In this thesis, we investigate the signatures of isocurvature initial conditions in the cosmic microwave background (CMB) through the temperature and polarization anisotropies, and in the large-scale structure distribution through the baryon acoustic oscillations (BAO). The first part of this thesis is a brief review of the standard cosmological model with its underlying linear cosmological perturbation theory. We supplement it with a general discussion on the initial conditions of the primordial fluctuations. In the third chapter, we review the evolution of the perturbations in the adiabatic model. We focus on the evolution of adiabatic perturbations in the photons and baryons from the epoch of initial conditions to the photon-baryon decoupling, as these determine the main features of the primary CMB anisotropies and of the baryon acoustic oscillations. The fourth chapter recalls the theory of the CMB anisotropies in the adiabatic model. We consider the perturbations from the last scattering surface and evolve them through the line of sight integral to get the adiabatic CMB power spectrum. We review the effect of different cosmological parameters on the adiabatic CMB temperature spectrum. In the fifth chapter, we investigate the observational signatures of the isocurvature perturbations in the CMB anisotropies. We first derive simple semi-analytic expressions for the evolution of the photon and baryon perturbations prior to decoupling for the four isocurvature regular modes and show that these modes excite different harmonics which couple differently to Silk damping and alter the form and evolution of acoustic waves. We study the impact of different cosmological parameters on the CMB angular power spectrum through the line of sight integral and find that the impact of the physical baryon and matter densities in isocurvature models differ the most from their effect in adiabatic models. In the last two chapters, we explore in detail the effect of allowing for small amplitude admixtures of general isocurvature perturbations in addition to the dominant adiabatic mode, and their effect on the baryon acoustic oscillations. The sixth chapter focuses on the distortion of the standard ruler distance and the degradation of dark energy constants due to the inclusion of isocurvature perturbations, while the seventh chapter discusses in more detail the sensitivity of BAO dark energy constraints to general isocurvature perturbations. We stress the role played by Silk damping on the BAO peak features in breaking the degeneracy in the peak location for the different isocurvature modes and show how more general initial conditions impact our interpretation of cosmological data in dark energy studies. We find that the inclusion of these additional isocurvature modes leads to a significant increase in the Dark Energy Task Force figure of merit when considered in conjunction with CMB data. We also show that the incorrect assumption of adiabaticity has the potential to substantially bias our estimates of the dark energy parameters. We find that the use of the large scale structure data in conjunction with CMB data significantly improves our ability to measure the contributions of different modes to the initial conditions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [115]-119).

Physics measurements at the LHC rely on the imulation of the proton-proton interaction to estimate detector performance and physics ackgrounds. Therefore, a good understanding of ll the processes involved is crucial to the final precision of any measurement. Monte Carlo event generators try to provide a realistic description of the proton-proton collision by combining the theoretical models describing different stages of the interaction process. Within this framework, the baryon number transport and the hadronisation mechanism are currently described by phenomenological models that need input from experimental data. This thesis investigates these subjects in the unique kinematic region covered by the LHCb detector. The production cross section ratios of identified hadrons (protons, kaons and pions) have been measured as a function of pseudorapidity and transverse momentum both at $sqrt{s} = 0.9$ TeV and $sqrt{s} = 7$ TeV collisions using 320 $mub^{-1}$ and 1.8 $nb^{-1}$ of data respectively. The measurements are then compared to the predictions from several tunings of the PYTHIA Monte Carlo generator. In general, current models do not give a satisfactory description of the hadronisation and tend to underestimate the transport of the baryon number into the final state. Critical to this analysis is the particle identification provided by the LHCb Ring Imaging Cherenkov (RICH) system. To ensure high performance, a proper calibration of the RICH photon detectors response is necessary. A system for the calibration of the magnetic distortion induced by the LHCb dipole magnet onto the photon detectors is described. The system currently provides calibration parameters used in the LHCb event reconstruction software and introduces a critical improvement to the overall particle identification performance.

This thesis presents work carried out using data from the LHCb experiment during the first three years of data taking, 2010 - 2012. A study of the effects of radiation damage on the silicon sensors of the LHCb Vertex Locator is performed, with an emphasis on the implications for the long term performance of the detector. Following three years of operation the sensors have received a maximum delivered neutron equivalent fluence of approximately 1.6E12 per square centimeter, leading to a number of radiation induced effects. In particular the change in charge collection efficiency and signal/noise with fluence is compared to theoretical expectations, and the current trends are extrapolated to the fluences expected at the end of the LHCb detector lifetime. The development of an unexpected effect due to the structure of the routing lines in the sensors is described in detail. Searches for lepton flavour and baryon number violating decays of the tau lepton using the 2011 LHCb dataset are described. Observation of any lepton flavour or baryon number violation would be an unambiguous sign of new physics, whilst setting improved limits helps to constrain a number of Beyond the Standard Model theories. First LHCb limits are set on the branching fractions of the decays tau- to mu- mu+ mu-, tau- to anti-proton mu+ mu- and tau- to proton mu- mu-, with these results also representing the first limits on lepton flavour violating tau decays at a hadron collider. The limit on tau- to mu- mu+ mu- is expected to approach the world's best result from Belle in the coming years whilst the tau- to anti-proton mu+ mu- and tau- to proton mu- mu- results constitute the first limits on the branching fractions of these decays. The future prospects for these measurements with further data are briefly described.

権利表示を行うこと, 出典表示を行うこと, 出版社版へのリンクを表示すること / 京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19488号 / 理博第4148号 / 新制||理||1596(附属図書館) / 32524 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 大西 明, 准教授 菅沼 秀夫, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM