Dissertations / Theses: 'Astrophysics and Cosmology'

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Whiting, Alan B. "Local cosmology." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360010.

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Wong, D. "Cosmology and superstrings." Thesis, University of Sussex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381634.

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Webster, R. L. "Gravitational lensing and cosmology." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355284.

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Nilsson, Ulf. "Dynamical systems in cosmology and astrophysics /Ulf Nilsson." Stockholm : Stockholms Universitet, 1998. http://www.gbv.de/dms/goettingen/254604390.pdf.

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Keränen, Petteri. "Aspects of massive neutrinos in astrophysics and cosmology." Helsinki : University of Helsinki, 1999. http://ethesis.helsinki.fi/julkaisut/mat/fysii/vk/keranen/.

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Powell, Andrew James. "The cosmology and astrophysics of axion-like particles." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:bbbb3cbc-a0ba-4024-86b0-c720d8104270.

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In this thesis I study astrophysical and cosmological effects of axion-like particles (ALPs). ALPs are pseudo-scalar particles, which are generally very weakly-interacting, with a coupling α/M E · B to electromagnetism. They are predicted by many theories which extend the standard model (SM) of particle physics, most notably string theory. String theory compactifications also predict many scalar fields called moduli which describe the size and shape of the extra, compact dimensions. In string theory models generically the moduli fields are responsible for reheating the universe after inflation. Being gravitationally-coupled, they will also decay to any other particles or sectors of the theory, including any light ALPs, of which there are usually many. The ALPs produced by moduli decay will contribute to dark radiation, additional relativistic energy density. The amount of dark radiation is tightly constrained by observations, this bounds the branching fraction of moduli decays into ALPs, which constrains the string theory model itself. I calculate the amount of dark radiation produced in a model with one light modulus, solely responsible for reheating, called the Large Volume Scenario. I study a minimal version of this model with one ALP and a visible sector comprised of the minimal supersymmetric SM. The dominant visible sector decay mode is to two Higgses, I include radiative corrections to this decay and find that ALP dark radiation is over-produced in this minimal version of the model, effectively ruling it out. The production of ALPs from moduli decay at reheating seems to be a generic feature of string theory models. These ALPs would exist today as a homogeneous cosmic ALP background (CAB). The coupling of ALPs to electromagnetism allows ALPs to convert to photons and vice versa in a magnetic field, leading to potential observable astrophysical signals of this CAB. Observations have shown an excess in soft X-ray emission from many galaxy clusters. I use detailed simulations of galaxy cluster magnetic fields to show that a CAB can explain these observations by conversion of ALPs into X-ray photons. I simulate ALP-photon conversion in four galaxy clusters and compare to soft X-ray observations. I show the excesses (or lack thereof) can be fit consistently across the clusters for a CAB with ALP-photon inverse coupling of M = 6 - 12 x 10¹² GeV, if the CAB spectrum has energy ~ 200 eV. I also study the possibility of using galaxy clusters to search for and constrain the ALP coupling to photons using cluster X-ray emission. Conversion of X-ray photons into ALPs will cause spectral distortions to the thermal X-ray spectrum emitted by galaxy clusters. I show that the non-observation of these distortions is able to produce the strongest constraints to date on the ALP-photon inverse coupling, M ≳ 7 x 10¹¹ GeV.

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Mellor, Felicity Avril. "Black holes and quantum cosmology." Thesis, University of Newcastle Upon Tyne, 1990. http://hdl.handle.net/10443/682.

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The work of this thesis falls into two parts: a discussion of decoherence in quantum Kaluza-Klein theories and a study of some of the properties of general black hole metrics in de Sitter spacetime. Kaluza-Klein theories permit a variety of compactifications and arbitrary scales for the internal space. There must be no quantum interference between these different possibilities. In chapter one it is demonstrated that in the Salam-Sezgin compactification interference between differently scaled interenal spaces is suppressed. In chapter two new gravitational instantons are presented which are related to charged, rotating black holes with a cosmological constant A. These instantons correspond to black holes in de Sitter space with identical Hawking temperatures. Their action contributes terms of order A-1/2 to path integrals with quantum wormholes. The metrics of these general de Sitter black holes show that the spacetimes have wormholes connecting different asymptotic regions. In chapter three the theory of black hole perturbations is extended to these metrics. It appears that the holes are stable even at the Cauchy horizon. This implies that cosmic censorship is violated. The stability of the spacetimes also implies the existence of a cosmological no hair theorem.

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Stevenson, Paul Robert Frederick. "Faint galaxy photometry and cosmology." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/6800/.

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Deep galaxy catalogues have been constructed from automatic measurements of photographic plates by the COSMOS machine at the Royal Observatory Edinburgh. The plates were taken by the 1.2m UK Schmidt telescope (UKST) and 4m Anglo-Australian telescope (AAT), in both blue and red passbands. The UKST plates cover an area of sky of~170 square degrees, some four times larger than any previous study to these depths (B-21, R~20mag).By comparing the UKST and AAT galaxy number-magnitude counts and colour distributions with those predicted using computer models, evidence for luminosity evolution has been obtained. The red passband counts require less luminosity evolution than in the blue passband and at the faintest magnitudes reached here (R'-22mag) the cosmological parameter, q(_o), has as large an effect. The red count models are well enough determined to reject world models with q(_o)> 1. In order to further separate the effects of luminosity evolution and q^, the possibility of using a well determined Hubble diagram or faint "galaxy redshift surveys is considered. The galaxy two-point angular correlation function, w(ɵ), has been estimated from the UKST catalogues and shows evidence of a feature at large angular scales, corresponding to a spatial separation of ~3h Mpc (H(_o) = l00h kms Mpc ). In a study of the correlation function scaling relation it is found that the observed clustering amplitudes at AAT depths are lower than those predicted using well determined models that assume no clustering evolution. However, sampling errors are large and more 4m data is required in order to test the reality of this result. Also discussed is the possibility of discriminating between recent theories of galaxy formation using the w(#) observations. The method of Turner and Gott has been used to automatically detect groups and clusters of galaxies in the UKST catalogues. It is found that the cluster-cluster w(f) is several times higher than the galaxy-galaxy w(4) when scaled to the same depth. The implications of this result for galaxy formation theories are discussed. By using the average magnitude, m, of a cluster as a distance estimator the redshift distribution of the clusters has been obtained. Features present in these distributions^ may correspond to the effects of superclustering on scales < l50h (^-1)Mpc. The modelled m:distance relation has been used to set constraints on the galaxy luminosity function and hence help to more tightly constrain the number count and clustering models. The orientations of galaxies within clusters and the orientations and ellipticity distributions of the clusters themselves have been used in order to obtain further constraints on the theories of galaxy formation.

