arXiv subjects

Prabir Rudra

Publications and source records attributed to Prabir Rudra.

At least 19 recordsLinked to original sources

arXiv2026

Evolving wormhole cosmology: modified Friedmann dynamics and observational constraints

We construct an evolving wormhole cosmological model from a Morris--Thorne metric with a separable, time-dependent shape function in a spatially flat Friedmann--Lemaitre--Robertson--Walker background, deriving the corrected wormhole energy-momentum tensor and a volume-averaging procedure that yields a modified Friedmann equation with a redshift-dependent wormhole correction term. We show that the shape-function index and throat-evolution exponent combine into a single macroscopic exponent $β$, and we demonstrate that the resulting wormhole equation of state is consistent with this geometric averaging. All traversability conditions are verified. Confronting the model with cosmic chronometer, DESI Data Release~2 BAO, and standard BAO data across seven dataset combinations, our findings show that all combinations are mutually consistent, with the joint fit giving a present-day expansion rate intermediate between local and CMB-inferred values, a deceleration-to-acceleration transition consistent with independent determinations, and an effective dark-energy equation of state close to, but distinguishable from, a pure cosmological constant. The evolving throat radius offers a novel, geometry-specific observable for discriminating wormhole spacetimes from phenomenological dark-energy parametrisations.

gr-qc↗

arXiv2026

Interplay of Holographic and New Agegraphic Dark Energy in Cosmology: A hybrid dark energy model from a generalized length-time cut-off

The spatial and temporal infrared cutoffs are the source of the Holographic dark energy (HDE) and New Agegraphic dark energy (NADE) models, respectively. Inspired by the spacetime unification of space and time in General Relativity, we propose that a combined spacetime cutoff should govern the dark energy density, with HDE and NADE appearing as limiting cases when the spatial or temporal contribution predominates. In this connection, we explore a hybrid model of holographic and new Agegraphic dark energy, where the energy density of the resulting model is a combination of the two models. We consider an interacting and a non-interacting scenario between the hybrid dark energy model and cold dark matter. Cosmological implications of the model is studied via different cosmological parameters like the equation of state parameter, deceleration parameter, statefinder parameter, and Om-diagnostic. A stability check for the model has been performed using the squared speed of sound. Finally the parameter space of the model is constrained using observational data like Hubble data, BAO data and DESI data. We have also checked the Hubble tension for our hybrid model and found it to be substantially low in comparison to other models. From our analysis we see that the constructed hybrid dark energy model can describe the evolution of the universe successfully.

gr-qc↗

arXiv2026

Ricci-Cubic Holographic Dark Energy: Confronting Observations, Stability and the Cosmic Coincidence Problem

In this work, we constrain the parameter space of the Ricci-Cubic Holographic Dark Energy (RCHDE) model using several observational datasets, including Hubble parameter measurements, cosmic chronometer (CC) data, Baryon Acoustic Oscillation (BAO) data, and recent DESI observations. The RCHDE model is constructed from a cubic curvature invariant formed through cubic contractions of the Ricci and Riemann tensors. To estimate the model parameters, we employ the Markov Chain Monte Carlo (MCMC) sampling technique within a Bayesian inference framework. The resulting likelihood contours provide both marginalized and joint posterior distributions of the model parameters. The best-fit cosmological evolution predicted by the RCHDE model is reconstructed and compared with observational $H(z)$ measurements as well as with the standard $Λ$CDM cosmological model. The best-fit value obtained in our model exhibits a moderate Hubble tension of approximately $2.3σ$ with respect to the reference value for $Λ$CDM. While this indicates a noticeable discrepancy, it remains significantly lower than the $\sim 5σ$ tension typically reported between early- and late-Universe measurements, suggesting a partial alleviation of the tension. In addition to the statistical parameter estimation, we perform an enhanced machine learning analysis using observational Hubble parameter data. We have done a comparative stability analysis between different holographic dark energy models using the squared speed of sound, where it is seen that the RCHDE model does not have any upper hand over its counterparts. Finally, the cosmic coincidence problem is tested to compare the efficiency of the RCHDE model in comparison to other models. It is found that the RCHDE model produced a significant alleviation to the cosmic coincidence problem, outshining its counterparts.

