Department of Mathematics

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Author: search.filters.author.Dr. Rabia SaleemSubject: search.filters.subject.MATHEMATICS

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    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 Saleem
    The 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.
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    Analysis of Light Rings and Accretion Disk around a Static Kalb-Ramond Black Hole
    (Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Afifa Naureen; SP23-RMT-002; Dr. Rabia Saleem; LHR TP 9749
    The gravitational impact causes light traveling close to the black hole (BH) to be deflected, creating a dark central region known as BH shadow, which is often surrounded by a lu minous ring. The shadow of BH are closely related to the model parameters as well as the nature of accretion disk. Our primary focus is on the visible and shadow characteris tics of non-commutative (NC) Kalb-Ramond BH, which is encircled by diverse accretion profiles.Specific values were chosen for the model parameters to produce the BH shadow profile, and we came to the conclusion that changes in each parameter directly affect the size and light paths of the BH. We determine that the profile of BH includes the bright pho ton ring with its direct lensing, emissions and the dark inner area for accretion disk. Their specifics are dependent on the emissions, though; in general, direct emission contributes significantly to the overall apparent luminosity, while photon and lensing rings contribute very little, as is customary, and latter can be safely disregarded.
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    Baryogenesis in f(R) Theory of Gravity
    (Library Information Services, COMSATS University Islamabad, Lahore Campus, 2025) Laiba Zulfiqar (FA20-BSM-018) : Adeeba Iqbal (FA20-BSM-063); Dr. Rabia Saleem; LHR TP 9926
    f (R) Theory of gravity are reviewed in the context of the so called gravitational baryoge nesis. The latter is a mechanism for generating the baryon asymmetry in the universe, and relies on the coupling between the Ricci scalar curvature R and the baryon current. Gravity Lagrangians of the form L(R) ∼ Rn, where n differs from 1 (the case of the General Rela tivity) only for tiny deviations of a few percent, are consistent with the current bounds on the observed baryon asymmetry.