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Skea, T. "Anisotropic cosmology and curvature invariants." Thesis, University of Sussex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381633.

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Borrill, Julian. "The cosmology of global texture." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335012.

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Betschart, Gerold. "General relativistic electrodynamics with applications in cosmology and astrophysics." Doctoral thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/4948.

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Durrive, Jean-Baptiste. "Baryonic processes in the large scale structuring of the Universe." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS346/document.

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Ma thèse porte sur deux questions importantes de la Cosmologie:(i) L'origine des champs magnétiques cosmologiques:L'Univers semble magnétisé à absolument toutes ses échelles (spatiales et temporelles), y compris le milieu intergalactique. Mais leur origine est encore inconnue à l'heure actuelle, malgré les nombreux efforts pour essayer de répondre à cette question. On pense qu'ils ont d'abord été générés avec de très faibles amplitudes, puis qu'ils ont été amplifiés au cours de la formation des structures. La turbulence dans les galaxies et les amas de galaxies modifie totalement l'organisation initiale de ces champs, ce qui fait que les champs observés actuellement dans les structures ne nous renseignent pas sur leur origine. Il convient donc de s'intéresser aux champs intergalactiques. J'ai dévelopé analytiquement un modèle de magnétogénèse basé sur la photoionisation du milieu intergalactique par les premières étoiles et les premières galaxies apparues dans l'Univers, il y a environ 13 milliards d'années. Puis, en collaboration avec H. Tashiro et N. Sugiyama (Japon), j'ai calculé de façon analytique la densité d'énergie moyenne injectée par ce processus dans le contexte cosmologique, et en parallèle, en collaboration avec D.Aubert (France), j'ai étudié les propriétés statistiques du champs généré à travers des simulations numériques. Nos prédictions sont compatibles avec les observations actuelles. Ce mécanisme a donc dû participer à la magnétisation de l'Univers à ses plus grandes échelles.(ii) Fragmentation gravitationnelle de la toile cosmique:Les simulations numériques suggèrent que la matière dans l'Univers est répartie de façon filamentaire, les noeuds de ce réseau étant les amas de galaxies. La matière s'écoule le long de ces filaments. L'accrétion dans les noeuds est donc anisotrope, et il s'avère qu'elle est aussi en partie intermittente. Cela indique que la matière ne se structure pas uniquement dans les amas, mais aussi dans les filaments, voire les nappes ou les vides cosmiques. Je me suis donc intéressé à l'instabilité gravitationnelle dans les milieux stratifiés. J'ai proposé une nouvelle approche, dans le cadre de la théorie spectrale, en m'inspirant de la littérature plasma
My thesis deals with two important topics of Cosmology:(i) Origin of cosmological magnetic fields:Magnetic fields seem ubiquitous in the Universe, present at all scales and all times, probably even in the entire intergalactic medium. Their origin is still unclear, especially on the largest scales. The current paradigm is that they were first generated with extremely weak strengths, and later amplified during structure formation. Because of turbulence, the fields we observe in galaxies and galaxy clusters lost their initial characteristics. However, in less dense regions such as cosmological filaments, sheets or voids, magnetic fields have evolved more mildly. Therefore, intergalactic magnetic fields may still possess a memory of the processes that generated them and hold the key to their origin. I developed analytically a detailed physical model of a natural astrophysical mechanism that generates intergalactic magnetic fields during the first billion year, namely at the time when first stars and galaxies were born. Then, in collaboration with H. Tashiro and N. Sugiyama (Japan), I computed analytically the mean energy density injected in the entire Universe through this mechanism. Independently, in collaboration with D. Aubert (France), I derived the topological and statistical properties of the magnetic field thus generated, using cosmological numerical simulations. This way I demonstrated that this simple, natural photoionization-based magnetogenesis must have created magnetic seed fields with properties a priori perfectly compatible with present day observations.(ii) Gravitational fragmentation of the cosmic web:Cosmological numerical simulations suggest that the Universe has a web-like structure, the nodes of which are galaxy clusters. These nodes are supplied with matter flowing along the filaments interconnecting them. Part of this accretion occurs intermittently, which indicates that clumps of matter form not only inside clusters themselves, but also either in cosmic voids, walls and/or filaments. I studied gravitational instability in stratified media in the frame of spectral theory, in planar and cylindrical geometries, relevant for cosmic walls and filaments, for isothermal, polytropic, and with and without an external gravitational background (e.g. Dark Matter). I have recasted the problem as an eigenvalue problem in the force operator formalism, and derived the wave equation governing the growth of perturbations. I also studied it in matrix form, which gives complementary information

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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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Ahmed, Maqbool. "First indications of causal set cosmology." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2006. http://proquest.umi.com/login?COPT=REJTPTU0NWQmSU5UPTAmVkVSPTI=&clientId=3739.

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Gruber, Christine [Verfasser]. "Quantum Phenomena in the Realm of Cosmology and Astrophysics / Christine Gruber." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1045859265/34.

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Broadhurst, Thomas James. "A faint galaxy redshift survey and implications for cosmology." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6536/.

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A new faint galaxy redshift survey has been constructed using the fibre optic coupler at the Anglo-Australian Observatory. Intermediate dispersion spectra with resolution ~ 4 A have been gathered for over 200 field galaxies selected in apparent magnitude slices between 20.0 < b(_j) < 21.5 in 5 high latitude fields. Redshift completeness is 85% and the mean redshift agrees well from field to field Models for the prediction of faint galaxy distributions are constructed from a bright galaxy redshift survey (Durham/Anglo-Australian Redshift Survey) and show that although the slope of the galaxy number-magnitude count relation is considerably steeper than no-evolution predictions at b(_j) ~ 21, the redshift range observed is similar to that expected for a non-evolving population. If our fields are representative, luminosity evolution can only be occurring in low luminosity galaxies to (_z) < 0.5.The faint spectra reveal strong evidence for enhanced star formation in a large proportion of the galaxies beyond z ~ 0.1 which cannot be explained in terms of colour or aperture selection-effects. We suggest that it is these star-forming galaxies which represent the excess in the galaxy counts, at least in the range b(_j) < 22.The colour and absorption line features of the stronger emission fine galaxies can only be reproduced with models incorporating strong short-lived bursts of star formation which temporarily brighten these otherwise low-luminosity systems. We are able to reproduce these observations with a physical 'burst' model in which only galaxies at the faint end of the luminosity function significantly evolve via short (lO(^8)yrs) bursts of star formation. These results are supported by model comparison with very faint colour distributions. We find good agreement with the no-evolution model in the range b(_j) – R(_j) > 1.6, indicating a minimum of evolution of bright early type galaxies. The excess number count is clearly concentrated blueward of this, and consistent with the expectation of the burst model. Clustering on small scales, estimated via the 2-point spatial correlation function agrees fairly well with local results, but evidence for a very large scale periodicity may be indicated by combining this survey with others in the direction of the Galactic poles.

