M.Phil / MS
Permanent URI for this collectionhttps://repository.cuilahore.edu.pk/handle/123456789/52
This collection archives the complete set of theses produced by students of the COMSATS University Islamabad, Lahore Campus.
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Item Effects of Modified Entropy on Black Hole Thermodynamics in Bumblebee Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Zainab Nazish; CIIT/SP24-RMT-019/LHR; Dr. Abdul Jawad; LHR TP 10080This thesis explores the thermodynamic behavior and stability of anti-de Sitter (AdS) black holes within the framework of bumblebee gravity, a theory in which Lorentz symmetry is spontaneously broken by a vector field. The study examines how the Lorentz-violating bumblebee parameter influences the event horizon structure and various thermodynamic properties in both standard and extended phase spaces. Thermal stability is analyzed through heat capacity and Helmholtz free energy. The results show that large bumblebee AdS black holes can simultaneously satisfy local and global stability conditions, with the stable regions strongly depending on the Lorentz-violating parameter. The research also investigates heat capacity at constant pressure in the extended phase space, where the cosmological constant is interpreted as thermodynamic pressure. In this case, the stability criteria are found not to be fulfilled, highlighting the significant role of Lorentz symmetry violation in black hole thermodynamics. In addition, the thesis studies the sparsity parameter and Hawking radiation emission rates for black hole solutions in bumblebee gravity using generalized entropy models, including Sharma–Mittal entropy and three-parameter entropy indices. The findings reveal that changing the sign of the cosmological constant significantly affects thermodynamic sparsity and entropy behavior. A negative cosmological constant reduces sparsity while increasing entropy, indicating a denser thermodynamic system. Conversely, a positive cosmological constant preserves higher thermodynamic sparsity. Furthermore, the emission spectrum becomes sharper for negative cosmological constant values, indicating enhanced low-energy emission within a confining AdS background, while a positive cosmological constant generally suppresses the emission rate.Item Thermodynamic Phase Transitions of Black Hole Through Modified Entropy(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Ameer Hamza; CIIT/SP24-RMT-007/LHR; Dr. Abdul Jawad; LHR TP 10070In this thesis, we investigate charged black hole through the framework of Bekenstein- Hawking entropy and modified exponential entropy. These entropies are selected for their direct proportionality to the black hole’s horizon area and its natural derivation from Ein- stein’s field equations. The Bekenstein–Hawking entropy is a universally accepted and geometrically well-defined measure that is directly proportional to the area of the event horizon. On the other hand, the exponential entropy enhances the classical framework by integrating non-extensive and correlation effects inherent to gravitational systems, facili- tating regulated deviations from conventional thermodynamics. These two entropies offer both theoretical precision and practical flexibility in the analysis of black hole thermody- namics. We consider the Davies phase transition formalism, and discuss the stability of a black hole in its respective space and calculate its topological properties for dynamic stability. The expressions for mass, temperature, specific heat and divergence points are calculated. Also, we calculate the winding number an total topological charge with the help of phase portraits to discuss the local stable behavior of under consideration black hole for both entropy expression.Item Cosmic Implications of Tsallis Holographic Dark Energy with Various IR Cutoffs in Horava- Lifshitz Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Mehwish Shad; CIIT/SP20-RMT-024/LHR; Dr. Abdul Jawad; LHR TP 7653Horava-Lifshitz gravity is a very fascinating proposal of modified gravity for explaining the current acceleration and other cosmic issues. In contin- uation of this discussion, we study the consequences of Tsallis dark energy with Hubble and particle horizons in the framework of deformed Horava- Lifshitz gravity by taking into account flat FRW universe. The interaction between Tsallis holographic dark energy and dark matter are