Cosmology is one of the best tools to understand the physics that governs the universe at high energies. On one hand, inflation is a very robust mechanism to explain the initial conditions of the universe. On the other hand general relativity provides a solid framework for the formation of cosmic structures at cosmological scales. Nevertheless, there are still important issues that remain without a clear answer. For example, inflation still lacks of a concrete microphysical description, and also there is still no satisfactory mechanism to explain the late time acceleration of the universe. This thesis addresses these two topics. In the first part we discuss the effects of heavy degrees of freedom coupled to inflation. This has been an important topic over the years, because the experimental success might make it possible to detect new degrees of freedom in inflation. In chapter two we discuss the case when non relativistic heavy fields are coupled to the inflaton through a non minimal gravitational coupling. Here we find that, for certain geometries, the heavy field can modify the potential for a few e-folds, either stopping inflation, or setting its initial conditions. In chapter 3 we study the dynamics of fluctuations in holographic inspired models of multi-field inflation. We find that the entropy mass $\mu$ (the mass of the fluctuation orthogonal to the trajectory of inflation) satisfies an universal upper bound given by $\mu \leq 3 H / 2$. This bound coincides with the requirement of unitarity of conformal operators living on the boundary of the theory. In the second part of the thesis we study high energy effects on the Cosmic Microwave Background (CMB). In the fourth chapter we study the role of disformal transformation on cosmological backgrounds and its relation to the speed of sound for tensor modes. A speed different from one for tensor modes can arise in several contexts such as Galileons theories, or massive gravity. Nevertheless the speed is very constrained to be one by observations of gravitational wave emission. It has been shown that in inflation a disformal transformation allows the speed for tensor modes, to be set to one without making changes to the curvature power spectrum. We show that on the CMB, after doing the transformation, there is an imprint on the acoustic peaks, and the diffusion damping. This has interesting consequences: for a particular class of theories the transformation can be used to constrain the parameter space in different regimes. In chapter five we study the impact of gravitons with non-vanishing masses on the polarisation of th CMB . We also focus on putative modifications to the speed of the gravitational waves. We find that a change of the graviton speed shifts the acoustic peaks of the B-mode polarization and then could be easily constrained. In all cases when both massless and massive gravitons are present, we find that the B-mode CMB spectrum is characterised by a low $l$ plateau together with a shifted position for the first few peaks compared to a massless graviton spectrum. This shift depends on the mixing between the gravitons in their coupling to matter and could serve as a hint in favour of the existence of multiple gravitons.

Um Detector de Ondas Gravitacionais tipo Massa-Ressonante Esférico é otimizado. Primeiramente um modelo matemático para o detector com seis transdulatores indutivos supercondutivos de dois modos é usado para simular o desempenho de tal detector. Depois disso, um conjunto completo de experimentos para melhorar os fatores de qualidade mecânico e elétrico do transdutor e dos acoplamentos entre suas partes é mostrado e os resultados, discutidos. / A Spherical Resonant-Mass Detector of Gravitational Waves is optimized. First, a mathematical model for the detector with six inductive superconducting two-mode transducers is used to simulate the performance of such detector. After that, a complete set of experiments to improve the mechanical and the electrical quality factors of the materials and the transducer attachments is shown, and the results are discussed.

No description available.