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Okouma, Patrice M. "Type Ia supernovae as tools for cosmology." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4424.

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Mertens, James B. "Application of Methods from Numerical Relativity to Late-Universe Cosmology." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1484497200032472.

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Macaulay, Edward Robert Mark. "Cosmology with power spectrum measurements from galaxy surveys." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bb918260-6747-4133-bdcb-b393d080c6fa.

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The nature of dark matter and dark energy are currently two of the most important questions in cosmology. In this thesis, we consider studying the dark universe with the redshifts and peculiar velocities of galaxies. In the first half of the thesis, we analyse current peculiar velocity measurements of the bulk flow of our local volume to estimate the underlying dark matter power spectrum. In the second half of the thesis, we consider the prospects for measuring dark matter and dark energy with future galaxy redshift surveys, particularly via redshift space distortions. Fundamentally, bulk flow measurements and redshift space distortions are both sensitive probes of the power spectrum and growth rate of cosmic structure. In the final chapter, we directly compare power spectrum measurements with both methods.

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Johansson, Jonas. "The chemical evolution of unresolved stellar populations : from stellar astrophysics to cosmology." Thesis, University of Portsmouth, 2011. https://researchportal.port.ac.uk/portal/en/theses/the-chemical-evolution-of-unresolved-stellar-populations(0a98af92-add8-4740-b2f9-5ac26c63b695).html.

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Stars light up galaxies that are the major building blocks of the Universe. Throughout this thesis we cover the analysis of stars and stellar populations to gain knowledge on the formation of galaxies and the evolution of the Universe. Understanding massive earlytype galaxies is key to understand mass assembly and the formation and evolution of galaxies in the Universe. The spectra of stellar populations carry a wealth of information regarding galaxy formation and evolution. Absorption lines are particularly useful as they are tracers of galaxy formation epoch and time-scale. Models of stellar populations are important tools for the analysis of galaxies. The accuracy of such models are crucial for the accuracy of the derived results. The first step in my thesis is therefore to improve upon current single stellar population models of absorption line indices. Calibration of the models with galactic globular cluster is crucial, since these are known to be close to single stellar populations. The main aim of the thesis is to apply the models to the analysis of earlytype galaxies and Type Ia supernovae (SN Ia) host galaxies. The main novelty of the stellar population models are new empirical calibrations of absorption line indices. These are based on the most comprehensive stellar library available to date MILES. The stellar spectra of this library have been carefully flux-calibrated. The models are therefore applicable to data without Lick index calibrations. Based on the new stellar population models we have developed a method for deriving element abundance ratios, including [O/Fe], [C/Fe], [N/Fe], [Mg/Fe], [Ca/Fe] and [Ti/Fe]. The method is applied to galactic globular clusters and we find the models to be well calibrated. The pattern of derived element abundance ratios show strong evidence for self-enrichment within globular clusters. The method for deriving element abundance ratios is then applied to �4000 SDSS early-type galaxies. The element abundance ratios [O/Fe], [Mg/Fe], [C/Fe] and [N/Fe] show strong correlations with stellar velocity dispersion. Using the derived trends of element abundance ratios we constrain the lower time-scale limit of star formation and star-burst components in massive early-type galaxies to �0.4 Gyr. Both in the globular cluster and early-type galaxy study we find that the heavy �-elements Ca and Ti scale with Fe rather than with the lighter �-elements O and Mg. This implies that a significant contribution from SN Ia to the enrichment of heavy �-elements is universally found and puts strong constraints on supernova nucleosynthesis and models of galactic chemical evolution. SN Ia as standard candles connect luminosity distance to redshift space to constrain cosmology. We derive stellar population parameters for a quality selected sample of 84 SN Ia host galaxies. We find that the stretch factor of SN Ia light-curves are mainly dependent on stellar population age, indicating that SN Ia progenitor mass is the main driver of the peak luminosities. We do not find any significant dependencies on host galaxy properties for the scatter in the luminosity-distance relationship after light-curve corrections. This implies that the derived cosmological parameters from SN Ia peak luminosities are robust.

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Vogel, Hendrik [Verfasser], and Georg [Akademischer Betreuer] Raffelt. "Density matrix equations in astrophysics and cosmology / Hendrik Vogel. Betreuer: Georg Raffelt." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1110749279/34.

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Stewart, Ewan Davidson. "Axion cosmology : the behaviour of the Peccei-Quinn field during inflation." Thesis, Lancaster University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332083.

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Tie, Suk Sien. "Lyman-alpha forest cosmology with the Dark Energy Spectroscopic Instrument (DESI)." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1594035656891479.

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Papastergis, Emmanouil. "Statistical analysis of ALFALFA galaxies| Insights in galaxy formation & near-field cosmology." Thesis, Cornell University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3574823.

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The Arecibo Legacy Fast ALFA (ALFALFA) survey is a blind, extragalactic survey in the 21cm emission line of atomic hydrogen (HI). Presently, sources have been cataloged over ≈4,000 deg² of sky (~60% of its final area), resulting in the largest HI-selected sample to date. We use the rich ALFALFA dataset to measure the statistical properties of HI-bearing galaxies, such as their mass distribution and clustering characteristics. These statistical distributions are determined by the properties of darkmatter on galactic scales, and by the complex baryonic processes through which galaxies form over cosmic time. As a result, detailed studies of these distributions can lead to important insights in galaxy formation & evolution and near-field cosmology.