astro-ph.CO↗

arXiv2026

Warm Inflation in $f(Q)$ gravity

We investigate warm inflation in the framework of $f(Q)$ gravity within a Friedmann-Robertson-Walker spacetime. Unlike cold inflation, where the inflaton evolves in isolation, warm inflation features continuous interaction between the inflaton field and radiation throughout the inflationary epoch, facilitating energy transfer through dissipative processes and maintaining thermal equilibrium. In our novel approach, we employ $f(Q)$ dark energy as the driving mechanism for warm inflation, leveraging the geometric degrees of freedom associated with non-metricity as dynamical variables. We derive the field equations using slow-roll approximations and analyze two specific $f(Q)$ models: a power-law form $f(Q) = Q + m Q^n$ and a logarithmic form $f(Q) = mQ\ln(nQ)$. Our analysis focuses on the high-dissipative regime, where thermal fluctuations dominate over quantum fluctuations. We compute key inflationary observables, including the scalar spectral index $n_s$, tensor-to-scalar ratio $r$, and slow-roll parameters. Our results demonstrate that $f(Q)$ dark energy successfully drives warm inflation while satisfying essential physical conditions: initial dominance of $f(Q)$ energy density over radiation density initially, and thermal fluctuations exceeding quantum fluctuations ($T > H$). As inflation progresses, energy transfers from the geometric $f(Q)$ sector to radiation, eventually bringing both densities to comparable levels near inflation's end. Importantly, our computed values align well with current observational constraints from Planck and BICEP/Keck: $n_s = 0.965 \pm 0.004$ and $r < 0.036$. This validates the viability of warm inflation in $f(Q)$ gravity and establishes a unified geometric framework for understanding both early universe inflation and late-time cosmic acceleration.

gr-qc↗

arXiv2025

Some New Types of Well-Behaved Polynomial Redshift Parametrization of Dark Energy Equation of State

In this paper, we explore a new type of smooth and well-behaved polynomial redshift function that can avoid a future singularity. Using this function, we have proposed different redshift parametrizations of the dark energy equation of state, drawing motivation from different polynomial functions like conventional polynomial, Legendre polynomial, Laguerre polynomial, Chebyshev polynomial and Fibonacci polynomial. The main feature of these parametrizations is their well-behaved nature throughout the evolution of the universe, which was a matter of concern in most of the previous polynomial parametrizations of the dark energy equation of state (EoS). This form of parametrization may be considered as an extension of those forms with no divergence at any redshift value. A comprehensive observational data analysis is performed with the Hubble, BAO and DESI datasets to constrain the parameter space of the models. Confidence contours showing joint and marginalized posterior distribution with different combinations of datasets are generated using a Markov Chain Monte Carlo approach. We see that our improved parametrizations enable us to derive more stringent restrictions on the current dark energy EoS and its derivative, which improves performance. Finally, a machine learning analysis is performed using some suitable algorithms like ELR, PILR, ANN, SVR, ERFR and GBR to compare the models. Among all the tested polynomial bases, the Legendre basis demonstrated superior performance with the lowest test RMSE and reduced $χ^{2}$ value under the Modified Differential Evolution theoretical model, indicating exceptional physical accuracy and numerical stability.

gr-qc↗

arXiv2025

Godel Universe in $f(Q,T)$ gravity: Exploring causality violation and closed time-like curves

In this work, the classical Godel solution from general relativity is extended into the framework of modified gravity theories based on non-metricity $Q$ and the trace of the energy-momentum tensor $T$ in the context of $f(Q,T)$ gravity. The main feature of the Godel solution is the existence of closed time-like curves, which allow for causality violation and time travel. Since general relativity and its extensions do not demand spacetime to be globally causal, there is good motivation to explore such solutions. We have found classes of solutions with different matter content, like perfect fluid, cosmological constant, massless scalar field, etc. It is observed that, for suitable initial conditions, there is always a possibility of obtaining feasible solutions that violate causality in our setup. The presence of non-metricity in such solutions produces crucial deviations that are noteworthy.

