arXiv subjects

Prasanta Kumar Das

Publications and source records attributed to Prasanta Kumar Das.

At least 19 recordsLinked to original sources

arXiv2026

Bayesian Constraints on Inverse-Tangent Inflation with Constant-EOS Reheating and a Dynamical Reheating Analysis

We perform a Bayesian inference analysis of an inflationary model based on an inverse-tangent potential, incorporating reheating dynamics in both constant and dynamical equation-of-state (DEOS) frameworks. Using Planck and ACT constraints on the scalar spectral index, we find preferred values $\kappa\simeq0.5-0.6$ and $N_k\simeq40-60$, leading to reheating temperatures $T_{RH}\sim10^{10}-10^{14}$ GeV and reheating durations $N_{RH}\sim3-36$ e-folds. Reheating weighted $H_0$ posteriors shift the Planck inference towards the ACT preferred region through the intrinsic $n_s-H_0$ degeneracy of the CMB likelihood. In the DEOS framework, reheating with a constant decay rate yields $N_{RH}\simeq4-8$ e-folds and $T_{RH}\simeq10^{13}$ GeV, while a dynamical decay rate produces a strong dependence on the Yukawa coupling $y$, with $N_{RH}$ varying from $\mathcal{O}(30)$ to $\mathcal{O}(1)$ e-folds and the reheating temperature spanning $\sim10^{-2}-10^{14}$ GeV. Imposing inflation-reheating consistency significantly restricts the viable parameter space to a narrow region around $n_s\simeq0.9720-0.9725$ and $r\simeq0.026-0.060$, demonstrating that reheating dynamics provide a nontrivial bridge between early-universe inflation and late-time cosmological parameter inference.

astro-ph.CO↗

arXiv2026

First Constraints on the Ellipticities of Self-Interacting Fermionic Dark Matter Admixed Neutron Stars from Continuous Gravitational-Wave Searches

We investigate continuous gravitational-wave (CW) emission from rapidly rotating, non-axisymmetric, isolated neutron stars admixed with self-interacting fermionic dark matter (DM) and hosting DM-induced equatorial deformations (``dark mountains''). In particular, we develop a formalism that describes how DM accumulation inside the star changes its structure, how dark mountains arise from an anisotropic distribution of DM inside it, and how the star's moment of inertia and thus the amplitude of its GW emission is increased compared to that of an ordinary neutron star. Moreover, using results from all-sky searches for CWs from non-axisymmetric neutron stars performed with LIGO O3 data, we place the first constraints on the DM-induced ellipticities $\varepsilon$ of DM-admixed neutron stars across the full GW frequency range analyzed by LIGO and for a range of self-interaction strengths. With the same data, we also exclude portions of the DM-mass/self-interaction coupling strength parameter space that would have produced detectable GW signals in LIGO O3 data. We rule out at best (at worst) couplings $g\gtrsim10^{-5.5}$ ($g\gtrsim 10^{-4}$) for DM-admixed neutron stars with ellipticities $\varepsilon=10^{-7}$ ($\varepsilon=10^{-9}$) at distances $d=1$ ($d=10$) kpc away for DM masses of $m_\chi\in[0.1,10]$ GeV. Furthermore, we show that even larger regions of this parameter space will become accessible to next-generation detectors, such as Einstein Telescope and Cosmic Explorer, with exclusions as strong as $g\gtrsim10^{-6}$ for neutron stars located $d=10$ kpc away for $\varepsilon=10^{-7}$. Our results demonstrate that searches for CWs naturally provide a direct probe of dark mountains sustained by DM-admixed neutron stars.

astro-ph.CO↗

arXiv2026

Impacts of {$f(R, T)$} gravity on neutron stars study within the relativistic mean-field model framework in light of GW170817, Pulsars and NICER data