In particular, we measure the space density of HI-bearing galaxies as a function of the width of their HI profile (i.e. the velocity width function of galaxies), and find substantial disagreement with the distribution expected in a lambda cold dark matter (ΛCDM) universe. In particular, the number of galaxies with maximum rotational velocities υ_rot ≈ 35 kms^–1 (as judged by their HI velocity width) is about an order of magnitude lower than what predicted based on populating ΛCDM halos with modeled galaxies. We identify two possible solutions to the discrepancy: First, an alternative dark matter scenario in which the formation of low-mass halos is heavily suppressed (e.g. a warm dark matter universe with keV-scale dark matter particles). Secondly, we consider the possibility that rotational velocitites of dwarf galaxies derived from HI velocity widths may systematically underestimate the true mass of the host halo, due to the shape of their rotation curves. In this latter scenario, quantitative predictions for the internal kinematics of dwarf galaxies can be made, which can be checked in the future to probe the nature of dark matter.

Furthermore, we take advantage of the overlap of ALFALFA with the Sloan Digital Sky Survey (SDSS), to measure the number density of galaxies as a function of their “baryonic” mass (stars + atomic gas). In the context of a ΛCDM cosmological model, the measured distribution reveals that low-mass halos are heavily “baryon depleted”, i.e. their baryonic-to-dark mass ratio is much lower than the cosmological value. These baryon deficits are usually attributed to stellar feedback (e.g. supernova-driven gas outflows), but the efficiency implied by our measurement is extremely high. Whether such efficient feedback can be accommodated in a consistent picture of galaxy formation is an open question, and remains one of the principle scientific drivers for hydrodynamic simulations of galaxy formation.

Lastly, we measure the clustering properties of HI-selected samples, through the two-point correlation function of ALFALFA galaxies. We find no compelling evidence for a dependence of clustering on HI mass, suggesting that the relationship between galactic gas mass and host halo mass is not tight. We furthermore find that HI galaxies cluster more weakly than optically selected ones, when no color selection is applied. However, SDSS galaxies with blue colors have very similar clustering characteristics with ALFALFA galaxies, both in real as well as in redshift space. On the other hand, HI galaxies cluster much more weakly than optical galaxies with red colors, and in fact “avoid” being located within ≈3 Mpc from the latter. By considering the clustering properties of ΛCDM halos, we confirm our previous intuition for an M_HI-M_h relation with large scatter, and find that spin parameter may be a key halo property related to the gas content of present-day galaxies.

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Visbal, Elijah Francis. "Future Probes of Cosmology and the High-Redshift Universe." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10823.

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This thesis is a study in theoretical cosmology with an emphasis on the high-redshift universe and promising directions for future observations. In Chapters 2 and 3, we propose intensity mapping of spectral line emission from galaxies. This is a technique to observe the cumulative emission from many galaxies without resolving individual sources. We use analytic calculations and N-body simulations to predict the observational signal for different emission lines, including those from oxygen, carbon monoxide, and carbon.
Physics

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Soergel, Bjoern. "The kinematic and thermal Sunyaev-Zel'dovich effects as probes of cosmology and astrophysics." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277657.

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A small fraction of cosmic microwave background (CMB) photons scatter off electrons in the ionised gas in collapsed structures. This process, known as the Sunyaev-Zel'dovich effect, is usually broken down into a thermal (tSZ) and a kinematic (kSZ) contribution. While the former is sensitive to the random velocities of the electrons in the hot gas, the latter is sourced by the bulk motion of the entire object. In this thesis I measure the signature of both of these effects by cross-correlating CMB data with different tracers of the large-scale structure. I further study how these effects can be used as probes of cosmology and astrophysics. I first report a statistically significant detection of the kSZ effect. This is achieved by combining a cluster catalogue derived from the first year data of the Dark Energy Survey with CMB temperature maps from the South Pole Telescope. I perform the measurement with a differential statistic that isolates the pairwise kSZ signal, providing the first detection of the large-scale motion of clusters using redshifts derived from photometric data. By fitting the pairwise kSZ signal to a theoretical template, I measure the average central optical depth of the cluster sample. I compare the extracted signal to simulations and find good agreement with respect to the signal-to-noise, the constraint on the optical depth, and the corresponding gas fraction. I next study the potential of the kSZ effect as a probe of cosmology, again focussing on the pairwise method. The main challenge is disentangling the cosmologically interesting mean pairwise velocity from the cluster optical depth and the associated uncertainties on the baryonic physics in clusters. Using the Magneticum cosmological hydrodynamical simulations I calibrate a scaling relation between the amplitude of the tSZ signal and the optical depth. I show that this relation can be used to recover an accurate estimate of the mean pairwise velocity from the kSZ signal, and that this effect can therefore be used as a probe of cosmology. I finally derive constraints on feedback from active galactic nuclei by setting limits on their tSZ signal. By combining all-sky microwave, sub-mm, and far-infrared data from the Planck and AKARI satellites, I break the degeneracy between the tSZ signature and extragalactic dust emission. I test the measurement pipeline with a catalogue of galaxy clusters, finding the expected high-significance tSZ detection together with correlated dust emission. I then measure the tSZ signal of spectroscopically confirmed quasi-stellar objects (QSOs), but obtain only a low-significance hint of a tSZ signature. This analysis leads to a lower mean thermal energy than reported in some previous studies which were contaminated by dust emission. A comparison of these results to hydrodynamical simulations can be used as a probe of QSO host masses.

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Gangler, Emmanuel. "The nearby SuperNova Factory : des CCD a la cosmologie." Habilitation à diriger des recherches, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00854994.

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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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Tinker, Jeremy L. "Constraining cosmology with the Halo occupation distribution." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1120663291.

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Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xviii, 319 p.; also includes graphics. Includes bibliographical references (p. 310-319). Available online via OhioLINK's ETD Center

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Dutta, Sourish. "TOPICS IN COSMOLOGY: ISLAND UNIVERSES, COSMOLOGICAL PERTURBATIONS AND DARK ENERGY." online version, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1183797241.

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Murphy, Kellen J. "Constraining Cosmology with Weak Gravitational Lensing." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1384957353.

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Mazzanti, Liuba. "Systèmes intégrables non commutatifs et la correspondance Ads/CFT en cosmologie." Phd thesis, Ecole Polytechnique X, 2007. http://pastel.archives-ouvertes.fr/pastel-00003164.

