PhD

Permanent URI for this collectionhttps://repository.cuilahore.edu.pk/handle/123456789/50

This collection archives the complete set of theses produced by students of the COMSATS University Islamabad, Lahore Campus.

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Dynamical Properties of Specific Black Holes
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2017) Muhammad Umair Shahzad; FA13-PMATH-005; LHR TP 5606; Dr. Abdul Jawad
The present thesis comprises the study of three dynamical phenomenon such as thermal fluctuations, accretion and tidal forces of black holes/regular black holes. We consider the logarithmic corrected entropy in order to analyze the thermal fluctuations. We examine the effects of thermal fluctuations on a regular black hole of the non-minimal Einstein-Yang-Mill theory with gauge field of magnetic Wu-Yang type and a cosmological constant. We investigate the first law of thermodynamics in the presence of logarithmic corrected entropy and non-minimal regular black hole. Furthermore, we discuss the thermal fluctuation problem by utilizing the higher order corrected entropy. We examine the thermodynamical behavior of two well-known black holes such as Reissner-Nordström Anti de Sitter black hole with global monopole and f(R) black hole in the presence of higher order corrected entropy. We also discuss the accretion problem in two phases. In first phase, we analyze the accretion onto static spherically symmetric regular black holes for specific choices of the equation of state parameter. The underlying regular black holes are charged regular black holes using the Fermi-Dirac distribution, logistic distribution, non-linear electrodynamics, respectively, and Kehagias-Sftesos asymptotically flat regular black holes. In second phase, we develop the Hamiltonian dynamical system to tackle the accretion problem. We investigate the accretion of test fluids onto regular black holes such as Kehagias-Sftesos black hole and regular black holes with Dagum distribution function. We analyze the accretion process when different test fluids are falling onto these regular black holes. The behavior of fluid flow and the existence of sonic points is being checked for these regular black holes. Finally, we investigate the tidal forces occurring in a Kiselev black hole surrounded by radiation and dust fluids. We also solve the geodesic deviation equation for radially free-falling bodies toward Kiselev black hole. We explain the geodesic deviation vector graphically and point out the location of the event and Cauchy horizons for specific values of the radiation and dust parameters.
Study of Cosmic Acceleration and Thermodynamic Consequences in Alternative Theories of Gravity
(Library Information Services COMSATS University Islamabad Lahore Campus, 2021) Ayesha Iqbal; FA14-PMATH-002; LHR TP 7450; Dr. Abdul Jawad
In this thesis, we discuss two interesting issues: the accelerated expansion of the universe and thermodynamics. We consider flat Friedmann-Robertson-Walker universe model in alternative theories of gravity like loop quantum cosmology, Dvali- Gabadaze-Porrati brane world and fractal universe. We use different models of dark energy like Ricci Gauss-Bonnet dark energy and some latest holographic dark energy models namely Tsallis, Renyi and Sharma-Mittal holographic dark energy models for the analysis of both issues. For accelerated expansion of the universe, we examine the cosmological parameters like effective equation of state parameter, deceleration parameter, statefinder parameters, Om-diagnostic, plane of effective equation of state parameter with its evolutionary parameter and squared speed of sound parameter. We investigate the validity of the generalized second law of thermodynamics and thermodynamical equilibrium for the case of thermodynamic analysis. Firstly, we consider loop quantum cosmology and fractal universe in flat FRW universe with an interacting scenario between a non-canonical scalar field model of dark energy and dark matter. We make the analysis by using constant and variable (CPL parametrization) forms of equation of state parameters. We discuss the deceleration parameter for expansion rate along with squared speed of sound for stability analysis. Taking Bekenstein, logarithmic and power law entropies as the horizon entropy, we examine generalized second law of thermodynamics and thermal equilibrium. Secondly, we study the cosmological implications using Tsallis, Renyi and Sharma- Mittal holographic dark energy models in the interacting framework. We take into account two theories, fractal and Dvali-Gabadaze-Porrati brane world. We discuss the cosmological parameters and planes in both theories for the evolving universe. Finally, we examine the validity of generalized second law of thermodynamics of a physical system enveloped by apparent as well as event horizons. The system is comprised of Ricci Gauss-Bonnet dark energy and dark matter. We use various forms of entropy namely Bekenstein, Renyi, logarithmic and power law entropy corrections. We also examine the thermodynamic equilibrium in case of each entropy.