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Subenoy Chakraborty

Publications and source records attributed to Subenoy Chakraborty.

At least 55 records · Page 3Linked to original sources
arXiv2023

Noether Symmetry analysis in Chameleon Field Cosmology

This work deals with chameleon field cosmology (a scalar field nonminimally coupled to cold dark matter) in the background of flat Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time. Both classical and quantum cosmology have been investigated using Noether symmetry analysis of the underlying physical system. The Wheeler-DeWitt (WD) equation has been constructed on the minisuperspace and solutions have been obtained using conserved charge.

gr-qc↗
arXiv2023

The Raychaudhuri Equation in inhomogeneous FLRW space-time : A $f(R)$-gravity model

In general description of the Raychaudhuri equation it is found that this first order non-linear differential equation can be written as a second order linear differential equation in the form of Harmonic Oscillator with varying frequency. Further, the integrability of the Raychaudhuri equation has been studied and also the expansion scalar is obtained in an explicit form. Subsequently, $f(R)$ gravity theory has been studied in the background of inhomogeneous FLRW spacetime with an aim to formulate the Raychaudhuri Equation. A congruence of time-like geodesics has been investigated using the Raychaudhuri Equation to examine whether the geodesics converge or not and some possible conditions are determined to avoid singularity. Finally, a brief quantum description has been presented.

gr-qc↗
arXiv2023

Multiscalar field cosmological model and possible solutions using Noether symmetry approach

In this work, a cosmological model is considered having two scalar fields minimally coupled to gravity with a mixed kinetic term. The model is characterized by the coupling function and the potential function which are assumed to depend on one of the scalar fields. Instead of choosing these functions phenomenologically here, they are evaluated assuming the existence of Noether symmetry. By appropriate choice of a point transformation in the augmented space, one of the variables in the Lagrangian becomes cyclic and the evolution equations become much simpler to have solutions. Finally, the solutions are analyzed from cosmological view point.

gr-qc↗
arXiv2023

Does diffusion mechanism favor the emergent scenario of the universe?

In the present work, the flat FLRW Universe has been modelled with cosmic matter in the form of diffusive barotropic fluid. The diffusive fluid undergoes dissipation due to diffusion mechanism in the form of cosmological scalar field. From the perspective of non-equilibrium thermodynamics, the evolution equations of the universe have been formulated. By a suitable choice of the cosmological scalar field, emergent scenario of the universe has been obtained.

gr-qc↗
arXiv2022

Does violation of Cosmic No-hair Conjecture guarantee the existence of Wormhole?

The present work investigates the interrelation between the validity (or violation) of the cosmic no-hair conjecture and the existence (or non-existence) of wormholes, both in Einstein's Gravity and in modified gravity theories. It is found that the existence of wormholes implies a violation of the cosmic no-hair conjecture, and the validity of the cosmic no-hair conjecture implies the non-existence of wormholes but not the reverse way both in Einstein's Gravity and in modified gravity theories. We will also re-visit the gravitational entropy predictions of the wormhole and show how they are connected.

gr-qc↗
arXiv2022

Analytic Solutions and Observational support: A study of $f(R,T)$ gravity with $f(R,T)=R+h(T)$

The present work deals with cosmological solutions in $f(R,T)$ gravity theory for perfect fluid with constant equation of state ($ω$). For a viable cosmological solution $ω$ is restricted to $ω<\dfrac{1}{3}$. Also depending on the sign of an arbitrary constant one has two possible solutions: a finite universe model and an ever expanding model of the universe. Field theoretic description of the model and possibility of a ghost scalar field has been studied. Also, an equivalence with modified Chaplygin gas has been shown. Finally, from the observational data it has been concluded that this model represents an evolution of the universe from matter dominated phase to present accelerating phase.

gr-qc↗
arXiv2022

The role of closed timelike curves in particle motion within Van Stockum space-time: A generalization

The present work analyses the particle motion in the Van Stockum space-time considering the existence of closed timelike curves. Test particles with or without angular momentum are studied in the present geometry. It is found that only non-zero angular momentum test particles exist in the neighborhood of closed timelike curves. The minimum particle energy and the range of backward time jump in closed timelike geodesics are studied within a Cauchy horizon. Finally, a general prescription for CTC and CTG has been presented with appropriate examples.

gr-qc↗
arXiv2021

Is warm inflation quasi-stable?

The present work deals with a non-equilibrium thermodynamics that is associated with the scenario of warm inflation. The premise is that an adiabatic radiation production process holds exactly i.e. the radiation dilution is exactly counterbalanced by a dissipation term. Under this hypothesis, it is found that radiation particle number, temperature, radiation energy density and pressure are all conserved -- a contradiction to the very nature of the warm inflation dynamics. However, such exact adiabatic radiation production process never happens in any realistic analysis of warm inflation. In the slow roll approximation this holds at best at the zeroth order. Finally it is shown that a variable cosmological constant may accommodate the quasi-stable process in warm inflation with non-equilibrium thermodynamic description.

gr-qc↗
arXiv2021

Some specific wormhole solutions in $f(R)$-modified gravity theory

The paper deals with the static spherically symmetric wormhole solutions in $f(R)$-modified gravity theory with anisotropic matter field and for some particular choices for the shape functions. The present work may be considered as an extension of the general formalism in \cite{r15} for finding wormhole solutions. For isotropic matter distribution it has been shown that wormhole solutions are possible for zero tidal force and it modifies the claim in \cite{r17}. Finally energy conditions are examined and it is found that all energy conditions are satisfied in a particular domain with a particular choice of the shape function.