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Ma these se deroule suivant deux principales lignes de recherche. Les deux arguments traites constituent une relation entre la theorie des cordes et les aspects phenomenologiques/cosmologiques. D'une part, la geometrie noncommutative (NC) est une consequence naturelle de la presence de branes et ﬂux dans la theorie des cordes. La non commutativite deforme certaines proprietes fondamentales des theories ordinaires decrivant par exemple les interactions electro–faibles et fortes ou les modeles statistiques. C'est dans ce sens que la geometrie NC represente une application a la phenomenologie des cordes. D'autre part, les branes sont l'ingredient clé des modeles d'univers branaires. Le modele de Randall–Sundrum (RS) en particulier oﬀre de nouvelles perspectives tant du point de vue de la cosmologie, ouvrant des scenarios d'evolution cosmologique non conventionnelle, que du point de vue de l'holographie. La premiere partie de la these est dediee a la geometrie NC et, en particulier, aux theories de champs NC integrables. Le but principal du travail a ete d'etudier les consequences de la non commutativit´e par rapport a l'integrabilite. Plus precisement, on a voulu veriﬁer ou refuter dans un contexte NC le theoreme qui lie, en deux dimensions, l'integrabilite a la factorisation de la matrice S. Avec integrabilite on parle de l'existence d'un nombre inﬁni de courants locaux conserves, associes aux symetries de la theorie de champs.Le point de depart a donc ete de garantir la presence de tels courants, au moyen du formalisme du bicomplexe. Cette methode permet d'obtenir les equations du mouvement en tant que conditions d'int´ egrabilite d'un systeme d'equations diﬀerentielles lineaires. a partir des solutions du meme systeme lineaire suivent les courants conserves. En exploitant le formalisme de Weyl, la procedure est immediatement generalisable a la geometrie NC. Une algebre de fonctions (operateurs de Weyl) deﬁnie sur un espace NC est associee a une algebre NC de fonctions ou la multiplication est executee au moyen d'un produit NC de Moyal: le produit. En introduisant le produit au niveau du systeme lineaire et en en deduisant les equations du mouvement NC, on obtient la generalisation NC du bicomplexe. On a infere le premier modele en generalisant le bicomplexe du modeledesine–Gordon(SG)a la geometrie NC. Nous avons deduit (en collaboration avec Grisaru, Penati, Tamassia) l'action correspondante aux equations du mouvement precedemment etablies par Grisaru et Penati. Le calcul des amplitudes de diﬀusion et production a determine les caracteristiques de la matrice S du modele. Des comportements acausaux ont ete releves pour les processus de diﬀusion. En outre, les processus de production possedent une amplitudes non nulle: d'ou la non validite du theoreme d'integrabilite vs. factorisation pour cette version NC du modele de SG. D'autres proprietes ont ete mises en evidence, comme la relation avec la theorie des cordes et la bosonisation. Le deuxieme modele de SG NC a ete propose en collaboration avec Lechtenfeld, Penati, Popov, Tamassia. Les equations du mouvement ont ete tirees de la reduction dimensionnelle du modele sigma NC en 2+1 dimensions, qui a son tour est la reduction de la theorie de self–dual Yang–Mills NC en 2+2 dimensions (decrivant les supercordes N =2avecchamps B). L'action a ete calculee de meme que les amplitudes. Les processus de production possedant des amplitudes nulles et ceux de diﬀusion ne dependant pas du parametre de NC, entraınent ainsi un comportement causal. Le deuxieme modele de SG NC semble donc obeir a l'equivalence entre integrabilite et factorisation de la matrice S. La reduction de la theorie des cordes garde sa validite meme au niveau de l'action contrairement au modele precedent. La deuxieme partie de ma these traite des modeles d'univers branaires, ou plus precisement des modeles de RS. Le modele propose par Randall et Sundrumse situe dans un bulk 5–dimensionnel, caracterise per une symetrie d'orbifold Z2 par rapport `a la position de la brane 4–dimensionnelle. Grace au facteur de warp qui multiplie le sous–espace 4–dimensionnel parallele a la brane, on obtient la localisation des modes du graviton. Par consequent, le potentiel gravitationnel eﬃcace est newtonien aux energies inferieures a la masse de Planck. En introduisant en outre un terme de matiere dans le bulk et en considerant l'echange d'energie entre brane et bulk, une variete de nouvelles cosmologies en derive. Dans la premiere partie de mon travail sur RS nous avons propose un modele analogue situe dans un bulk 7–dimensionnel. La brane 6–dimensionnelle — ayant compactiﬁe deux dimensions — est placee au point ﬁxe de l'orbifold Z2. Aﬁn d'etudier l'evolution cosmologique en nous mettant en relation avec les observations, nous avons introduit l'echange d'energie entre brane et bulk. Les scenarios possibles sont nombreux et dependent de la forme explicite du parametre d'echange d'energie. Entre autres, les points ﬁxes possedent une acceleration positive, pouvant ainsi representer la recente acceleration de l'univers. Il sont egalement stables pour un large ensemble des valeurs des parametres. Finalement, on peut tracer des scenarios qui partent d'une phase initiale acceleree, en passant successivement a une ere de deceleration, pour terminer sur un point ﬁxe stable d'inﬂation. Les modeles d'univers branaires a la RS possedent un dual holographique via AdS/CFT. La correspondance AdS/CFT etablit qu'une theorie de supergravite(ou,plusg´ en´ eralement, de cordes) dans un champ de fond d'anti de Sitter (AdS) en d + 1 dimensions est duale a une theorie de champs conforme (CFT) en d dimensions. Tenant compte des divergences presentes dans les deux descriptions, cette correspondance a ete rendue plus precise par la formulation de la renormalisation holographique. Si l'espace de AdS est regularise au moyen d'un cutoﬀ infrarouge, la correspondante CFT resulte regularisee par un cutoﬀ ultraviolet et couplee a la gravite d–dimensionnelle. En analogie a l'analyse eﬀectuee en cinq dimensions par Kiritsis, nous avons construit la theorie duale au modele cosmologique de RS en sept dimensions. Pour capturer les dynamiques dictees par l'echange d'energie entre brane et bulk, la theorie holographique en six dimensions a ete generalisee au cas interagissant (entre matiere et CFT) et non conforme. Le resultat sont les relations entre les parametres de masse appartenant aux deux descriptions et entre l'echange d'energie, d'un cote, et le parametre d'interaction, de l'autre. De plus, le parametre de rupture conforme est associe au parametre d'auto–interaction du bulk dans la description de supergravite 7–dimensionnelle. Le travail de recherche inclut donc des resultats pouvant trouver leur application dans la phenomenologie et cosmologie des cordes. D'une part on a enqueter sur l'inﬂuence de la noncommutativite liee a l'integrabilite du modele de SG. D'autre part, les consequences cosmologiques de l'emplacement du modele de RS en sept dimensions ont ete etudiees et la correspondance AdS/CFT a ete appliquee aﬁn d'en tirer des informations sur la theorie duale, couplee a la gravite.

