Ph.D Student | Iya Tokarev |
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Subject | Applications of General Relativity in Astrophysics and Cosmology |

Department | Department of Physics |

Supervisor | Full Professor Nusser Adi |

Full Thesis text |

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.