Browsing by Author "Dr. Shamaila Rani"

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Analysis of Barrow Holographic Dark Energy in Five- Dimensional Modified Gravity
(Library Information Services, CUI Lahore, 2022) Warisha; FA21-RMT-043; Dr. Shamaila Rani
In this thesis, we assume FRW universe in context of ¯ve-dimensional Einstein Chern-Simons theory of gravity. The Barrow holographic dark energy density with Hubble horizon as boundary of the universe is taken into account to study cosmic evolution of the universe. We discuss some cosmological parameters such as coincidence parameter, density parame- ter, EoS parameter and deceleration parameter. Moreover, we also discuss the thermal stability in context of underlying scenario. We plot coinci- dence parameter which exhibit a DE dominated phase of the universe. We consider Barrow holographic dark energy model with both interacting and non-interacting scenario of dark components to evaluate these parameters and thermal stability. It is mentioned here that we obtain some consistent results representing accelerated expansion of the universe.
Analyzing Various Aspects of Black Holes in Modified Gravity
(Library Information Services COMSATS University Lahore Campus, 2024-03-18) Muhammad Arslan Nasir; SP23-RMT-019; Dr. Shamaila Rani; LHR TP 9575
In this thesis, we investigate the thermodynamic properties of the Bardeen-Kiselev black hole solution with a cosmological constant, focusing on stability, phase transitions, and the compressibility factor using generalized entropy corrections. By incorporating Bar row, Renyi, Sharma-Mittal, Kaniadakis, and loop quantum gravity entropy corrections, we ´ explore their impact on black hole stability and phase transitions through specific heat ca pacity, pressure, compressibility, and Helmholtz free energy. The analysis reveals that spe cific heat capacity exhibits distinct behaviors across entropy models, including regions of stability (positive specific heat), instability (negative specific heat), and divergence points indicating phase transitions. For instance, Barrow entropy shows stability for small black holes (BHs), phase transitions for intermediate BHs, and restabilization for larger BHs. Loop quantum gravity entropy highlights significant phase transitions with unique stability patterns at higher horizon radii. Pressure-volume graphs illustrate how entropy corrections influence the black hole’s equation of state. Smaller BHs often exhibit instability at low volumes, transitioning to stable phases as volume increases. Notably, the Barrow and Sharma-Mittal entropy models show smooth transitions, whereas Kaniadakis and loop quantum gravity entropy correc tions reveal more abrupt changes. The compressibility factor analyses further underscore the non-ideal thermodynamic behavior of black holes under these entropy corrections. While Barrow entropy maintains compressibility near zero, Kaniadakis and loop quan tum gravity corrections exhibit exponential divergences, highlighting significant deviations from classical thermodynamics. Finally, Helmholtz free energy graphs demonstrate entropy-corrected phase transitions ix and stability trends. Smaller BHs exhibit consistent phase shifts across all models, with larger BHs progressively stabilizing under increasing pressure. Comparative analysis indi cates that Barrow entropy provides higher stability for larger BHs, while Sharma-Mittal and loop quantum gravity corrections lead to more dynamic transitions. This comprehensive study enriches the understanding of black hole thermodynamics by bridging classical and quantum gravity perspectives. By interpreting the cosmological constant as pressure and incorporating entropy corrections, this work offers insights into black hole stability, phase transitions, and their connections to statistical mechanics and quantum gravity frameworks. These findings contribute to the broader understanding of black hole behavior in general relativity and beyond.
