arXiv subjects

Nilanjana Mahata

Publications and source records attributed to Nilanjana Mahata.

9 recordsLinked to original sources

arXiv2026

The peculiar case of the Viaggiu holographic dark energy

We study the plausibility of a holographic dark energy (HDE) model using the form of horizon entropy proposed by Viaggiu in 2014. This form of entropy is a generalization of the usual Bekenstein-Hawking entropy, having an extra term arising due to the dynamical nature of horizons in an expanding universe. We examine this new HDE model in the context of a flat Friedmann-Lemaître-Robertson-Walker universe filled with two cosmic fluids -- dark matter in the form of dust and holographic dark energy generated by Viaggiu entropy. We consider the Hubble horizon and the future event horizon as characteristic length scales and study the evolution of the Universe within these frameworks. Our analysis reveals some intriguing findings that include a possible cosmic doomsday scenario in the future, and certain observations are in striking contrast to other HDE models studied in the literature.

gr-qc↗

arXiv2025

Phase space analysis of Rényi Holographic dark energy model

Recent observational evidences point out towards a late time acceleration of the universe. In order to study the accelerated expansion, scientists have incorporated the existence of an exotic matter with negative pressure, termed as dark energy. Afterwards a new idea of dark energy have been studied depending on the holographic principle of quantum gravity, called as the Holographic Dark Energy(HDE). Later on modifying Bekestein-Hawking entropy, different generalized entropies have been proposed, one of them being Rényi entropy which leads to Rényi holographic dark energy model (RHDE). We have considered RHDE model with Hubble horizon as the IR cut off and have studied the cosmological behaviour under non interacting, linear and non-linear interacting scenarios with the help of dynamical systems analysis. We have also investigated the stability of the system around hyperbolic critical points along with the type of fluid description, evolution of equation of state parameter as well as matter and energy density parameters.

gr-qc↗

arXiv2025

For a flat Universe, $C_P/C_V=-q$ : another coincidence in Cosmology?

This paper deals with gravitational thermodynamics on the dynamical apparent horizon of an FLRW universe with dissipation. The dissipation is assumed to arise due to adiabatic gravitational particle creation. For the thermodynamic study, we consider the Bekenstein-Hawking formalism and also assume a nonzero curvature $κ$ for a general study. In particular, we study the unified first law, the generalized second law, and thermodynamic stability in our model. The specific heat capacities are taken into account for the study of thermodynamic stability. Our study reveals a nice result! The ratio of the specific heat capacity at constant pressure and that at constant volume in a flat FLRW universe with dissipation is nothing but the negative of the deceleration parameter. In classical thermodynamics, this ratio is known as the isentropic expansion factor or (for ideal gases) the adiabatic index. A more interesting fact that has come to light is that this relation is independent of the cosmological model used. So, this is actually a generic result in Big Bang Cosmology. We discuss the implications of this result on the evolution of the Universe. Finally, we determine the constraints on the effective equation of state and the particle creation rate which guarantees thermodynamic stability in our model.

gr-qc↗

arXiv2024

Cosmological implications of non-minimally coupled f(Q) gravity

We experience some challenges in general gravitational theory owing to Einstein to explain late time acceleration of universe. To address this issue, geometric components of gravity have been modified in quite a few occasions to have a more general structure with some freedom. One such approach is to change the geometric components of gravity where gravitational interaction is denoted by Q,Q being the non-metricity. In our work, we have considered symmetric teleparallel gravity i.e, modified the geometry with the help of non-metricity Q or f(Q) gravity. We have considered a specific form of f(Q) which is nothing but the linear combination of Q and αQ^{n}, n\neq 1, where Q is coupled with Lagrangian matter. Forming the autonomous system from governing equations and then solving it, we have tried to analyze the nature of universe using dynamical system analysis. We have studied the behavior of the universe under several circumstances. Then, we have studied the stability around critical points and considering the recent observational data available for some cosmological parameters, feasible solutions are noted which depict late time acceleration. We can see that f(Q) gravity model can be considered as an alternative model to λCDM model.

gr-qc↗

arXiv2015

A Dynamical System Analysis of Three Fluid cosmological Model

In Friedman-Robertson-Walker flat spacetime, we consider a three fluid cosmological model which contains dark matter, dark energy and baryonic matter in the form of perfect fluid with a barotropic equation of state. Dark matter is taken in form of dust and dark energy is described by a scalar field with a potential $V(ϕ)$. Einstein's field equations are reduced to an autonomous dynamical system by suitable redefinition of basic variables. Considering exponential potential for the scalar field, critical points are obtained for the autonomous system. Finally stability of the critical points and cosmological implications are analyzed.

gr-qc↗

arXiv2015

A Dynamical System Analysis of Holographic Dark Energy Models with Different IR Cutoff

The paper deals with a dynamical system analysis of the cosmological evolution of an holographic dark energy (HDE) model interacting with dark matter (DM) which is chosen in the form of dust. The infrared cut-off of the holographic model is chosen as future event horizon or Ricci length scale. The interaction term between dark energy and dark matter is chosen of following three types i) proportional to the sum of the energy densities of the two dark components ii) proportional to the product of the matter energy densities and iii) proportional to dark energy density. The dynamical equations are reduced to an autonomous system for the three cases and corresponding phase space is analyzed.

gr-qc↗

arXiv2015

Dynamical system analysis for DBI dark energy interacting with dark matter

A dynamical system analysis related to Dirac Born Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW space time, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

gr-qc↗

arXiv2014

Dynamical System Analysis for a phantom model

The paper deals with a dynamical system analysis related to phantom cosmological model . Here gravity is coupled to phantom scalar field having scalar coupling function and a potential. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables and assuming some suitable form of the potential function. Finally, critical points are evaluated, their nature have been analyzed and corresponding cosmological scenario has been discussed.

gr-qc↗

arXiv2013

Dilatonic Scalar Field: A Dynamical System Analysis

The work deals with homogeneous and isotropic, flat FRW model of the universe which is filled up with non-interacting dark matter and dark energy to compatible with recent observational evidences. By choosing the dark energy in the form of a dilatonic scalar field, the evolution equations are reduced to an autonomous system. A phase space analysis is done around the critical points and stability criteria is examined. Finally, cosmological implications of the nature of the critical points are discussed.

gr-qc↗