Weak gravitational lensing is now well established as a powerful cosmological probe, particularly for studying large scale structure growth in the Universe. The vast majority of weak lensing experiments to date use optical and near infrared observations which are well suited to the requirements in source densities and shape analysis. In this thesis we outline the prospects associated with weak lensing surveys from radio observations. This can offer key advantages to optical counterpart studies such as the well defined observing beam pattern of a radio telescope and a window into a much broader observed redshift distribution. In addition to the prospect of radio weak lensing surveys alone, combining with optical counterparts in a cross-correlation study has been shown to mitigate uncorrelated systematics, further motivating the case for radio based weak lensing studies. The correlation of galaxy shapes through multi-wavelength observations will affect the noise on the cosmological power spectrum in cross-correlation analysis. We use radio and optical observations of the COSMOS field with the VLA and HST respectively, accompanied with simulations for calibration in order to measure shape correlations between wavelength regimes. Although we do not detect a correlation between optical and radio shapes, a lower limit on the intrinsic astrophysical scatter was placed at >0.212pi (or 38.2 degrees), through a Monte Carlo simulation of source catalogues with the measured uncertainties. The SuperCLASS experiment aims to measure a weak lensing signal with radio observations from a super-cluster field. We introduce the radio data, collected with the e-MERLIN and JVLA, and the reduction steps taken. Assisted by simulations, we have designed a shape measurement pipeline (SuperTRAP) which performs additional phase rotation and averaging steps to extract visibility sets on a source by source basis followed by image plane shape analysis. A series of staged tests of increasing complexity are outlined here and evaluated by the shape recovery bias and efficiency. Finally we present the optical counterpart observations and shape analysis for the SuperCLASS field, with data collected by the Subaru Suprime-Cam. Observational systematics are measured to form representative PSF models in each CCD exposure and the subsequent shape analysis from the I band photometry is presented. Shear analysis from the measured power spectrum shows good agreement with theoretical predictions. From the measured shear power spectrum we detect a strong signal in the E-mode band powers, equivalent to a 9.31sigma detection. Our measurements from the B-mode and E-B cross band powers suggest negligible contamination from systematics. The optical analysis presented here will provide the counterpart analysis to the radio for future cross-correlation studies.

The Standard Model of cosmology successfully describes the observable Universe requiring only a small number of free parameters. The model has been validated by a wide range of observable probes such as Supernovae IA, the CMB, Baryonic Acoustic Oscillations and galaxy clusters. Weak Gravitational Lensing (WL) is becoming a popular observational technique to constrain parameters in the Standard Model and is particularly appealing to the scientific community because the tracers it relies on, image distortions, are unbiased probes of density fluctuations in the fabric of the cosmos. The WL effect is sensitive to the late time evolution of the Universe, in which structures are non--linear. Because of this, WL observations cannot be treated as Gaussian random fields and statistical information on cosmology leaks from quadratic correlations into more complicated, higher order, image features. The goal of this dissertation is to analyze the efficiency of some of these higher order features in constraining Standard Model parameters. We approach the investigation from a practical point of view, examining the analytical, computational and numerical accuracy issues that are involved in carrying a complete analysis from observational data to parameter constraints using these higher order statistics. This work is organized as follows: - In Chapter 1 we review the fundamentals of the LambdaCDM Standard Model of cosmology, focusing particularly on the Friedmann picture and on the physics of large scale density fluctuations. - In Chapter 2 we give an outline of the Gravitational Lensing effect in the context of cosmology, and we introduce the basic WL observables from an analytical point of view. - In Chapter 3 we review the relevant numerical techniques used in the modeling of WL observables, focusing in particular on the algorithms used in ray--tracing simulations. These simulations constitute the base of our modeling efforts. - In Chapter 4 we discuss feature extraction techniques from WL observations: we treat both quadratic statistics, such as the angular shear--shear power spectrum, and higher order statistics for which analytical treatment is not possible. - In Chapter 5 we review the Bayesian formalism behind the inference of LambdaCDM parameters from image features. We place particular emphasis on physical and numerical effects that degrade parameter constraints and discuss possible mitigations. -In Chapter 6 we apply the previously described techniques to the Canada France Hawaii LenS galaxy survey, showing how the use of higher order image statistics can improve inferences on the LambdaCDM parameters that describe density fluctuations. - In Chapter 7 we discuss some of the issues that arise in the analysis of a large scale WL survey such as the Large Scale Synoptic Survey: we focus on systematic effects caused by sensors imperfections, the atmosphere, redshift errors and approximate theoretical modeling. - In Chapter 8 we draw our conclusions and discuss possible future developments.