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Walker, Emma Suzanne. "Quantatitive analysis of type Ia supernova spectra and implications for cosmology." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:680bf64e-0d23-4570-ad18-e19f74f4b950.

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This thesis presents the spectroscopic observations of the Supernova Legacy Survey (SNLS) from the Gemini-North telescope from May 2006 – May 2008. During this time 68 of 95 targets were confirmed as Type Ia supernovae (SNe Ia) or classified as probable SNe Ia events. We use these objects and reanalyse other high-z spectra obtained as part of SNLS to search for signs of evolution in SNe Ia properties. To do this we use a multicolour method to remove host galaxy contamination from the high-z spectra and measure the equivalent widths of three spectral features in the rest-frame blue part of the spectrum: CaII H&K, SiII and Mg II. These are compared to a sample of low-z objects drawn from the literature. No evidence for evolution is found, but a change in the properties of the SiII feature is observed. This can be explained by changing supernova demographics, an outcome of the two-component progenitor model for SNe Ia. The utility of SNe Ia supernovae for cosmology is confirmed and the possible use of spectral features as alternative calibrators is investigated. The equivalenth width of the SiII feature is anticorrelated with light curve stretch and this is used to define a "spectral stretch" from the low-z sample, which is used to reduce the scatter in the low-z sample. This holds promise for improving the calibration of high-z SNe Ia, particularly if new facilities are used to provide higher-quality spectra.

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34

Prunet, Simon. "Polarisation du ciel micro-ondes." Phd thesis, Université Paris Sud - Paris XI, 1998. http://tel.archives-ouvertes.fr/tel-00008317.

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La mission ESA Planck offre une opportunité sans précédent de mesurer de manière très précise la polarisation de l'émission Galactique et extragalactique dans le domaine millimétrique et sub-milli\-métrique ; elle devrait notamment permettre de mesurer la polarisation du Fond Cosmique Micro-ondes (FCM). Dans le premier chapitre, nous expliquons brièvement l'intérêt scientifique d'une telle mesure, et revoyons les technologies instrumentales qui la permettent. Dans le second chapitre, nous modélisons les caractéristiques statistiques de l'émission galactique polarisée, en particulier celle des poussières (plus particulièrement importante pour l'instrument haute fréquence -HFI- de Planck). Dans le troisième chapitre, nous présentons une méthode de filtrage multi-fréquence permettant la séparation des différentes composantes astrophysiques de l'émission millimétrique et sub-millimétrique, et permettant de quantifier les erreurs de la mesure des propriétés statistiques (spectre de puissance) de ces différents processus, en particulier le FCM. Dans le quatrième chapitre, nous estimons l'erreur commise sur la mesure des paramètres cosmologiques, conséquence des erreurs estimées au chapitre précédent. Dans un cinquième chapitre, nous estimons la contribution aux anisotropies du FCM de l'effet de lentille gravitationnelle en mouvement, causé par une population d'amas et de groupes de galaxies. Enfin, dans un sixième chapitre, nous présentons un modèle semi-analytique simple de formation de galaxies, où le taux de formation d'étoiles est controlé par la température du milieu intergalactique.

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張礎恆 and Chor-hang Paul Cheung. "Solutions of wormhole in the generalized Brans-Dicke theory." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31215075.

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Cheung, Chor-hang Paul. "Solutions of wormhole in the generalized Brans-Dicke theory /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19737968.

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Godley, Andrew R. "A search for [nu mu to nu e] oscillations in the NOMAD experiment." Connect to full text, 2000. http://hdl.handle.net/2123/374.

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Thesis (Ph. D.)--University of Sydney, 2001.
Squiggly right arrow used in title. Title from title screen (viewed Apr. 23, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Degree awarded 2001; thesis submitted 2000. Includes bibliography. Also available in print form.

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Zu, Ying. "Cross-Correlation Cluster Cosmology." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376958777.

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Lee, Sujeong. "Tools for Cosmology - Combining Data from Photometric and Spectroscopic Surveys." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1565788614586566.

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40

Juramy, Claire. "Métrologie des supernovae de type Ia pour la cosmologie : instrumentation et analyse calorimétrique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2006. http://tel.archives-ouvertes.fr/tel-00592266.

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L'utilisation des supernovae de type Ia comme indicateurs de distance est un pilier du modèle de concordance actuel en cosmologie. Le travail d'instrumentation présenté dans la première partie a été réalisé dans le cadre d'un projet utilisant ces objets, le satellite SNAP, qui nécessite la spatialisation d'un grand plan focal comportant des détecteurs CCD pour le visible et APS pour l'infra-rouge. Pour tester la lecture de ces détecteurs à très bas bruit, nous avons construit deux bancs de test cryogéniques et étudié en détail un ASIC analogique. La deuxième partie est l'analyse de données existantes dans le cadre de notre modèle "calorimétrique", pour améliorer l'utilisation des SN Ia comme étalons. Le programme GRATIS calcule le dépot d'énergie radioactive dans la supernova. La comparaison avec les puissances lumineuses mesurées est satisfaisante. D'autres pistes incluent l'évolution des spectres en phase tardive et l'observation d'un saut de couleur baptisé "rayon vert".

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Van, De Rijt Nicolas. "Signatures de l'univers primordial dans les grands relevés cosmologiques." Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00727811.

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L'étude des grandes structures de l'Univers est un des meilleurs moyens pour comprendre l'origine et l'évolution de l'Univers. Dans cette thèse, nous nous spécialisons aussi bien dans la théorie des perturbations aux échelles cosmologiques, que dans le cisaillement cosmique. La théorie des perturbations aux échelles cosmologiques décrit comment les grandes structures de l'Univers se sont formées à partir des minuscules fluctuations primordiales. Cette évolution est généralement décrite en se servant des équations du mouvement d'un fluide, et dans cette thèse nous introduisons quelques nouvelles versions de cette hiérarchie de Boltzmann. Les avantages et inconvénients de ces nouvelles hiérarchies sont analysés en détail. Nous introduisons aussi une nouvelle technique, appelée l'approximation eikonal, qui nous permet de mieux comprendre les résultats des autres approches utilisées en théorie des perturbations. En outre, grâce à sa généralité, elle nous permet de généraliser une grande quantité de résultats. Le cisaillement cosmique décrit comment l'effet des lentilles gravitationnelles déforme notre image du ciel. Dans cette thèse, nous étudions de manière détaillée le bispectre du cisaillement cosmique, au deuxième ordre en les potentiels gravitationnels. Le calcul est intégralement fait en "full sky", généralisant ainsi les résultats existants. Pour simplifier les calculs numériques, nous introduisons et généralisons l'approximation dite de Limber.