Barrow Holographic Dark Energy in Extended Teleparallel Theories of Gravity
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Ghulam Murtaza; CIIT/FA19-RMT-085/LHR; Dr. Shamaila Rani; LHR TP 7424
In this thesis, we reconstruct some solutions in the context of telepar- allel based extended theories coupled with trace of energy-momentum ten- sor, boundary term and Gauss-Bonnet term. For this purpose, we ob- tain the eﬀective energy density and pressure for these theories for ﬂat FRW universe model. The reconstruction is made through the compari- son of these eﬀective energy densities with the energy density of Barrow holographic dark energy model. In this regards, we use scale factor in terms of power-law form and ﬁnd some gravitational Lagrangian functions as f(T ) = T +g(T ), f(T, τ ) = T +γh(τ ), f (T, τ ) = βτ +g(T ), f(T, TG) = TGg(T ), f(T, TG) = −T + TGg(T ), f(T, TG) = TG + g(T ), f(T, TG) = T + j(TG), f(T, B) = T + σy(B) and f(T, B) = B + ξg(T ). In order to discuss the cosmic analysis related to these models, we plot equation of state parameter for each model. We investigate the squared speed of sound parameter for these models to determine the stability of the models. We obtain some favorable results related to speciﬁc values of model parameters.
Cosmic Expansion Phenomenon in Specific Scalar Field Theory
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Farwa Khurshid; CIIT/FA19-RMT-105/LHR; Dr. Shamaila Rani; LHR TP 7430
The interaction of newly proposed holographic dark energy model, Bar- row holographic dark energy model is being used to analyze the cosmic expansion phenomenon. We consider the interaction between dark energy and dark matter in the realm of scalar ﬁeld theory. For the power law, quadratic and quartic (positive and negative) potentials, we investigate the diﬀerent cosmological implications. This includes the equation of state pa- rameter ωD which identiﬁes diﬀerent eras of the expanding universe, cosmic plane ωD − ω0 D (where ω0 D shows the evolution of equation of state para- meter ωD where prime shows derivative with respect to ln a) and squared speed of sound parameter v2 s for the stability analysis of the models.
Cosmic Thermodynamics of Matter Creation Models in Alternative Theories of Gravity
(LHR TP 6477, 2020) Farzan Mushtaq; SP19-RMT-021; LHR TP 6477; Dr. Shamaila Rani
This thesis is devoted to study some cosmological models in the scenar- ios of two gravitational theories like fractal universe model and dynamical Chern-Simons modi¯ed theory in particle creation mechanism. In the case of fractal universe model, we consider particle creation rate as constant and variable with two models. We use Gibbs equation to ¯nd out pressure of particle creation rate adiabatic matter phenomenon. For these cases, cosmological parameters like e®ective equation of state and deceleration parameter are studied. Also, we investigate the behavior of generalized sec- ond law of thermodynamics for Barrow entropy by taking constant particle creation rate. For dynamical Chern-Simons theory, two variable particle creation rate models are used for which we explore e®ective equation of state parameter and deceleration parameter.
Cosmographic and Matter Bounce Scenario in Modified Torsion Gravity
(Library Information Services, CUI Lahore, 2023) Sidra Karim; FA21-RMT-032/; Dr. Shamaila Rani
FRW universe, we consider the functional form f (T; ¿ ) = ®¿ + °T 2, where ® and ° are adjustable parameters. We examine the cosmological behavior of the deceleration parameter and the equation of state parameter, which demonstrate a transition from deceleration to acceleration. Additionally, we explore a bouncing universe scenario in modi¯ed f (T; ¿ ) gravity. We study two distinct scale factor models, both of which are non-zero at the point of bounce (t = 0) and can resolve the singularity problem. We present the behavior of the Hubble parameter H and the deceleration parameter q, energy conditions (null energy condition and strong energy condition) and stability of both models at the point of bounce. Secondly, we consider an- other torsion based theory named as non-zero torsion gravity to discuss the cosmographic analysis. For this purpose, the evolutions of the deceleration parameter q(z), jerk parameter j(z), snap parameter s(z), lerk parameter l(z) and EoS parameter !D with respect to redshift z are reconstructed.