Lau, Hoi Kwan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 208-212). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Gravitational wave astronomy --- p.1 / Chapter 1.2 --- Stellar pulsation and gravitational radiation --- p.3 / Chapter 1.3 --- Outline --- p.5 / Chapter 2 --- Hydrostatic stellar structure --- p.8 / Chapter 2.1 --- Structural equation --- p.9 / Chapter 3 --- Finite temperature equations of state of nuclear matter --- p.13 / Chapter 3.1 --- Finite temperature ordinary nuclear matter --- p.13 / Chapter 3.2 --- Strange Quark Matter --- p.15 / Chapter 3.3 --- Equilibrium and Dynamic EOS --- p.16 / Chapter 4 --- Stellar pulsation and gravitational radiation --- p.19 / Chapter 4.1 --- Linearized theory of general relativity --- p.19 / Chapter 4.2 --- Stellar oscillation --- p.25 / Chapter 4.3 --- Quasi-normal Mode --- p.28 / Chapter 4.3.1 --- f mode --- p.29 / Chapter 4.3.2 --- p mode --- p.29 / Chapter 4.3.3 --- g mode --- p.30 / Chapter 4.3.4 --- w mode --- p.31 / Chapter 5 --- Gravitational wave spectrum of hot compact stars --- p.32 / Chapter 5.1 --- Numerical results --- p.32 / Chapter 5.1.1 --- Temperature effect on QNM --- p.32 / Chapter 5.1.2 --- Temperature effect and QS model --- p.38 / Chapter 5.1.3 --- QNM shift due to phase transition --- p.41 / Chapter 5.2 --- Summary and prospective --- p.48 / Chapter 6 --- Universality of fundamental mode and spacetime mode --- p.50 / Chapter 6.1 --- Review --- p.50 / Chapter 6.2 --- Generic proposal of universalities --- p.53 / Chapter 6.2.1 --- Moment of Inertia --- p.54 / Chapter 6.2.2 --- Gravitational wave spectrum --- p.57 / Chapter 6.3 --- Universality on moment of inertia --- p.63 / Chapter 6.4 --- Origin of universality --- p.70 / Chapter 6.4.1 --- Tolman VII model --- p.71 / Chapter 6.4.2 --- Polytropic Model --- p.76 / Chapter 6.5 --- Application of universality --- p.82 / Chapter 6.6 --- Summary --- p.89 / Chapter 7 --- Quark star properties and gravity mode oscillation --- p.92 / Chapter 7.1 --- Introduction --- p.92 / Chapter 7.2 --- g mode frequencies of quark stars --- p.94 / Chapter 7.2.1 --- Temperature profile and p mode frequency --- p.96 / Chapter 7.2.2 --- Strange quark mass and Yp mode frequency --- p.104 / Chapter 7.3 --- Summary --- p.108 / Chapter 8 --- Gravitational radiation excitation by infalling shell --- p.111 / Chapter 8.1 --- Introduction --- p.111 / Chapter 8.2 --- Formalism --- p.116 / Chapter 8.2.1 --- Connection between star and vacuum --- p.117 / Chapter 8.2.2 --- Matter source --- p.121 / Chapter 8.2.3 --- Geodesic --- p.124 / Chapter 8.2.4 --- Source of infalling dust shell --- p.126 / Chapter 8.2.5 --- Green's function --- p.127 / Chapter 8.3 --- Gravitational Wave excitation by collapsing shell --- p.130 / Chapter 8.4 --- Features of radiation --- p.138 / Chapter 8.4.1 --- Power spectrum --- p.138 / Chapter 8.4.2 --- Wave function --- p.144 / Chapter 8.4.3 --- Energy of excitation --- p.147 / Chapter 8.5 --- Non-adiabatic oscillation --- p.153 / Chapter 8.5.1 --- Mathematical Background --- p.154 / Chapter 8.5.2 --- Numerical results --- p.158 / Chapter 8.6 --- General relativistic simulation --- p.163 / Chapter 8.6.1 --- Technical briefing --- p.163 / Chapter 8.6.2 --- Numerical results --- p.166 / Chapter 8.7 --- Summary --- p.174 / Chapter 9 --- Conclusion and remarks --- p.178 / Chapter A --- Unit conversions --- p.183 / Chapter B --- Series expansion of quark star EOS --- p.185 / Chapter C --- Accuracy of simplified mode extraction scheme --- p.188 / Chapter D --- Computation of moment of inertia --- p.193 / Chapter E --- Comment of exactness of inference scheme --- p.195 / Chapter E.1 --- Precision of the mass inferred --- p.195 / Chapter E.2 --- Accuracy of universality combinations --- p.199 / Chapter F --- Calculation of sound speed --- p.202 / Chapter G --- Mode extraction of non-adiabatic oscillation --- p.204 / Bibliography --- p.208