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Sakstein, Jeremy Aaron. "Astrophysical tests of modified gravity." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/246265.

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Einstein's theory of general relativity has been the accepted theory of gravity for nearly a century but how well have we really tested it? The laws of gravity have been probed in our solar system to extremely high precision using several different tests and general relativity has passed each one with flying colours. Despite this, there are still some mysteries it cannot account for, one of which being the recently discovered acceleration of the universe and this has prompted a theoretical study of modified theories of gravity that can self-accelerate on large scales. Indeed, the next decade will be an exciting era where several satellites will probe the structure of gravity on cosmological scales and put these theoretical predictions to the test. Despite this, one must still worry about the behaviour of gravity on smaller scales and the vast majority of these theories are rendered cosmologically uninteresting when confronted with solar system tests of gravity. This has motivated the study of theories that differ from general relativity on large scales but include screening mechanisms which act to hide any modifications in our own solar system. This then presents the problem of being able to distinguish these theories from general relativity. In the last few years, astrophysical scales have emerged as a new and novel way of probing these theories. These scales encompass the mildly non-linear regime between galactic and cosmological scales where the astrophysical objects have not yet joined the Hubble flow. For this reason, the screening mechanism is active but not overly efficient and novel effects may be present. Furthermore, these tests do not require a large sample of galaxies and hence do not require dedicated surveys; instead they can piggyback on other experiments. This thesis explores a class of theories of screened modified gravity which are scalar-tensor theories where the field is conformally coupled to matter via the metric and includes chameleon and symmetron models as well as those that screen using the environment-dependent Damour-Polyakov effect. The thesis is split into two parts. The first is aimed at searching for new and novel astrophysical probes and using them to place new constraints on the model parameters. In particular, we derive the equations governing hydrodynamics in the presence of an external gravitational field that includes the modifications of general relativity. Using this, we derive the equations governing the equilibrium structure of stars and show that unscreened stars are brighter and hotter than their screened counterparts owing to the larger nuclear burning rate in the core needed to combat the additional inward force. These theories have the property that the laws of gravity are different in unscreened galaxies from our own. This means that the inferred distance to an unscreened galaxy using a stellar effect that depends on the law gravity will not agree with a measurement using a different method that is insensitive gravitational physics. We exploit this property by comparing the distances inferred using pulsating Cepheid variable stars, tip of the red giant branch stars and water masers to place new constraints on the model parameters that are three orders of magnitude stronger than those previously reported. Finally, we perturb the equations of modified gravity hydrodynamics to first order and derive the equations governing the oscillations of stars about their equilibrium structure. By solving these equations we show that unscreened stars are more stable to small perturbations than screened stars. Furthermore, we find that the oscillation period is far shorter than was previously estimated and this means that the current constraints can potentially be improved using previous data-sets. We discuss these new results in light of current and future astrophysical tests of modified gravity. The final part of this thesis is dedicated to the search for supersymmetric completions of modified theories of gravity. There have been recent investigations into the quantum stability of these models and there is evidence that they may suffer from quantum instabilities. Supersymmetric theories enjoy powerful non-renormalisation theories that may help to avoid these issues. For this reason, we construct a framework for embedding these models into global supersymmetry and investigate the new features this introduces. We show how supersymmetry is broken at a scale set by the ambient density and that, with the exception of no-scale models, supergravity corrections already constrain the model parameters to levels where it is not possible to probe the theories with astrophysics or laboratory experiments. Next, we construct a class of supersymmetric chameleon models and investigate their cosmology. In particular, we find that they are indistinguishable from the LCDM model at the background level but that they may show deviations in the cold dark matter power spectrum that can be probed using upcoming experiments. Finally, we introduce a novel mechanism where a cosmological constant in the form of a Fayet-Illiopoulos term can appear at late times and investigate the constraints this imposes on the model parameter space.

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Zheng, Zheng. "Constraining galaxy bias and cosmology using galaxy clustering data." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092257217.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xix, 302 p. : ill. (some col.). Advisor: David H. Weinberg, Department of Astronomy. Includes bibliographical references (p. 291-302).

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Bird, Jonathan C. "The Formation and Evolution of Disk Galaxies." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1345571232.

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45

Westmoreland, Shawn. "Energy conditions and scalar field cosmology." Kansas State University, 2013. http://hdl.handle.net/2097/15811.

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Master of Science
Department of Physics
Bharat Ratra
In this report, we discuss the four standard energy conditions of General Relativity (null, weak, dominant, and strong) and investigate their cosmological consequences. We note that these energy conditions can be compatible with cosmic acceleration provided that a repulsive cosmological constant exists and the acceleration stays within certain bounds. Scalar fields and dark energy, and their relationships to the energy conditions, are also discussed. Special attention is paid to the 1988 Ratra-Peebles scalar field model, which is notable in that it provides a physical self-consistent framework for the phenomenology of dark energy. Appendix B, which is part of joint-research with Anatoly Pavlov, Khaled Saaidi, and Bharat Ratra, reports on the existence of the Ratra-Peebles scalar field tracker solution in a curvature-dominated universe, and discusses the problem of investigating the evolution of long-wavelength inhomogeneities in this solution while taking into account the gravitational back-reaction (in the linear perturbative approximation).

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Nguyen, Nhat-Minh [Verfasser], and Eiichiro [Akademischer Betreuer] Komatsu. "Bayesian forward modeling of galaxy clustering : cosmology and astrophysics inference / Nhat-Minh Nguyen ; Betreuer: Eiichiro Komatsu." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1213246334/34.

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47

Amblard, Alexandre. "Analyse des anisotropies du fond diffus cosmologique dans le cadre de l'expérience ARCHEOPS." Phd thesis, Université Paris Sud - Paris XI, 2002. http://tel.archives-ouvertes.fr/tel-00001684.