gr-qc↗

arXiv2025

Study of Wormhole in $f(Q)$ gravity with some dark energy models

This study discusses the development of some particular static wormhole models in the background of an extended $f(Q)$ gravity theory. Wormhole solutions are derived by considering the radial pressure to admit an equation of state corresponding to Chaplygin gas. The Chaplygin gas equation of state is taken into consideration in two different forms: $p_{r}=-\frac{Bb(r)^{u}}{ρ^{a}}$, $p_{r}=-\frac{B}{ρ^{a}}$. Wormhole models are also generated assuming that a variable barotropic fluid may explain the radial pressure given by $p_{r} =-ωρb(r)^u$. For every model, the shape function $b(r)$ is the function that can be derived from the wormhole metric in any scenario. The stability analysis of the wormhole solutions and the shape function viability for each situation are then investigated.Since each wormhole model is shown to violate the null energy condition (NEC), it can be understood that these wormholes are traversable. More generally, we investigate whether the model is stable under the hydrostatic equilibrium state condition using the TOV equation.The physical characteristics of these models are shown under the same energy circumstances. The typical characteristic is the radial pressure $p_{r}$ near the wormhole throat, which violates the NEC $(ρ+P_{r} \geq0)$. In some models, it is possible to meet the NEC at the neck and yet violate the DEC $(ρ- P_{r}\geq0)$. In summary, precise wormhole models may be generated, provided that $(ρ\geq0)$, and there may be a potential breach of the NEC at the wormhole's throat.

gr-qc↗

arXiv2025

Warm Inflation with Barrow Holographic Dark Energy

In this work, we study the warm inflation mechanism in the presence of the Barrow holographic dark energy model. Warm inflation differs from other forms of inflation primarily in that it assumes that radiation and inflaton fields exist and interact throughout the inflationary process. After the warming process, energy moves from the inflaton to the radiation as a result of the interaction, keeping the cosmos warm. Here we have set up the warm inflationary mechanism using Barrow holographic dark energy as the driving agent. Warm inflation has been explored in a highly dissipative regime, and interesting results have been obtained. It is seen that the Barrow holographic dark energy can successfully drive a warm inflationary scenario in the early universe. Finally, the model was compared with the observational data, and compliance was found.

gr-qc↗

arXiv2025

A Cosmological Holographic Reconstruction of f(Q) Theory

This paper explores a cosmological reconstruction scheme in the background of f(Q) gravity theory from a Holographic perspective. The basic motivation for this work is that the reconstruction is performed from a holographic origin, which has its roots in the black hole thermodynamics and quantum gravity. Dark energy models inspired by holographic prescription are used to reconstruct the f(Q) gravity models. Two such models, namely the Granda-Oliveros holographic dark energy model and its generalization, the Chen- Jing model are considered for the study. Different scale factors are used and a thorough reconstruction scheme is set up using the dark energy models. The observationally constrained values of the free model parameters have been used to form the reconstructed models. Finally, a thorough investigation of the energy conditions has been performed to check the cosmological viability of the reconstructed f(Q) models. As an outcome, we get some very promising and cosmologically viable f(Q) models that present some interesting properties and demand further investigation.

gr-qc↗

arXiv2024

Gravitational waves driven by Holographic dark energy

In this paper, we have studied the effects of holographic dark energy on the evolution of gravitational waves. The background evolution of gravitational waves in a flat FRW universe is considered and studied in the presence of various holographic dark energy models. The perturbation equations governing the evolution of the gravitational waves have been constructed and solutions are obtained. These solutions are studied in detail to get a proper understanding of the characteristics of the gravitational waves in the presence of holographic dark energy. The work can be a significant tool in studying different dark energy models comparatively using the features of the gravitational wave evolution.

gr-qc↗

arXiv2024

Gravitational Collapse of Bose-Einstein condensate dark matter in Generalized Vaidya spacetime

