arXiv subjects

Aroonkumar Beesham

Publications and source records attributed to Aroonkumar Beesham.

At least 19 recordsLinked to original sources

arXiv2026

Compact objects in AdS spacetime with exponential, quadratic and power-law bosonic mass profiles

This paper reports a study on the formation and physical characteristics of compacts stars in AdS spacetime within the framework of Bose-Einstein Condensate. Considering a Bose-Einstein condensate background at zero temperature this study works on total mass, compactness, surface redshift, density, pressure, adiabatic index and energy conditions. The bosonic mass has been taken as three distinct functions of radial coordinate in exponential form, quadratic form, and power law form. Our results reveal that the mass increases monotonically with radius and remains within observational limit for all the observationally motivated compact-star mass scales considered in this study and the compactness for all the cases is within Buchdahl's limit and hence it was confirmed that the configuration correspondence to compact stellar configuration models rather than forming a collapsing model. Both NEC and SEC are satisfied throughout the stellar interior and hence dynamical stability is ensured. Furthermore, the study also confirms the enhanced mass concentration near the outer region in the stellar models under consideration. Hence present study explores the physical properties and stability of compact bosonic configurations in AdS spacetime within a holographically motivated framework. The present analysis is primarily phenomenological and qualitative in nature. The models considered here are intended to explore possible behaviours of self-gravitating bosonic configurations in AdS geometry and are not proposed as fully realistic neutron-star models.

gr-qc↗

arXiv2025

Dynamics of late time universe in $f(Q)$ gravity

We construct cosmological model in nonmetricity scalar functional gravitational Lagrangian $f(Q)$ which describes the dynamical evolution of the late accelerating universe. Cosmological models are constructed considering different functional of $f(Q)$ gravity where $Q$ in the gravitational action. We obtain cosmological model probing late universe with a constant jerk parameter. The observational constraints that are imposed on the model parameters for a realistic scenario estimated using the observational Hubble data and the Pantheon dataset. The evolution of the deceleration parameter, energy density and the equation of state (EoS) parameter are also explored. The transition of the universe from a deceleration to an accelerating phase is investigated in different framework of $f(Q)$ theories. We also analyzed the variation of the effective EoS parameter and found that the matter content in the universe favours quintessence type fluid in all the $f(Q)$-gravity. The energy conditions for a realistic scenario are examined and noted that the effective fluid violates the strong energy condition.

gr-qc↗

arXiv2025

Parametrization Framework for the Deceleration Parameter in Scalar Field Dark Energy Model

We propose a Friedmann-Lemaitre-Robertson-Walker cosmological model with a scalar field that represents dark energy. A new parametrization of the deceleration parameter is introduced of the form $q = 1 + \eta (1 + \mu a^{\eta})$ where $\eta$ and $\mu$ are model parameters. and the compatibility of the model is constrained by recent observational datasets, including cosmic chronometers, Pantheon+ and Baryon Acoustic Observations. By considering a variable deceleration parameter, we address the expansion history of the universe, providing a viable description of the transition from deceleration to acceleration. Using the Markov Chain Monte Carlo method, the parameters of the model are constrained and we examine the cosmological parameters. A comparison is then made with the $\Lambda$CDM model using the latest observations. We examine the history of the main cosmological parameters, such as the deceleration parameter, jerk parameter, snap parameter, density parameter, and equation-of-state parameter, by constraining and interpreting them to reveal insights into what has been dubbed "dynamical dark energy" under the assumptions made above. Our method provides a framework that is independent of the model to explore dark energy, leading to a deeper and more subtle understanding of the mechanisms driving late-time cosmic acceleration.

astro-ph.CO↗

arXiv2024

Observational Constraints on Model with specific q

We place observational constraints on an FLRW cosmological model in $f(R,L_m)$ gravity with a specific deceleration parameter that depends on the scale factor. This form of the deceleration parameter has been discussed by authors in several papers, but none of them have applied observations to constrain the variables of the model. We carry this out with the cosmic chronometer, supernovae and the baryon acoustic oscillation datasets. The optimum values for the relevant parameters are found and used to plot the kinematical and physical parameters of the model. Although the model tends to the standard Lambda cold dark matter model at late times, there are several issues with the model concerning the values of some of the parameters and the energy conditions. The transition redshift of the model does not match with Planck data. The equation of state parameter indicates that the model falls into the category of phantom dark energy, which is not well supported by observations. Thus, the model does not seem viable.