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Ma thèse porte sur l'étude des anisotropies du fond diffus cosmologique dans le cadre de l'expérience Archeops. Archeops est une expérience dédiée à la mesure de ces anisotropies sur une large région d'échelle angulaire et embarquée sous un ballon stratosphérique. Cette expérience est préliminaire à la mission satellite Planck. Après avoir décrit le mode de formation des anistropies du fond diffus cosmologique et les connaissances sur notre Univers que l'on peut extraire de leurs propriétés, je décris l'expérience Archeops : ses instruments, ses capacités, ses objectifs scientifiques. Mon travail au sein de la collaboration Archeops est centré sur la soustraction des effets synchrones avec la rotation de la nacelle pour obtenir un étalonnage des détecteurs sur le dipôle cosmologique et sur la reconstruction du spectre de puissance. Tout d'abord je passe en revue les différentes sources de signaux synchrones avec la rotation de la nacelle en me concentrant sur l'émission atmosphérique, puis décris les méthodes que j'ai développées pour soustraire ces contributions. Deux de ces méthodes sont ensuite appliquées sur les données et permettent d'obtenir un étalonnage des détecteurs. La seconde partie de ma thèse montre comment on peut reconstruire le spectre de puissance des anisotropies. La validité du calcul du spectre de puissance est ensuite testée sur les données. Pour extraire le spectre de puissance des anisotropies à partir du signal je présente une métode que j'ai développée pour évaluer la contribution du bruit au spectre, et une autre pour supprimer la contamination galactique. En conclusion la chaîne de calcul est testée complètement sur des simulations qui reproduisent les propriétés des données de manière très précise.

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Langer, Mathieu. "Origine du champ magnétique en cosmologie et formation des galaxies." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2002. http://tel.archives-ouvertes.fr/tel-00002495.

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Ma thèse est le fruit d'un travail théorique centré sur deux questions fondamentales de la cosmologie actuelle: la formation des galaxies d'une part, et l'origine des champs magnétiques à grande échelle d'autre part. Je propose une solution au problème du sur-refroidissement dont souffrent les modèles de formation des galaxies. Pour cela, à l'aide d'un modèle analytique simple, puis au moyen de simulations numériques, j'explore les mécanismes de transfert et de stockage d'énergie par ondes d'Alfvén en œuvre dans le milieu interstellaire (MIS) biphasique. Je montre d'une part que les interférences des ondes internes aux nuages du MIS, négligées dans les études précédentes, renforcent l'efficacité d'injection d'énergie. D'autre part, les mouvements des nuages redistribuent l'énergie à l'échelle du système entier. Ils injectent aussi de l'énergie dans les nuages. Les modes vibratoires internes excités s'opposent à la compression des nuages et prolongent la durée de vie du système. Les nuages magnétisés constituent alors un réservoir d'énergie sur plusieurs temps dynamiques. A l'aide d'un modèle de protogalaxie biphasique, je montre que la dynamique des nuages du MIS et celle d'une protogalaxie sont équivalentes. Pour résoudre le sur-refroidissement, je propose la transposition des résultats du MIS au cas protogalactique. Malgré les diverses tentatives passées, l'origine du champ magnétique en cosmologie n'a pas trouvé d'explication satisfaisante. Or, sa place au sein du MIS et son rôle dans la formation des galaxies sont manifestes. Je propose dans ma thèse un nouveau mécanisme de magnétogenèse efficace à grande échelle, opérant à la réionisation de l'Univers, et reposant sur la pression de radiation anisotrope et inhomogène fournie par les premières structures lumineuses. A l'échelle galactique, le champ magnétique que j'obtiens est huit ordres de grandeur plus intense que dans les modèles habituels. De plus, il est généré avant tout aux grandes échelles, les champs à petite échelle étant largement supprimés. Ces deux propriétés permettent au modèle proposé de rendre compte des champs observés dans les grandes structures.

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Ng, Shao-Chin Cindy. "Cosmological models with quintessence : dynamical properties and observational constraints." Title page, table of contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phn5758.pdf.

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Bibliography: leaves 100-106. Studies different models of "quintessence", in particular, a quintessence arising from an ultra-light pseudo Nambu-Goldstone boson. Overviews dynamical properties for these models using phase-space analyses to study attractor and tracker solutions. Studies high-redshift type Ia supernovae constraints on these models. Studies the impact of a simple phenomenological model for supernovae luminosity evolution on the PNGB models and the potentials of a future supernovae data set to discriminate the PNGB models over the other quintessence models. Studies gravitational lensing statistics of high luminosity quasars upon the quintessence models.

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50

Sousbie, Thierry. "LE SQUELETTE DE L'UNIVERS: Un outil d'analyse topologique des grandes structures." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2006. http://tel.archives-ouvertes.fr/tel-00162559.

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La distribution de la matière dans l'Univers est supposée homogène et isotrope à très grande échelle mais l'observation de la distribution des galaxies lors
de grandes campagnes de recensements comme le SDSS nous montre un véritable réseau d'amas et de filaments sur des échelles de plusieurs centaines de
mégaparsecs.\\

De nombreuses méthodes ont été développées dans le but de caractériser cette distribution et nous nous proposons dans cette thèse de présenter l'adaptation en trois dimensions d'un nouvel outil: le squelette.
Cette méthode vise à donner une définition mathématique claire des filaments ainsi qu'un algorithme numérique robuste permettant leur identification ainsi que le calcul de leurs propriétés. \\

Afin de pouvoir comparer les résultats obtenus à partir des simulations N-corps de matière noire aux observations, une nouvelle méthode, baptisée MoLUSC, spécialisée dans la création de catalogues virtuels de
galaxies a aussi été élaborée. Elle se base sur les modèles semi-analytiques et est particulièrement efficace pour la fabrication de catalogues de grande
taille simulant de manière suffisamment réaliste les propriétés galactiques.\\

Les utilisations de ces deux outils sont nombreuses et nous montrons par exemple qu'il est possible en mesurant la densité de longueur des filaments à
une échelle donnée de contraindre la quantité de matière dans l'univers
$\Omega_m$. Ces méthodes peuvent aussi être appliquées avec succès à la mesure statistique des propriétés du flux de matière noire le long des filaments, une mesure inédite. Nous présentons enfin de nombreuses applications possibles dont les résultats préliminaires sont très encourageants.

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Dissertations / Theses on the topic 'Astrophysics and Cosmology'

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