Observations of gravitationally microlensed quasars offer a unique opportunity to probe quasar structure on extremely small scales. In this thesis, we conduct extensive microlensing simulations and compare with observational data to constrain quasar accretion discs, and conduct preliminary probes of broad emission line region structure. This analysis is done using a new single-epoch imaging technique that requires very little telescope time, and yet produces results that are comparable to those obtained from long-term monitoring campaigns. / We begin by exploring the impact of variable smooth matter percentage and source size on microlensing simulations. Adding a smooth matter component affects minimum and saddle point images differently, broadening the magnification distribution for the saddle point image significantly. However, increasing the radius of the background source washes out this difference. The observation of suppressed saddle point images can therefore only be explained by microlensing with a smooth matter component if the background source is sufficiently small. We use these simulations, in combination with I-band imaging of the lensed quasar MG 0414+0534 to constrain the radius of the quasar source. This demonstrates the viability of a single-epoch imaging method for constraining quasar structure. / This technique is then expanded to single-epoch multi-band observations, in order to constrain the radial profile of quasar accretion discs as a function of observed wavelength. We present new Magellan observations of two gravitationally lensed quasars: MG 0414+0534 and SDSS J0924+0219. We also analyse two epochs of Q2237+0305 data obtained from the literature. Our results are compared with four fidicial accretion disc models. At the 95 per cent level, only SDSS J0924+0219 is inconsistent with any of the accretion disc models. When we combine the results from all three quasars -- a first step towards assembling a statistical sample -- we find that the two steepest accretion disc models are ruled out with 68 per cent confidence. / In addition, we are also able to use our microlensing simulations to constrain the smooth matter percentages in the lenses at the image positions. In both MG 0414+0534 and SDSS J0924+0219 we find smooth matter percentages that are inconsistent with zero. A smooth matter percentage of approximately 50 per cent is preferred in MG 0414+0534, and approximately 80 per cent in SDSS J0924+0219. Q2237+0305 is usually assumed to have a smooth matter percentage of zero at the image positions, as they lie in the bulge of the lensing galaxy. Though our measurement is consistent with a zero smooth matter percentage, there is a peak in the probability distribution at a value 20 per cent. This is perhaps a hint of additional intervening structures along the line of sight to the background quasar. / We test the sensitivity of our accretion disc constraints to a range of modelling parameters. These include errors in lens modelling, Bayesian prior probability selection, errors in observational data, and the microlens mass function. Constraints on the power-law index relating source radius to observed wavelength are found to be relatively unaffected by changes in the modelling parameters. Constraints on source radii are found to be more strongly affected. / Finally, the broad emission line region of Q2237+0305 is examined. Gemini IFU observations are presented clearly showing differential microlensing across the velocity profile of the CIII] emission line. To analyse this signature, we present three simple broad emission line region models: a biconical outflow, a Keplerian disc, and spherical infall. A method is developed to compare the shapes of simulated flux ratio spectra with the observed spectrum. We are unable to discriminate between the biconical outflow and Keplerian disc models when we average over all viewing angles and orientations. The spherical infall model, however, does not fit the observed data. We also find that for the non-spherically symmetric geometries, low inclination angles are essentially incompatible with the observations. This analysis offers hope that with sufficiently high signal-to-noise observations, differential microlensing signatures may allow us to constrain the geometry and kinematics of this poorly understood portion of quasar structure.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 113-116). Also available for download via the World Wide Web; free to University of Oregon users.