also taken into account to discuss the underlying scenario. It is found that fractional dark energy density (ΩD) approaches to 0.70+0.03 −0.03 as redshift goes to zero (present epoch) for both cases of horizons. The cosmic parameter (ωD) shows phantom crossing behavior in both models, i.e., it evolutes the uni- verse from quintessence phase to phantom phase by crossing the vacuum horizon. In both cases of horizons, the deceleration support the cosmic ac- celeration by exhibiting the negative values. The perturbation sound speed also favors the viability of our models through positive behavior. The co- incidence parameter support the exchange of dark matter to dark energy phenomenon through positivity. We also discuss the behavior of growth rate and growth index in the growth of matter density perturbations for both horizons. These parameters mimic the ΛCDM behavior of the universe.Item Cosmic Acceleration in Modified Horava- Lifshitz Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Sameen Ashraf; CIIT/FA19-RMT-094/LHR; Dr. Abdul Jawad; LHR TP 7395We discuss the cosmological implications of the interacting Barrow holo- graphic dark energy model in the context of flat deformed Hoˇrava-Lifshitz gravity by assuming the interaction (Γ) between dark energy and pressure- less dark matter. To understand the mechanism of recent accelerated ex- pansion of the universe, we consider Hubble and event horizons as infrared cutoff. We investigate the evolutionary history of cosmological parame- ters especially the equation of state, Hubble, deceleration, squared speed of sound and find results that favor observational data of Planck 2018. It is found that the Hubble parameter lies in the range 72+2 −2 (for event horizon) and 74.004+0.004 −0.004 (for Hubble horizon). The equation of state parameter pro- vides the phantom phase of the universe, while the deceleration parameter illustrates the accelerated phase of the universe. On the other hand, we plot the squared speed of sound and find the positive behavior which ensures the stability of underlying model. Moreover, we examine the generalized second law of thermodynamics of this cosmological system with barrow entropy as horizon entropy and observe that this law holds for both horizons.Item Geometric Thermodynamics of Well-Known Black Holes(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Syeda Rabab Fatima; CIIT/FA19-RMT-111/LHR; Dr. Abdul Jawad; LHR TP 7532We study the phase transition and thermodynamic geometries of a charged AdS black hole with a global monopole. For this purpose, we develop the thermodynamic quantities such as Hawking temperature, spe- cific heat and pressure on horizon radius in the presence of Barrow entropy. The stability of this black hole is being observed through specific heat. Also, we investigate the thermodynamic curvatures behavior of black hole by applying Weinhold and Ruppiner formulations. It is found that ther- modynamic curvatures exhibit the attractive and repulsive nature of black hole for specific constants. We also study the thermodynamic curvature of charged BTZ black hole by fixing phase space of entropy, pressure and volume on curvature, i.e., entropy-pressure corrected curvature (RSP ) and entropy-volume corrected curvature (RSV ). It is found that there present a repulsive force by the charged BTZ black hole for its molecules, qual- itatively or phenomenologically. However, RSV shows negative behavior initially which exhibits the attractive nature of charged BTZ black hole.Item Cosmic Inflation Evading Swampland Conjectures(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Kashaf Embreen; CIIT/FA19-RMT-022/LHR; Dr. Abdul Jawad; LHR TP 7440In this thesis, we study the inflationary scenario in the realm of k-essence model and swampland conjecture. Taking into account three models of Chaplygin gas, that is, generalized, modified and generalized cosmic Chap- lygin gas models, we discuss the slow roll parameters (²(φ), η(φ)), curvature perturbation (Ps), tensor to scaler ratio (r) and scaler spectral index (ns). In reference to k-essence model, the coupling function as a function of scaler field L(φ) is used. We investigate the swampland conjecture and then find the value of ζ(φ) i.e bound of second conjecture for the above three models by unifying swampland conjecture and k-essence. We plot the inflationary parameters and bound of swampland conjecture r −ns, ζ(φ) − φ, and check their