gr-qc↗

arXiv2024

Power law cosmology in modified theory with thermodynamics analysis

In this paper, we consider a cosmological model in $ f(R, G) $ gravity in a flat space-time, where $ R $ is the Ricci scalar and $ G $ is the Gauss-Bonnet invariant. The function $ f(R, G) $ is taken as a linear combination of $ R $ and an exponential function of $ G $. We analyze the observational constraints under a power law cosmology which depends on two physical parameters: the Hubble constant $ H_0 $ and the deceleration parameter $ q $. We constrain these two dependent parameters using the latest 77 points of the OHD data, 1048 points of the Pantheon data, and the joint data OHD+Pantheon and compare the results with the $ Λ$CDM. Also, we speculate constraints using a simulated data set for the future JDEM (Joint Dark Energy Mission)/Omega, supernovae survey. We see that $ H_0 $ is in very close agreement with some of the latest results from the Planck Collaboration that assume the $ Λ$CDM model. Our work in power law cosmology better fits the Pantheon data than the earlier analysis \cite{Kumar:2011sw, Rani:2014sia}. However, the constraints obtained on $ H $ average, $ $ and $ q $ average, $ $ using the simulated data set for the future JDEM/Omega, supernovae survey are found to be inconsistent with the values obtained from the OHD and the Pantheon data. Additionally, we discuss statefinder diagnostics and see that the power law models approach the standard $Λ$CDM model ($ q\rightarrow -1 $). This model satisfies the Generalized Second Law of Thermodynamics. Finally, we conclude that the power law cosmology in $ f(R, G) $ gravity explains most of the distinguished attributes of evolution in cosmology.

gr-qc↗

arXiv2024

Cross-correlation between the thermal Sunyaev-Zeldovich effect and the Integrated Sachs-Wolfe effect

We present a joint cosmological analysis of the power spectra measurement of the Planck Compton parameter and the integrated Sachs-Wolfe (ISW) maps. We detect the statistical correlation between the Planck Thermal Sunyaev-Zeldovich (tSZ) map and ISW data with a significance of a $3.6σ$ confidence level~(CL), with the autocorrelation of the Planck tSZ data being measured at a $25 σ$ CL. The joint auto- and cross-power spectra constrain the matter density to be $Ω_{\rm m}= 0.317^{+0.040}_{-0.031}$, the Hubble constant $H_{0}=66.5^{+2.0}_{-1.9}\,{\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$ and the rms matter density fluctuations to be $σ_{8}=0.730^{+0.040}_{-0.037}$ at the 68% CL. The derived large-scale structure $S_{8}$ parameter is $S_8 \equiv σ_{8}(Ω_{\rm m}/0.3)^{0.5} = 0.755\pm{0.060} $. If using only the diagonal blocks of covariance matrices, the Hubble constant becomes $H_{0}=69.7^{+2.0}_{-1.5}\,{\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$. In addition, we obtain the constraint of the product of the gas bias, gas temperature, and density as $b_{\rm gas} \left(T_{\rm e}/(0.1\,{\rm keV}) \right ) \left(\bar{n}_{\rm e}/1\,{\rm m}^{-3} \right) = 3.09^{+0.320}_{-0.380}$. We find that this constraint leads to an estimate on the electron temperature today as $T_{\rm e}=(2.40^{+0.250}_{-0.300}) \times 10^{6} \,{\rm K}$, consistent with the expected temperature of the warm-hot intergalactic medium. Our studies show that the ISW-tSZ cross-correlation is capable of probing the properties of the large-scale diffuse gas.

astro-ph.CO↗

arXiv2023

CoLFI: Cosmological Likelihood-free Inference with Neural Density Estimators

In previous works, we proposed to estimate cosmological parameters with the artificial neural network (ANN) and the mixture density network (MDN). In this work, we propose an improved method called the mixture neural network (MNN) to achieve parameter estimation by combining ANN and MDN, which can overcome shortcomings of the ANN and MDN methods. Besides, we propose sampling parameters in a hyper-ellipsoid for the generation of the training set, which makes the parameter estimation more efficient. A high-fidelity posterior distribution can be obtained using $\mathcal{O}(10^2)$ forward simulation samples. In addition, we develop a code-named CoLFI for parameter estimation, which incorporates the advantages of MNN, ANN, and MDN, and is suitable for any parameter estimation of complicated models in a wide range of scientific fields. CoLFI provides a more efficient way for parameter estimation, especially for cases where the likelihood function is intractable or cosmological models are complex and resource-consuming. It can learn the conditional probability density $p(\boldsymbolθ|\boldsymbol{d})$ using samples generated by models, and the posterior distribution $p(\boldsymbolθ|\boldsymbol{d}_0)$ can be obtained for a given observational data $\boldsymbol{d}_0$. We tested the MNN using power spectra of the cosmic microwave background and Type Ia supernovae and obtained almost the same result as the Markov Chain Monte Carlo method. The numerical difference only exists at the level of $\mathcal{O}(10^{-2}σ)$. The method can be extended to higher-dimensional data.