Cosmological Analysis of Reconstructed Einstein-Aether Models
(Library Information Services, COMSATS University, Lahore Campus, 2018) Irfan Ullah Malik; SP 17-RMT-007; Dr. Shamaila Rani
In this thesis, we reconstruct various solutions for the accelerated universe in the Einstein-Aether theory of gravity. For this purpose, we obtain the effective density and pressure for Einstein-Aether theory. We reconstruct the Einstein-Aether model parameter by comparing its energy density with various holographic dark energy models such as Tsallis, R´enyi and Sharma Mittal holographic dark energy models. For this reconstruction, we use two forms of scale factor, power-law and exponential forms. The cosmological analysis of underlying scenario has been done by exploring different cos mological parameters. This includes equation of state parameter, squared speed of sound and evolutionary equation of state parameter via graphical representation. We obtain some favorable results for some model parametric values
Cosmological and Dynamical Instability Analysis in Some Modified Theories of Gravity
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Tanzeela Nawaz; CIIT/FA13-PMATH-007/LHR; Dr. Shamaila Rani; LHR TP 7732
The present thesis comprises the study of three dynamical phenomena such as evolution of the universe through cosmological parameters, thermodynamics via the generalized second law of thermodynamics and dynamical instability of collapsing star taking into account adiabatic index. Firstly, we consider a new holographic dark energy model in the framework of dynamical Chern-Simons modified theory of gravity to explore various cosmological parameters (like equation of state, squared speed of sound, Om-diagnostic) and cosmological planes ( d d  ' where d ' is the evolutionary equation of state parameter, statefinders). We examine their graphical results and also comprise with the different observational data like Planck, 0 H , SNLS and WMAP. Secondly, the thermodynamics through generalized second law of thermodynamics in the framework of dynamical Chern-Simons theory of gravity by taking interaction between dark energy and dark matter is discussed. In the first part, we discuss the scalar field phenomenon of dark energy model having a non-canonical kinetic term in the flat universe and investigate the stability of the model through squared speed of sound. The generalized second law of thermodynamics by taking usual entropy and its correction forms like logarithmic and power law at apparent horizon is studied. In second part, this law is investigated by taking the interaction of dark matter and dark energy with holographic dark energy model and different cutoffs like Hubble horizon, event horizon, their combination, Ricci scalar and its generalized form. The generalized form of second law of thermodynamics in terms of coincidence parameter is being evolved. Next, we choose the framework of modified Brans-Dicke gravity to study generalized second law of thermodynamics by developing the expressions tot S ' for usual entropy as well as its corrected forms, logarithmic and power law corrected on the apparent and event horizons. Also, the power law forms of scalar field and scale factor are utilized in order to analyze the clear view of thermodynamic law. Finally, we find the instability ranges of spherical and cylindrical symmetric structures of a collapsing object in FT, theory where, T denotes the torsion scalar and  is the trace of energy-momentum tensor. The perturbation method is used upto first order in the modified field equations to construct dynamical collapse equations. These equations with adiabatic index are utilized to check the instability ranges in Newtonian and post-Newtonian limits. It is found that the instability ranges depend on the dynamical variables of collapsing object.
Cosmological Consequences of Equation of State Parameterizations in Mimetic Gravity
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Muhammad Rizwan Azhar; CIIT/FA20-RMT-032/LHR; Dr. Shamaila Rani; LHR TP 7935
This thesis is devoted to study the cosmic aspects of the evolving uni- verse by taking into account mimetic gravity. Mimetic gravity is a Weyl- symmetric expansion of general relativity linked by a single disformal trans- formation, in which the presence of a dust-like perfect ﬂuid may be used to imitate cold dark matter on a cosmic scale. We consider three well-knows equation of state parameterizations in terms of redshift function. Using mimetic gravity energy density, we calculate the potential, coincidence pa- rameter and deceleration parameter for all parametrization models with the help of energy conservation equation, Lagrange multiplier and normal- ized Hubble parameter. Considering the observational values of parameters in parametrization models, we get some useful results for the underlying scenario.