values according to Planck data 2018.Item Dynamical Properties of Specific Black Holes(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2017) Muhammad Umair Shahzad; CIIT/FA13-PMATH-005/LHR; Dr. Abdul Jawad; LHR TP 5606The 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.Item Cosmological Consequences of Some New Versions of Dark Energy Models(COMSATS University Islamabad, Lahore Campus Library Information Services, CUI Lahore, 2019) FA17-RMT-046; Sabir Hussain,; Dr. Abdul Jawad, Assistant Profesor [Supervisor]; LHR TP 5667it is observed that the universe expanding with repulsive force. Dark en ergy is an unknown force and responsible for current cosmic acceleration. Generally, in order to find the best-fit model to discuss the cosmic accel eration and dark energy phenomenon, there are two directions that are dynamical dark energy models and modified theories of gravity. One of the dynamical model is holographic dark energy which is also modified in different forms such as modified, generalized, Tsallis, Renyi, Sharma Mittal holographic dark energy models, etc. The modified theories include fractal cosmology, Dvali-Gabadadze-Porrati braneworld, second Randall Sundrum braneworld, loop quantum cosmology, dynamical Chern-Simons gravity, f(R), f(T), f(R,T) theories of gravity etc. Taking some of these models and theories, researchers established different cosmological parame ters.In this thesis, we use Tsallis holographic dark energy model with gen eralized ghost pilgrim dark energy as infra-red cutoff for modified theo ries of gravity such as cyclic universe, Dvali-Gabadadze-Porrati braneworld, Randal-Sundrum II braneworld and dynamical Chern-Simons theory in the fat Friedmann-Robertson-Walker universe. In these directions, we study some cosmological parameters like equation of state, deceleration parame ter, squared sound speed and Om (combination of Hubble and cosmos red shift parameter) parameter. We also establish some cosmic planes such as ω −ω and r−s on the basis of present day observational data.Item Swampland Criteria of Inflationary Cosmology with Well-Known Potentials(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Aneesa Majeed; CIIT/FA19-RMT-115/LHR; Dr. Abdul Jawad; LHR TP 7383We explore the swampland conjectures of quintessence and tachyon scalar field models in f(T ) and Einstein gravities, respectively. In f(T ) gravity, we consider cold and warm (by assuming generalized dissipative coefficient) inflationary scenario and develop constraints on de-Sitter con- jectures through Bekenstein entropy relation. In usual inflation, the de- Sitter conjecture constraint becomes constant (in terms of models constant parameters) which can be easily analyzed for its validity (i.e., |V 0| V ≤ O(1)). However, in warm inflation, we analyze the de-Sitter conjecture constraint through T 0V TV 0 , i.e., if T 0V TV 0 < 1 then |V 0| V ≤ O(1) and hence we can obtain required result. For evaluating this condition, we choose three well-known potentials such as monomial chaotic, hilltop and generalized exponential. It is observed that the condition T 0V TV 0 < 1 satisfied for all three potentials in both regimes of dissipative coefficient for specific choice of constants. Sim- ilarly, we also obtain satisfactory results of de-Sitter conjecture for tachyon and polytropic (with quintessence scalar field) in general relativity.Item Thermal Fluctuations Of A Regular And Einstein(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2016) Hafiza Zarish Arshad; , FA14-BSM-001; Dr. Abdul Jawad, Assistant Profesor; LHR TP 5252In this thesis, we study the effects of thermal fluctuations on regular black hole solutions with cosmological constant and Einstein-aether black hole with coupling constant respectively. We consider the logarithmic corrected entropy in order to analyzing the thermal fluctuations on regular black hole solutions and Einstein-aether black hole. We also obtain various thermo dynamical quantities such as entropy, pressure, specific heats, Gibb’s free energy and Helmholtz free energy. We also investigate the stability of reg ular black hole solution and Einstein-aether black hole in terms of γ, phase transition, grand canonical ensemble and canonical ensemble. We analyze that regular black hole are stable when we increase the value of cosmologi cal constant and Einstein-aether black hole are stable when we increase the value of coupling constant respectively.