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.
Browse
3 results
Search Results
Item Warm Viscous Inflation Inspired by Modified Chaplygin Gas within Rastall Theory of Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Abdul Wahab; CIIT/FA19-RMT-107/LHR; Dr. Rabia Saleem; LHR TP 7396This thesis is a contribution to study the effectiveness of Rastall gravity (RG) to discuss warm viscous inflation inspired by modified Chaplygin gas. The mat- ter contents of our cosmos are taken to be standard scalar field (ϕ) and radiation within flat Friedman-Robertson-Walker (FRW) geometry. We establish the cur- rent model using intermediate form of scale factor and calculate the analytic solution of inflaton, effective potential V (ϕ) necessary to inflate the universe and entropy density S under slow-roll limit. The further work in this paper is restricted to high dissipative regime, taking constant and variable dissipa- tive (Γ) and viscous coefficients (ξ). The evaluated exact solutions are the main source in developing the inflationary observable like scalar/tensor power spec- tra, scalar/tensor spectral indices, tensor to scalar ratio and running of scalar spectral index for our model. The model parameters as well as additional the- ory parameter λ are constrained to check the compatibility of RG with Planck 2018 data via R − ns and αs − ns trajectories. We conclude that RG along with modification of Chaplygin gas model can lead to significant changes in the early universe.Item Accelerating Expansion in Curved FLRW Space-Time for Interaction/Non-interacting DE-DM within Rastall Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Shahnila; CIIT/FA19-RMT-086/LHR; Dr. Rabia Saleem; LHR TP 7446In this thesis, we explore the phenomenon of cosmic evolution using curved FLRW space-time bounded by apparent horizon with a specific holographic cut-off. To this end, we use the framework of Rastall gravity and universe is assumed to be consists of interacting/non-interacting dark energy and dark matter. In both scenarios, we evaluate exact solutions of the dynamical equa- tions and constraint the holographic parameter c2(z), assuming a slowly vary- ing function of red-shift during non-interacting model. For interacting model, we consider c2 as a constant function of red-shift. Moreover, we analyze nature of the obtained results via deceleration parameter (q), statefinder pair (j, s) and Om(z)-diagnostic by constraining the involved model parameters using latest observational data. The graphical analysis showed that interacting model is very close to ΛCDM model as compared to non-interacting case. We conclude that this holographic proposal is enough to describe the cosmic evolution at an accelerating rate.Item Inflationary and Accelerating Cosmic Solutions in Rastall Gravity(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Muhammad Waheed Zafar; SP19-RMT-011; LHR TP 6471; Dr. Rabia SaleemThe main focus of this thesis is to investigate accelerating expansion of our universe in the framework of Rastall theory of gravity (RTG) using non-linear inhomogeneousequationofstate(EoS)forFriedmann-Robertson-Walker(FRW) model. First we findthesolution of Hubble parameter, energy density and scale factor investigating the transition from non-phantom to phantom era. We study transition towards superaccelerating phase, i.e., the case when third derivative of the scale factor is positive. We find present and future singularity for our model. Second to check the thermodynamical evolution of cosmos, we find the product of temperature and entropy (TdS), and observe it graphically. To check the nature of cosmos, we find some important cosmological parameters using obtained solutions including deceleration, jerk, variable jerk, gradually varying jerk and snap parameters. Through detailed graphical analysis, we found that RTGis a good candidate to represent accelerating cosmic expansion.