astro-ph.CO↗

arXiv2023

Quintessences Universe in $f(R, L_m)$ gravity with special form of deceleration parameter

In this paper We have investigated a homogeneous and isotropic FRW cosmological model with perfect fluid in the framework of $f(R,Lm)$ gravity. We have explored for the non linear case of $f(R,L_m)$ model, namely $f(R,L_m) = R/2 + L_m$ and obtained the solution by using the condition that the deceleration parameter is a linear function of the Hubble parameter. We employ 57 Hubble data points and 1048 Pantheon supernovae type Ia data samples to restrict the model parameters. Additionally, we employ Markoc Chain Monte Carlo (MCMC) simulation for our statistical analysis. Additionally, we analyse the jerk and om diagnostic parameters for our model using the parameter values that were obtained.

gr-qc↗

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↗

arXiv2023

A non-singular bouncing cosmology in $ f(R,T) $ gravity

We investigate a bounce realization in the framework of higher order curvature in $ f(R,T) $ modified theory of gravity. We perform a detailed analysis of the cosmological parameters to explain the contraction phase, the bounce phase, and the expansion phase. Furthermore, we observe a violation of the null energy condition, instability of the model, and a singularity upon deceleration at the bouncing point, which are the supporting results for a bouncing cosmology. The outcome of the slow roll parameters is satisfactory to understand the inflation era and the equation of state parameter exhibits a ghost condensate behavior of the model near the bounce. Additionally, we discuss the stability of the model using linear perturbations in the Hubble parameter as well as the energy density.

gr-qc↗

arXiv2023

Reconstruction of an Observationally Constrained $f(R, T)$ gravity model

In this paper, an attempt is made to construct a Friedmann-Lemaitre-Robertson-Walker model in $f(R,T)$ gravity with a perfect fluid that yields acceleration at late times. We take $f(R,T)$ as $R$ + $8πμT$. As in the $Λ$CDM model, we take the matter to consist of two components, viz., $Ω_m$ and $Ω_μ$ such that $Ω_m$ + $Ω_μ$=1. The parameter $Ω_m$ is the matter density (baryons + dark matter), and $Ω_μ$ is the density associated with the Ricci scalar $R$ and the trace $T$ of the energy momentum tensor, which we shall call dominant matter. We find that at present $Ω_μ$ is dominant over $Ω_m$, and that the two are in the ratio 3:1 to 3:2 according to the three data sets: (i) 77 Hubble OHD data set (ii) 580 SNIa supernova distance modulus data set and (iii) 66 pantheon SNIa data which include high red shift data in the range $0\leq z\leq 2.36$. We have also calculated the pressures and densities associated with the two matter densities, viz., $p_μ$, $ρ_μ$, $p_m$ and $ρ_m$, respectively. It is also found that at present, $ρ_μ$ is greater than $ρ_m$. The negative dominant matter pressure $p_μ$ creates acceleration in the universe. Our deceleration and snap parameters show a change from negative to positive, whereas the jerk parameter is always positive. This means that the universe is at present accelerating and in the past it was decelerating. State finder diagnostics indicate that our model is at present a dark energy quintessence model. The various other physical and geometric properties of the model are also discussed.

gr-qc↗

arXiv2023

The Reconstruction of Constant Jerk Parameter with $f(R,T)$ Gravity

In this work, we have developed an FLRW type model of a universe which displays transition from deceleration in the past to the acceleration at the present. For this, we have considered field equations of $f(R,T)$ gravity and have taken $f(R,T) = R + 2 λT$, $λ$ being an arbitrary constant. We have estimated the $λ$ parameter in such a way that the transition red shift is found similar in the deceleration parameter, pressure and the equation of state parameter $ω$. The present value of Hubble parameter is estimated on the basis of the three types of observational data set: latest compilation of $46$ Hubble data set, SNe Ia $580$ data sets of distance modulus and $66$ Pantheon data set of apparent magnitude which comprised of 40 SN Ia binned and 26 high redshift data's in the range $0.014 \leq z \leq 2.26 $. These data are compared with theoretical results through the $ χ^2 $ statistical test. Interestingly, the model satisfies all the three weak, strong and dominant energy conditions. The model fits well with observational findings. We have discussed some of the physical aspects of the model, in particular the age of the universe.

