arXiv subjects

Rita Rani

Publications and source records attributed to Rita Rani.

6 recordsLinked to original sources

arXiv2026

Scale-Invariant Bounce Cosmology in Weyl f(Q) Gravity with Quintom Signature

We investigate a bouncing cosmological model within the Weyl-type $f(Q)$ gravity framework, employing a power-law form of the non-metricity scalar $Q$. The model successfully resolves the initial singularity problem by demonstrating a nonsingular bounce, where the universe transitions from a contracting phase $ \dot{a}(t)<0 $ to an expanding phase ($ \dot{a}(t)>0 $) at the bouncing point $t \approx 0.$ Key features include the violation of the null energy condition (NEC) near the bounce and the crossing of the phantom divide line ($ω=-1$) by the equation of state (EoS) parameter, indicating quintom-like behavior. The model exhibits accelerated expansion post-bounce, suggesting an inflationary phase. Stability analysis via the adiabatic index reveals instability near the bouncing point, while energy conditions highlight the dominance of dark energy. Additionally, the study explores scalar fields, showing that quintessence-like kinetic energy becomes negative and phantom-like kinetic energy peaks positively near the bounce, aligning with dark energy dynamics. The Hubble parameter, deceleration parameter, and Hubble radius further validate the bouncing scenario, with the latter displaying symmetric behaviour around the bounce. These results underscore the viability of Weyl-type $f(Q)$ gravity as a framework for nonsingular bouncing cosmologies, offering insights into early universe dynamics and dark energy behaviour.

gr-qc↗

arXiv2024

Power law cosmology in Gauss-Bonnet gravity with pragmatic analysis

In this study, we present an approach $ f(R, G) $ gravity incorporating power law in $ G $. To study the cosmic evolution of the universe given by the reconstruction of the Hubble parameter given by $ E(z) = \bigg( 1+\frac{z(α+(1+z)^β)}{2 β+ 1} \bigg)^{\frac{3}{2 β}} $. Subsequently, we use various recent observational datasets of OHD, Pantheon, and BAO to estimate the model parameters $ H_0,~α$, and $ β$ applying the Markov Chain Monte Carlo (MCMC) technique in the emcee package to establish the validity of the model. In our findings, we observe that our model shows consistency with standard $ Λ$CDM, transits from deceleration to acceleration, and enters the quintessence region in late times. The cosmological model satisfies necessary energy constraints, simultaneously violating the strong energy condition (SEC), indicating a repulsive nature and consistent with accelerated expansion. The cosmic evolution of the Hawking temperature and the total entropy for the various observational datasets also show the validity of the model. Thus, our established model demonstrates sufficient potential for explicitly describing cosmological models.

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arXiv2023

An FLRW accelerating universe model in Weyl type $f(Q)$ gravity and Observational Constraints

We propose to develop a cosmological model of the universe based on Weyl type $ f(Q) $ gravity which shows the transition from decelerating in the past to acceleration at present by considering a particular functional form of $ f(Q) $ gravity as $ f(Q) = ({H_0}^2) (α_1 + α_2 \hskip0.05in log ({H_0^{-2}} Q)) $. We have solved Weyl type $ f(Q) $ gravity field equations numerically and have obtained numerical solutions to the Hubble and deceleration parameters, distance modulus, and apparent magnitudes of stellar objects like SNIa Supernovae. We have also obtained numerical solutions for the Weyl vector $ w $, non-metricity scalar $ Q $, and the Lagrangian multiplier $ λ$ appearing in the action of $ f(Q) $ gravity. We have compared our theoretical solutions with the error bar plots of the Observed Hubble data set of $ 77 $ points, $ 580 $ distance modulus SNIa data set, and $ 1048 $ supernova Pantheon data sets of apparent magnitudes. It is found that our results fit well with the observed data set points. \bf{The model envisages a unique feature that although the universe is filled with perfect fluid as dust whose pressure is zero, still the weyl vector dominance f(Q) creates acceleration in it. }

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arXiv2023

An f(R,T) Gravity Based FLRW Model and Observational Constraints

We attempt to construct a Friedmann-Lemaitre-Robertson-Walker(FLRW) cosmological model in $f(R, T)$ gravity which exhibits a phase transition from deceleration to acceleration at present. We take $f(R,T) = R + 2 λT$, $λ$ being an arbitrary constant. In our model, the $λ$ parameter develops a negative pressure in the universe whose Equation of state is parameterized. The present values of model parameters such as density, Hubble, deceleration, Equation of state, and $λ$ are estimated statistically by using the Chi-Square test. For this, we have used three different types of observational data sets: the $46$ Hubble parameter data set, the SNeIa $715$ data sets of distance modulus, and the 66 Pantheon data set (the latest compilation of SNeIa 40 bined plus 26 high red shift apparent magnitude $m_b$ data set in the red shift ranges from $0.014 \leq z \leq 2.26 $). We have calculated the transitional red shift and time. The estimated results for the present values of various model parameters are found as per expectations and surveys. Interestingly, we get the present value of the density $ρ_0$, $\simeq 1.5 ρ_c $. The critical density is estimated as $ρ_c\simeq 1.88 ~ h_0^2~10^{-29}~gm/cm^3 $ in the literature. The higher value of the present density is attributed to the presence of some additional energies in the universe apart from baryon energy. We have examined the behavior of the pressure in our model. It is negative and produces acceleration in the universe. Its present value is obtained as $p_0 \simeq - 0.7 ρ_0$.

gr-qc↗

arXiv2022

Curvature dominance DE-model in $f(R)$-gravity

We have probed a cosmological model in $f(R)$-gravity, which is a cubic equation in scalar curvature $R$. The terms arise due to nonlinear $f(R)$ function are treated as energy due to curvature inspired geometry. As a result, we find accelerating expansion in the universe, which creates an anti-gravitating negative pressure in it. Some of the physical parameters are solved using numerical methods. The evolution of the model are examined by the latest observational Hubble data (46-data points) and Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leqslant z \leqslant1.62$). Some important features of the model have been discussed by analyzing the plots of various dynamical parameters. The plots of deceleration parameter $q$ and the Hubble parameter $H$ describe the accelerating expansion in the evolution of the Universe at the present epoch. The transition from deceleration to acceleration for our model is obtained at redshift $z_{tr} \simeq 0.694069$, which is in good agreement with $Λ$CDM. We have also carried out state finder analysis for our model. The analysis of specific features of the model confirms that our model is consistent with $Λ$CDM in late times.

gr-qc↗

arXiv2022

An Axially Symmetric Transitioning models with Observational Constraints

In this study, we have demonstrated the expansion history of an axially symmetric Bianchi type-I model of the universe. Our model as of now presents an accelerating universe, which had been in the decelerating phase in the past. Roles of the two crucial Hubble~$H(z)$ and deceleration~$q(z)$ parameters are examined. The energy parameters of the universe are estimated with the help of the latest observational Hubble data (46-data points) and Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leq z \leq 1.62)$. We also discuss the stability analysis of the model by state finder diagnosis. The analysis reveals that in late time, the model is a quintessence type and points towards the $Λ$CDM model. Our developed model agrees with observational findings in a proper way. We have discussed some of the physical aspects of the model.

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