Gravitational waves are predicted by Einstein’s general theory of relativity and have so far only been indirectly detected. The first direct detection should however only be a matter of time, with observatories across the world working hard to detect them. Once gravitational waves are detected they are predicted to be very useful in the field of astronomy. In order to be able to successfully interpret measurements from gravitational waves we need to have knowledge of how the wave is affected by its medium of propagation. Because of that, the purpose of this thesis is to investigate the behaviour of gravitational waves in the medium of a magnetised plasma. Using a kinetic plasma model, Einstein’s field equations and tetrad formalism, a general solution for a gravitational wave propagating in the medium is derived. The general solution is then used to find the dispersion relation of the gravitational wave for two special cases: the case of Alfvén resonance and the case of cyclotron resonance. The Alfvén case is already studied in the literature and is found to match the previous results saying it will not affect the wave much. The cyclotron resonance case is new and was chosen it can magnify the effects of the particles on the gravitational wave. The cases are studied with regards to detectability of a medium induced dispersion. The influence on the gravitational wave propagation is, however, found to be too small for dispersive effects to be detected in the cases studied / Gravitationsvågor förutses i Einsteins allmänna relativitetsteori och har så här långt endast blivit indirekt detekterade. Den första direkta detektionen är dock bara en tidsfråga och observatorier runtom i världen arbetar hårt för att lyckas med den. Då gravitationsvågor väl är detekterade sägs de ha stor potential inom astronomi. För att man ska kunna tolka mätdata från gravitationsvågor behöver man veta hur vågen beter sig i propagationsmediet. Av den anledningen är syftet med detta examensarbete att undersöka hur gravitationsvågor beter sig i ett magnetiserat plasma. Med hjälp av en modell för kinetisk plasma, Einsteins fältekvationer och tetradformalism härleds en allmän lösning för en gravitationsvåg som propagerar i en magnetiserad plasma fram. Lösningen används därefter för att hitta dispersionsrelationen för gravitationsvågen givet två specialfall: fallet för Alfvénresonans och fallet för cyklotronresonens. Alfvénfallet är redan studerat i tidigare litteratur och resultatet man hittar visar sig stämma överens med det tidigare funna resultatet som säger att det inte har en märkbar påverkan på vågen. Cyklotronresonansfallet är nytt och valdes eftersom att det kan förstärka de effekter som partiklarna har på gravitationsvågen. De båda specialfallen studeras närmare med avseende på detektion av en dispersion inducerad av mediet. Påverkan på gravitationsvågens propagation sluts dock till att vara för liten för att den ska bli uppmätt i de undersökta fallen.

Gravitational lensing, initially a phenomenon used as a solid confirmation of General Relativity, has defined itself in the past decade as a standard astrophysical tool. The ability of a lensing system to produce multiple images of a luminous source is one of the aspects of gravitational lensing that is exploited both theoretically and observationally to improve our understanding of the Universe. In this thesis, within the field of multiple imaging we explore the case of maximal lensing, that is, the configurations and conditions under which a set of deflecting masses can produce the maximum number of images of a distant luminous source, as well as a study of the value for this maximum number itself. We study the case of a symmetric distribution of n-1 point-mass lenses at the vertices of a regular polygon of n-1 sides. By the addition of a perturbation in the form of an n-th mass at the center of the polygon it is proven that, as long as the mass is small enough, the system is a maximal lensing configuration that produces 5(n-1) images. Using the explicit value for the upper bound on the central mass that leads to maximal lensing, we illustrate how this result can be used to find and constrain the mass of planets or brown dwarfs in multiple star systems. For the case of more realistic mass distributions, we prove that when a point-mass is replaced with a distributed lens that does not overlap with existing images or lensing objects, an additional image is formed within the distributed mass while positions and numbers of existing images are left unchanged. This is then used to conclude that the maximum number of images that n isolated distributed lenses can produce is 6(n-1)+1. In order to explore the likelihood of observational verification, we analyze the stability properties of the symmetric maximal lensing configurations. Finally, for the cases of n=4, 5, and 6 point-mass lenses, we study asymmetric maximal lensing configurations and compare their stability properties against the symmetric case.