gr-qc↗

arXiv2022

Modeling Transit Dark Energy in $f(R, L_m)$-gravity

This research paper deals with a transit dark energy cosmological model in $f(R, L_{m})$-gravity with observational constraints. For this, we consider a flat FLRW space-time and have taken a cosmological cosntant-like parameter $β$ in our field equations. The model has two energy parameters~ $Ω_{m0}~ and~ Ω_{\beta0}$, which govern the mechanism of the universe, in particular its present accelerated phase. To make the model cope with the present observational scenario, we consider three types of observational data set: $46$ Hubble parameter data set, SNe Ia $715$ data sets of distance modulus and apparent magnitude, and $40$ datasets of SNe Ia Bined compilation in the redshift $0\leq z<1.7$. We have approximated the present values of the energy parameters by applying $R^{2}$ and $χ^{2}$-test in the observational and theoretical values of Hubble, distance modulus, and apparent magnitude parameters. Also, we have measured the approximate present values of cosmographic coefficients $\{H_{0}, q_{0}, j_{0}, s_{0}, l_{0}, m_{0}\}$. It is found that our approximated value-based model fits best with the observational module. We have found that as $t\to\infty$ (or $z\to 0$) then $\{q, j, s, l, m\}\to\{-1, 1, 1, 1, 1\}$. The cosmic age of the present universe is also approximated and comes up to the expectation. Our model shows a transit phase of the present accelerating universe with a deceleration in the past and has a transition point.

gr-qc↗

arXiv2021

Oscillation of cosmic space in the background of two interacting tachyonic BIons

When a brane-anti-brane system includes two tachyons, each of them produces a BIoninc wormhole. These wormholes interact with each other and form 4 regions. Two of the regions are related to the independent BIons which have been considered previously. However, two new regions correspond to the interacting BIons in which the cosmic parameters act oppositely to each other. We obtain the Hubble parameter and energy density of the universes in the new regions and show that by expanding a universe in one region, the universe in the other region contracts. Also, the evolution of the universes depend on the tachyonic fields, the separation between the branes and the size of the throats of the bionic wormholes.

hep-th↗

arXiv2021

Inflationary universe from anomaly-free $F(R)$-gravity

By adding a three dimensional manifold to an eleven dimensional manifold in supergravity, we obtain the action of $F(R)$-gravity and find that it is anomaly free. We calculate the scale factor of the inflationary universe in this model, and observe that it is related to the slow-roll parameters. The scalar-tensor ratio R\_(scalar-tensor) is in good agreement with experimental data.

hep-th↗

arXiv2021

LRS Bianchi I model with bulk viscosity in f(R,T) gravity

Locally-rotationally-symmetric Bianchi type-I viscous and non -viscous cosmological models are explored in general relativity (GR) and in f(R,T) gravity. Solutions are obtained by assuming that the expansion scalar is proportional to the shear scalar which yields a constant value for the deceleration parameter (q=2). Constraints are obtained by requiring the physical viability of the solutions. A comparison is made between the viscous and non-viscous models, and between the models in GR and in f(R,T) gravity. The metric potentials remain the same in GR and in f(R,T) gravity. Consequently, the geometrical behavior of the $f(R,T)$ gravity models remains the same as the models in GR. It is found that f(R,T) gravity or bulk viscosity does not affect the behavior of effective matter which acts as a stiff fluid in all models. The individual fluids have very rich behavior. In one of the viscous models, the matter either follows a semi-realistic EoS or exhibits a transition from stiff matter to phantom, depending on the values of the parameter. In another model, the matter describes radiation, dust, quintessence, phantom, and the cosmological constant for different values of the parameter. In general, f(R,T) gravity diminishes the effect of bulk viscosity.

gr-qc↗

arXiv2020

Quantum spectrum of tachyonic black holes in a brane-anti-brane system

Recently, some authors have considered the quantum spectrum of black holes . This consideration is extended to tachyonic black holes in a brane-anti-brane system. In this study, black holes are constructed from two branes which are connected by a tachyonic tube. As the branes come closer to each other, they evolve and make a transition to thermal black branes. It will be shown that the spectrum of these black holes depends on the tachonic potential and the separation distance between the branes. By decreasing the separation distance, more energy emerges and the spectrum of the black hole increases.

hep-th↗

arXiv2020

Plane symmetric model in $f(R,T)$ gravity

A plane symmetric Bianchi-I model is explored in $f(R,T)$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of energy-momentum tensor. The solutions are obtained with the consideration of a specific Hubble parameter which yields a constant deceleration parameter. The various evolutionary phases are identified under the constraints obtained for physically viable cosmological scenarios. Although a single (primary) matter source is taken, due to the coupling between matter and $f(R,T)$ gravity, an additional matter source appears, which mimics a perfect fluid or exotic matter. The solutions are also extended to the case of a scalar field model. The kinematical behavior of the model remains independent of $f(R,T)$ gravity. The physical behavior of the effective matter also remains the same as in general relativity. It is found that $f(R,T)$ gravity can be a good alternative to the hypothetical candidates of dark energy to describe the present accelerating expansion of the universe.

gr-qc↗