In this work, we study the gravitational collapse procedure in generalized Vaidya spacetime with Bose-Einstein condensate dark matter density profile. We use the generalized Vaidya metric to simulate the spacetime of a big star and subsequently obtain the field equations. Then we proceed to determine the star system's mass parameter by solving the field equations. Then the gravitational collapse mechanism is investigated using the derived solutions. Investigating the nature of the singularity (if formed) as the end state of the collapse is the main goal. Dark matter in the form of Bose-Einstein condensate is expected to play a crucial role in the fate of the collapse. We see that there is a possibility of the formation of both black holes and naked singularities as the end state of the collapse depending upon the initial conditions. The junction conditions are derived with a Vaidya exterior and a Friedmann interior and some important insights are obtained. A Penrose diagram showing the causal relations between the spacetimes is generated and studied in detail.

gr-qc↗

arXiv2024

Relativistic model of anisotropic star with Bose-Einstein density depiction in $f(T)$ gravity

This article presents a new model for anisotropic compact stars that are confined to physical dark matter in the background of $f(T)$ teleparallel gravity. The model is based on the equation of state (EoS) of the bag model type and the Bose-Einstein dark matter density profile. The derived solutions meet the energy conditions, the causality conditions, and the required conditions on the stability factor and adiabatic index, indicating that they are physically well-behaved and represent the physical and stable matter configuration. We also determine the maximum mass, surface redshift, and compactness parameter at the surface. Interestingly, all of these numbers fall within the specified range, supporting the physical viability of our proposal. Additionally, the various masses that are derived for varying the model parameter $k$ correspond to five compact, realistic compact objects, including LMC X-4, Her X-1, 4U 1538-52, SAX J1808.4-3658, and Cen X-3. We have also illustrated the radially symmetric profiles of energy density and the moment of inertia for non-rotating stars.

gr-qc↗

arXiv2024

A new type of $f(\mathcal{T})$ gravity from Barrow entropy

In this work, two originally separate adjustments for the Friedmann equations are concurrently considered. Firstly, the fractal structure of the black hole horizon region is imposed by the Barrow entropy. The second adjustment is the $f(\mathcal{T})$ gravity, which is based on a teleparallel framework generalization of the Einstein-Hilbert action, where $\mathcal{T}$ is the scalar torsion. This can be considered as a Barrow entropy modification of the $f(\mathcal{T})$ gravity thus yielding a new model. Gravity thermodynamics hypothesis principles are used to integrate these two models under a unified framework. We derive the modified Friedmann equation and note the corrections obtained. To understand the implications of such dual modifications, an application is analyzed and a particular $f(\mathcal{T})$ toy model is chosen for the purpose. The equation of the state parameter of the resulting model, the dimensionless density parameters of matter and dark energy, and the deceleration parameter are explored to check the viability of the new model. A discussion of the dynamic evolution of the universe follows from these results. It is seen that the results comply with the observations. The newly developed model is promising and demands further study.

gr-qc↗

arXiv2024

The effects of the pole dark energy on gravitational waves

In this paper, we have studied the effects of pole dark energy on the evolution of gravitational waves. The background evolution of gravitational waves in a flat FRW universe is considered and its dynamics are studied in the presence of pole dark energy. Two different potential functions are considered for the study. Using the field equations, we formulated the perturbed equations governing the evolution of gravitational waves with respect to redshift z within the background of the FRW Universe. Subsequently, we delved into the characteristics of gravitational waves for the pole dark energy model and reached interesting results.

gr-qc↗

arXiv2024

Gravitational Collapse in Energy-momentum squared gravity: Nature of singularities

In this paper, we explore a collapsing scenario in the background of energy-momentum squared gravity (EMSG). EMSG claims to have terms that originate from the quantum gravity effects mimicking loop quantum gravity. As a result, the framework admits a bounce at a finite time thus avoiding a singularity. So the question that naturally arises: Is there any realistic chance of the formation of a black hole or the quantum gravity effects are strong enough to totally avoid such a pathology? Motivated by this we are interested in studying a gravitational collapse mechanism in the background of EMSG and investigate the fate of such a process. We model the spacetime of a massive star by the Vaidya metric and derive the field equations in EMSG. Then using the equations we go on to study a gravitational collapse mechanism, on two specific models of EMSG with different forms of curvature-matter coupling. The prime objective is to probe the nature of singularity (if formed) as the end state of the collapse. We see that none of the models generically admit the formation of black holes as the end state of collapse, but on the contrary, they support the formation of naked singularities. This can be attributed to the quantum fluctuations of the gravitational interactions at the fundamental level.