Cosmological Consequences of Extended Bose Einstein Condensate Dark Matter in Specific Modified Gravity
(Library Information Services COMSATS University Lahore Campus, 2023-03-13) Hafiz Haseeb Nawaz; SP22-RMT-005; Dr. Shamaila Rani; LHR TP 8713
In this manuscript, we consider the newly proposed modified theory in which topological invariant Gauss-Bonnet G is coupled with the energy momentum squared (τ 2 = τµντ µν). For this matter-geometric coupling, we consider f(G, τ 2 ) = f(G) + g(τ 2 ) model for flat FRW universe. The dy namics of bouncing cosmology are thoroughly examined within the frame work of underlying viable model,can overcome the singularity’s challenge in standard Big-Bang cosmology. We study power law scale factor and some cosmological bouncing scale factors such as the four types of bounces are matter, oscillatory, super, and symmetric.In this scenario,the equation of state parameter is computed ω and the squared sound speed parameter. We also check the dynamics of ω −ω 0 plane for underlying framework. Interest ingly, it should be noted that every outcome favor the recent observational data.
Dynamical Stability of Modified Friedmann Equation Through Non-Linear Interactions
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Muhammad Husnain Tariq; CIIT/SP24-RMT-013/LHR; Dr. Shamaila Rani; LHR TP 10074
In this thesis, we discuss the dynamical stability scenario in the framework of dynamical Chern-Simons modified theory of gravity. In this regards, we develop six models with nonlinear interactions in the theoretical framework of dynamical Chern-Simons modified gravity and apply the dynamical system analysis to investigate their dynamical stability with phase portraits. These nonlinear interactions are considered through energy conser- vation equations between dark energy and dark matter. We find the dynamical system in terms of autonomous system of differential equations of fractional energy densities of dark energy and dark matter with respect to e-fold number of the universe. This system of equa- tions depends on equation of state parameters related to matter and dark energy and yields the critical points for each interacting model. We consider three cases for matter equation of state as radiation, pressure-less, stiff fluid with various values of dark energy equation of state parameter representing current accelerated expansion of the universe and specific value of interaction parameter. The eigenvalues at each critical point are evaluated and the stability is verified by signs of eigen values. Furthermore, the attractor behavior for sta- ble critical point and repulser behavior for unstable state are discussed through the phase portrait analysis.
Effects of Exponential Entropy on Thermodynamic Geometries
(Library Information Services, CUI Lahore, 2023) Sadaf Iqbal; FA21-RMT-030; Dr. Shamaila Rani
This thesis delves into the analysis of thermodynamics of a 5-D Schwarz- schild AdS black hole(BH) within the AdS5 £ S5 spacetime, incorporatingexponential entropies. The conventional understanding of ¤ (cosmological constant) as thermodynamic pressure, with volume being its counterpart, cannot be directly applied in the framework of the AdS/CFT correspon- dence. Instead, we establish a connection between the ¤ in the boundary gauge theory and N (number of colors), where the thermodynamic conju- gate is represented by the chemical potential. In this study, we replace the geometric parameters L and r of the AdS black hole with two thermody-namic parameters N 2 and S in the micro canonical ensemble. Additionally, we valuate various formulations of thermodynamic geometry, such as Rup- peiner, Quevedo and Weinhold, and derive the associated scalar curvatures for the 5-D Schwarzschild AdS BH. We see these geometries exhibit attrac- tion/repulsion forces on particles.
