טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentTokarev Iya
SubjectApplications of General Relativity in Astrophysics and
Cosmology
DepartmentDepartment of Physics
Supervisor Professor Adi Nusser
Full Thesis textFull thesis text - English Version


Abstract

This work is concerned with problems in astrophysics and cosmology in the framework of general relativity. Some of the problems were previously examined in the literature in the context special relativity. We show that analysis based on general relativity produces results that are significantly different.In the first part of the work we study the conversion of neutron matter into strange matter. We show that a conversion of neutrons into strange quark matter in neutron stars is possible by means of a combustion process with a well-defined front. Conditions for the realization of a specific combustion mode, whether deflagration, detonation, or fast combustion, are derived for several forms of the  equations of state of neutron and strange matters. We assume that the process of the conversion occurs in the form of a detonation wave. The detonation is assumed to originate from a central region in a spherically symmetric background of neutrons with a radially varying density distribution. We present self-similar solutions for the propagation of detonation in static and collapsing backgrounds of neutron matter. The solutions are obtained in the framework of general relativistic hydrodynamics, and are relevant for the possible transition of neutron into strange stars. Conditions for the formation of either bare or crusted strange stars are discussed.The second part of this work focuses on models of the modern accelerated Universe.  We consider cosmological models with modification of the Einstein-Hilbert action by the correction f(R)~b|R|n. The model’s parameters are constrained by matching the evolution of the Universe after recombination resembles that of a flat Friedman-Robertson-Walker model with cold dark matter, the observed modern cosmic acceleration, and the measured large-scale matter power spectrum. Linear perturbations in f(R)-modified gravity are adopted to compute the model power spectrum. To simplify the calculations and the interpretation of the analysis, we use a conformal equivalence between the modified gravity and the Einstein gravity with non-minimally coupled scalar fields.In the third part of this work we consider the gauge-invariant perturbations in models describing the Universe as being filled by dark viscous fluid, in which bulk viscosity coefficient is a function of density. The analysis shows that the models are inconsistent with the observational data. Consideration of two fluid models that encompass dark viscous fluid as well as baryonic matter allows us to conclude that such models are good enough to describe the accelerated Universe including its galaxies and the large scale structure.