gr-qc↗

arXiv2024

Non-relativistic quantum particles interacting with pseudoharmonic-type potential under flux field in a topological defect geometry

In this work, we investigate the quantum motions of non-relativistic particles interacting with a potential in the presence of the Aharonov-Bohm (AB) flux field within a topological defect geometry, for example, space-time with a distortion of a vertical line into a vertical spiral. We begin by deriving the radial Schrödinger wave equation, incorporating an anharmonic oscillator potential, which is a superposition of a harmonic oscillator and an inverse square potential, along with a constant term. The eigenvalue solution is obtained through the confluent Heun equation focusing on the ground state energy level and the radial wave function for the radial mode $n=1$ as an example and analyze the results. Subsequently, we use these results in molecular potential models, considering pseudoharmonic and shifted pseudoharmonic potentials. The derived eigenvalue solutions provide insights into the behavior of particles within these potentials. Expanding our exploration, we study the quantum system featuring only an inverse square potential in the presence of the quantum flux field in the same geometry background. Employing the same procedure, we determine the ground state energy level and the radial wave function. Notably, our findings reveal that the eigenvalue solutions are significantly influenced by the topological defect characterized by the parameter $β$, and the quantum flux field $Φ_{AB}$. This influence manifests as a shift in the energy spectrum, drawing parallels to the gravitational analog of the Aharonov-Bohm effect.

quant-ph↗

arXiv2024

Unveiling the Fifth State of Matter: Insights into Ultra-Hot Plasma and its Applications

In this work, we investigate the dissociation energy of the North (N) and South (S) poles of a quantum magnetic particle, incorporated within both classical and quantum mechanical perspectives. A simple model of a harmonic oscillator is employed to estimate the dissociation energy of the N-S poles, as well as the corresponding breakdown temperature and internal pressure. The results indicate that the separation of magnetic poles occurs in two states: (a) in an ultra-hot plasma medium with extremely high temperatures, such as in the core of a hot star, and (b) at extremely high pressures, such as between internal plates in complex superlattices of layered solids. The breakdown temperature is found to be of the order of $10^7$ to $10^8$ Kelvin, which is only achievable in an ultra-hot plasma environment, known as the fifth phase of matter. Based on this model, the possibility of dissociation of bonds between N and S magnetic poles for solid superlattices under very high pressures between crystal plates is also calculated. The results suggest that the presence of isolated magnetic monopoles in superlattices of solids under ultra-high-pressure conditions is possible. Consequently, the model proposes that the conductivity of magnetic monopole carriers can be applied to the manipulation of nanomaterials for the production of advanced devices, such as new generations of superconductors, new spin devices, and magnetic-electronics, advanced materials with magnetic monopoles, as well as super-dielectrics.

physics.plasm-ph↗

arXiv2023

Reconstruction of $f(T,\mathcal{T})$ Lagrangian for various cosmological scenarios

In this paper, we explore a reconstruction scheme in the background of the $f(T,\mathcal{T})$ gravity theory for different cosmological scenarios, where $T$ is the scalar torsion and $\mathcal{T}$ is the trace of the energy-momentum tensor. Using the reconstruction technique $f(T, \mathcal{T})$ Lagrangian is constructed for different cosmological eras such as dust, $ΛCDM$, perfect fluid, etc. Both minimal and non-minimal matter-coupled models are considered for this purpose. Different cosmological scenarios such as power law expansion, de-Sitter expansion, etc. have been considered, and using them Lagrangian functionals are constructed. Mathematical viabilities of all the constructed functionals have been investigated. The physical implications of the obtained solutions are discussed in detail. To check the cosmological compatibility of the constructed $f(T,\mathcal{T})$ functionals we have generated plots of important parameters like the equation of state parameter and deceleration parameter. It is seen that the reconstructed models are perfectly compatible with the late-time accelerated expansion of the universe.

gr-qc↗