Effects of Modified Entropies on Geometric Thermodynamics of Black Holes
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Aqsa Tanveer; CIIT/SP20-RMT-011/LHR; Dr. Shamaila Rani; LHR TP 7647
In this thesis, we analyze the thermodynamics of ﬁve-dimensional Schwarz- schild AdS black hole in AdS5 × S5 spacetime in the presence of Tsallis entropy. Since the cosmological constant Λ is considered as thermodynam- ical pressure with volume as its conjugate, but this explanation cannot be employed in AdS/CFT correspondence. In this study, we associate cosmo- logical constant Λ in boundary Gauge theory with the number of colors N and chemical potential is taken to be its thermodynamic conjugate. The two geometric parameters in the AdS black hole, r and L are substituted for two thermodynamic parameters in the micro-canonical ensemble, which are considered to be entropy S and N2. Moreover, we evaluate several thermodynamical geometry formulations, including Weinhold, Ruppeiner, and Quevedo and derive associated scalar curvatures for ﬁve-dimensional Schwarzschild AdS black hole
Growth of Matter Index and Cosmic Acceleration
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Amir Sharif; SP19-RMT-039; LHR TP 6485; Dr. Shamaila Rani
In the framework of dynamical Chern-Simons theory of gravity, we study the recent cosmic expansion with acceleration of the universe. We take in teracting scenario of dark energy and dark matter with three cutoffs like Granda-Oliveros, higher order derivative of Hubble parameter and gener alized holographic dark energy model. In the flat Friedmann-Robertson Walker universe, well-known cosmological parameters have been calculated. We study the perturbation of matter density growth, growth factor and growth index behavior for the underlying framework. The cosmological pa rameters like equation of state parameter, deceleration parameter, fractional generalized holographic dark energy density and stability of each model are discussed. The outcomes of these models represent the cosmic expansion of the universe with acceleration
Impact of alternative theories of gravity on current cosmic scenarios
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Nadeem Azhar; CIIT/FA17-PMT-013/LHR; Dr. Shamaila Rani; LHR TP 7861
This thesis incorporates the study of some current cosmic scenarios in the realm of alternative theories of gravity (curvature and torsion based theories). These scenarios include gravitational baryogenesis phenomenon, cosmic accelerating expansion of the universe and thermodynamic analysis. Firstly, we examine the matter-antimatter asymmetry through the gravitational baryogenesis and its generalized mechanisms for some well-known curvature and torsion-based models. The absence of intense radiation from matter/anti-matter annihilation, cosmic microwave background and big bang nucleosynthesis strongly suggested that there exists more matter than anti-matter in our universe. Observational constraints verified that the baryon number density 𝜂𝐵 to entropy 𝑆 ratio is approximately 𝜂𝐵 𝑆 ∼ 9.42 × 10−11. We compute the baryon to entropy ratio for all models and get some consistent results. Secondly, we investigate the evolution of some cosmic parameters and planes in the framework of DGP braneworld model. We assume interaction between Barrow holographic dark energy model (whose infrared cutoffs scale are set by Hubble and event horizons) and pressureless dark matter. We check the behavior of different cosmological parameters like Hubble, equation of state, deceleration, squared speed of sound, statefinder plane and 𝜔𝜗 − 𝜔𝜗 ′ plane. Also, the thermodynamic nature of the underlying model through Barrow entropy as horizon entropy is investigated. Finally, we consider Tsallis holographic dark energy model with event and apparent horizons as infrared cutoff in the framework of dynamical Chern-Simons modified gravity. The impact of non-flat FRW universe is being taken into account to explore some cosmological parameters like Hubble, equation of state, deceleration and squared speed of sound. Finally, we investigate the generalized second law of thermodynamics with Tsallis entropy for both horizons and find some interesting outcomes.
