind of Lorentz violation from solar system tests of gravity and from gravitational Cherenkov radiation of cosmic rays.
We then summarize the cosmological constant problems and show that models in which a scalar field causes super-acceleration of the universe generally exhibit instabilities connected to violation of the null-energy condition. We discuss how the equation of state evolves in a universe where the dark energy is caused by a ghost condensate. We comment on the anthropic argument for a small cosmological constant and how it is weakened if the inflaton self-coupling varies over the landscape of possible universes.
Finally, we discuss the reverse sprinkler, a problem in elementary fluid mechanics that had eluded a definitive treatment for decades.