gr-qc↗
arXiv2021

Quantum cosmology with symmetry analysis for quintom dark energy model

Quantum cosmology with quintom dark energy model has been investigated in the present work using symmetry analysis of the underlying physical system. In the background of the flat FLRW model quintom cosmological model has been studied using Noether symmetry and appropriate conserved charge is obtained. The Wheeler-DeWitt (WD) equation is constructed on the minisuperspace and solutions are obtained using conserved charge.

physics.gen-ph↗
arXiv2021

Dynamical System Analysis of a Dirac-Born-Infeld Model : A Center Manifold Perspective

In this paper we present the cosmological dynamics of a perfect fluid and the Dark Energy (DE) component of the Universe, where our model of the dark energy is the string-theoritic Dirac-Born-Infeld (DBI) model. We assume that the potential of the scalar field and the warp factor of the warped throat region of the compact space in the extra dimension for the DBI model are both exponential in nature. In the background of spatially flat Friedman-Robertson-Walker-Lemaitre Universe, the Einstein field equations for the DBI dark energy reduce to a system of autonomous dynamical system. We then perform a dynamical system analysis for this system. Our analysis is motivated by the invariant manifold approach of the mathematical dynamics. In this method, it is possible to reach a definite conclusion even when the critical points of a dynamical system are non-hyperbolic in nature. Since we find the complete set of critical points for this system, the center manifold analysis ensures that our investigation of this model leaves no stone unturned. We find some interesting results such as that for some critical points there are situations where scaling solutions exist. Finally we present various topologically different phase planes and stability diagrams and discuss the corresponding cosmological scenario.

gr-qc↗
arXiv2021

Collapse Geometry in Inhomogeneous FRW model

Collapsing process is studied in special type of inhomogeneous spherically symmetric space-time model (known as IFRW model), having no time-like Killing vector field. The matter field for collapse dynamics is considered to be perfect fluid with anisotropic pressure. The main issue of the present investigation is to examine whether the end state of the collapse to be a naked singularity or a black hole. Finally, null geodesics is studied near the singularity.

gr-qc↗
arXiv2020

A Dynamical System Analysis of cosmic evolution with coupled phantom dark energy with dark matter

The present work is an example of the application of the dynamical system analysis in the context of cosmology. Here cosmic evolution is considered in the background of homogeneous and isotropic flat Friedmann-Lemaître-Robertson-Walker space-time with interacting dark energy and varying mass dark matter as the matter content. The Dark Energy (DE) is chosen as phantom scalar field with self-interacting potential while the Dark Matter (DM) is in the form of dust. The potential of the scalar field and the mass function of dark matter are chosen as exponential or power-law form or in their product form. Using suitable dimensionless variables the Einstein field equations and the conservation equations constitute an autonomous system. The stability of the non-hyperbolic critical points are analyzed by using center manifold theory. Finally, cosmological phase transitions have been detected through bifurcation analysis which has been done by Poincaré index theory.

gr-qc↗
arXiv2020

Does emergent scenario in Hořava-Lifshitz Gravity demand a ghost field?

The non-singular model of the Universe i.e. emergent scenario is now very well known in cosmology. In Einstein gravity such type of singularity free solution is possible in the context of non-equilibrium thermodynamical prescription (both in first and 2nd order theory) with particle creation mechanism. Also there are various models of emergent scenario in different gravity theories. The present work is a twofold attempt namely (i) it has been examined whether it is possible to have singularity free solution in Hořava-Lifshitz modified gravity theory, (ii) if such singularity free solution exists then whether such solution is thermodynamically viable. It is found that perfect fluid matter distribution with phantom nature can generate such type of solution for closed and flat model. Finally thermodynamical analysis has been studied both at the apparent horizon and at any arbitrary horizon.

gr-qc↗
arXiv2020

Homogeneous and Isotropic space-time, Modified torsion field and Complete cosmic scenario

The paper deals with cosmological solutions describing different phases of the Universe for the homogeneous and isotropic FLRW model of the Universe with torsion. Normally, torsion field is not suitable for maximally symmetric space time model. However, one may use a specific profile of vectorial torsion field, derived from a scalar function. By proper choices of the torsion scalar function, it is shown that a continuous cosmic evolution starting from the emergent scenario to the present late time acceleration is possible. Also thermodynamics of the system is analyzed and equivalence with Einstein gravity is discussed.

gr-qc↗
arXiv2020

Cosmic evolution in f(T) gravity theory

The paper deals with cosmology in modified f(T) gravity theory. With some phenomenological choices for the function f(T) it is possible to have cosmological solutions describing different phases of the evolution of the Universe for the homogeneous and isotropic FLRW model. By proper choice of the parameters involved in the function $f(T)$ and also in the cosmological solutions it is shown that a continuous cosmic evolution starting from the emergent scenario to the present late time acceleration is possible. Finally thermodynamical analysis of f(T) gravity is presented.

gr-qc↗
arXiv2020

Reconciling $H_0$ tension in a six parameter space?

Consistent observations indicate that some of the important cosmological parameters measured through the local observations are in huge tension with their measurements from the global observations (within the minimal $Λ$CDM cosmology). The tensions in those cosmological parameters have been found to be either weakened or reconciled with the introduction of new degrees of freedom that effectively increases the underlying parameter space compared to the minimal $Λ$CDM cosmology. It might be interesting to investigate the above tensions within the context of an emergent dark energy scenario proposed recently by Li and Shafieloo~\cite{Li:2019yem}. We find that the tension on $H_0$ is clearly alleviated within 68\% confidence level with an improvement of the $χ^2$ for CMB, for the above emergent dark energy model having only six free parameters similar to the spatially flat $Λ$CDM model. The tension on $H_0$ is still alleviated for every combined datasets considered in the work, however, such alleviation occurs by worsening the $χ^2$ compared to the $χ^2$ for $Λ$CDM model obtained for the same combined dataset.

astro-ph.CO↗