Inflationary Parameters and Swampland Conjectures in Various Scenarios of Gravity
(Library Information Services COMSATS University Islamabad Lahore Campus, 2022) Shama Sadiq; FA20-RMT-019; LHR TP 7923; Dr. Shamaila Rani
The purposeofthisthesisistoinvestigatethein°ationaryparameters and swamplandconjecturesinthepresenceofscalar¯eldandChaplygin gas models.Weinvestigatethein°ationaryparameterssuchasslowroll parameters, scalarpowerspectrum,tensorpowerspectrum,spectralin- dex, tensor-to-scalarratiointhepresenceofscalar¯eldandChaplygingas modelsandalsodiscusstherecentlyproposedswamplandconjectures.The in°ationary scenarioisassumedtobeworkingunderastandardscalar¯eld having¡asdecayratio.Thisdecayratiohasdependenceintheformof generic power-lawofscalar¯eld Á along withthermalbathtemperature T, that is,¡(Á; T) = CÁ Ta Áa¡1 , where CÁ is dimensionlessparameterand a is in°ation decayrate.Assumingthatourmodelbendsaccordingtostrong dissipativeregime(R À 1), westudythebackgroundandperturbativedy- namics aswellasin°ationaryobservableasthescalarpowerspectrum PR, scalar spectralindex ns, dissipativeratio R, thetensor-to-scalarratio r, run- ning ofthescalarspectralindex dns d ln k and generalizedratioofSwampland de-Sitter conjecture ¶ TV ¶ V T for threedi®erentpotentials V (Á) = 3H2inf 8¼ e 2Á p(Á+1) , V = M4µ Á Mp¶2µ1 + ¯ Á2 M2p ¶ and V = 3 4M2(1 ¡ ep 2 3Á)2 respectively.
Insights of Modified Entropy on Therodynamics of Black Holes in Einstein Maxwell Scalar Theory
(Library Information Services COMSATS University Lahore Campus, 2024-03-17) Ayesha Siddiqa; FA22-RMT-050; Dr. Shamaila Rani; LHR TP 9383
Insights of Modified Entropy on Therodynamics of Black Holes in Einstein Maxwell Scalar Theory
Non-Linear Interaction of Dark Energy Models in Fractal Cosmology
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2020) Ayesha Sadiq; FA18-RMT-076; LHR TP 6037; Dr. Shamaila Rani
We investigate the cosmological aspects of various dark energy models in fractal universe by assuming non-linear interaction term between the dark energy and dark matter components. We work with three well-known models named as generalized ghost dark energy, power law corrected entropy and holographic dark energy. We investigate the cosmological parameters such as (deceleration parameter q, equation of state ωΛ, squared speed of sound, Om-diagnostic) and cosmological planes (ωΛ−ω´Λ, state-finder parameter). We explore these parameters graphically for the analysis of evolution of the universe. It is observed that by using different observational schemes the equation of state parameter gives consistent ranges. We check the model’s stability using the squared sound speed. In the present scenario, the squared speed of sound is stable for these three models. We also find the consistent results of the ωΛ − ω´Λ and statefinder planes with observational schemes.
Physical Aspects of Dark Universe Through Matter Growth Perturbations
(Library Information Services COMSATS University Lahore Campus, 2024-03-17) Aneela; Fa22-rmt-004; Dr. Shamaila Rani; LHR TP 9376
Physical Aspects of Dark Universe Through Matter Growth Perturbations
Squared Speed of Sound Parameterizations in Non- Zero Torsion Cosmology
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Iram Ashraf; CIIT/SP20-RMT-022/LHR; Dr. Shamaila Rani; LHR TP 7652
In this thesis, we use some squared speed of sound models in the frame- work of the non-zero torsion theory for ﬂat FRW spacetime. These squared speed of sound models depend on equation of state parameter. We dis- cuss the accelerated expansion of the universe through some cosmological parameters like Hubble parameter, deceleration parameter and stateﬁnder parameters. For deceleration parameter, we get some constraints to be fulﬁlled by model parameters for the sake of accelerated expansion of the universe. The stateﬁnder parameters show the ΛCDM limit as well as some consistent behavior for each model. We also check the validity of general- ized second law of thermodynamics and thermal equilibrium for each model by taking into account Bekenstein entropy. In terms of equation of state parameter having range of quintessence, cosmological constant as well as phantom era, we get some consistent results for particular values of model constants.