In this work, we investigate the neutron star structure in conservative $f(R, T)$ gravity with $f(R, T)=R+λT$, where $λ$ denotes the matter--geometry coupling. The modified stellar structure equations are solved using realistic relativistic mean-field (RMF) equations of state (EOSs), including density-dependent linear models and nonlinear interacting models with meson self-couplings. Theoretical predictions are confronted with multimessenger constraints from heavy pulsars, NICER radius measurements, and GW170817 tidal deformability, imposing $M_{\max}\simeq 2.07\, M_{\odot}$ and $10.62~\mathrm{km}<R_{1.4}<12.83~\mathrm{km}$ to constrain both the EOS parameter space and $λ$. We find that density-dependent EOSs such as DDH$_δ$ and TW satisfy all observational constraints for specific $λ$ ranges, while nonlinear EOSs (NL3, GM1, TM1), despite large maximum masses, fail to simultaneously satisfy radius and tidal bounds even in modified gravity. The maximum neutron star mass is highly sensitive to the matter--geometry coupling and exhibits a strong degeneracy with the EOS, consistent with previous studies. The additional term in the modified Tolman--Oppenheimer--Volkoff equations alters the pressure gradient, affecting EOS stiffness and the speed of sound squared $c_s^2$, while preserving causality ($c_s^2/c^2<1$). Pearson and Kendall analyses reveal a strong negative correlation between mass, radius, and $λ$ ($-0.18$ and $-0.23$, respectively). Our results show that modified gravity alone cannot compensate for unrealistic dense-matter physics, highlighting the necessity of realistic EOSs and joint multimessenger constraints, and establish conservative $f(R,T)$ gravity as a viable strong-field extension of General Relativity.

astro-ph.CO↗

arXiv2025

Thermal Evolution of Magnetars under f(R, T) Gravity

The present study explores the thermal evolution and emission properties of neutron stars within the framework of modified $f(R, T)$ gravity by solving the coupled energy-balance and heat-transport equations. We compute stellar mass and pressure profiles by solving the Tolman-Oppenheimer-Volkoff equations in both Einstein gravity and modified gravity, employing the APR, FPS, and SLy equations of state, with and without the strong magnetic field. Using these profiles, we assess the red-shifted surface temperature, $T_s^{\infty}$, as well as the photon and neutrino luminosities for each equation of state. We further examine the effects of the magnetic field, the choice of equation of state, and the underlying gravity theory framework on the cooling of neutron stars, particularly those of magnetized neutron stars or magnetars. Our results indicate that $f(R, T)$ gravity, particularly for the APR and SLy equations of state, exhibits improved agreement with the observed $T_s^{\infty}$ and photon luminosities than standard general relativity, regardless of magnetic-field strength. Moreover, it predicts the neutrino luminosities under both gravity models, all the chosen equations of state, and magnetic field configurations.

gr-qc↗

arXiv2025

Reheating and Inflationary dynamics driven by an inverse tangent potential

In this work, we study the early universe inflation and the post-inflation reheating era employing an inverse tangent potential of the form $V=V_0 \cdot[tan^{-1}(\frac{κϕ}{m_p})]^2$, where $κ$ is a free parameter of the potential and $m_p$ is the reduced Planck mass. We derive the slow roll parameters, the number of e-folds(N), the scalar spectral index $n_s$, the tensor-to-scalar ratio $r$, and the tensor spectral index $n_T$ for the inverse tangent potential. We examine the inflationary observables using the data of the Planck-2018 and recent ACT collaboration and obtain constraints on the potential parameter $κ$. We also employ a reheating analysis by invoking the conservation of entropy between today and the time when reheating starts. We obtain bounds on the reheating temperature $T_{re}$ and the number of e-folds of the reheating $N_{re}$ using the spectral-index $n_s$ constraints from Planck 2018 and the ACT results. We show that this inverse-tangent potential can act as an alternative to the standard inflationary potentials like Starobinsky which are excluded at $2σ$ level by the recent sixth data release (DR6) of the Atacama Cosmology Telescope (ACT) collaboration.

astro-ph.CO↗

arXiv2025

Structural Properties of Magnetized Neutron Stars under f (R, T ) Gravity Framework

The current work investigates the structural properties of neutron stars in the presence of a strong magnetic field within the framework of f(R,T) modified gravity, where the matter-geometry coupling leads to deviations from general relativity at high matter densities. We present here the mass-radius sequences, as well as the mass and pressure distributions for various values of the modified gravity parameter and the central magnetic field. The modified Tolman-Oppenheimer- Volkoff equations are numerically solved using isotropic equations of state, specifically the APR, FPS, and SLy models. Comparing the corresponding results in the context of general relativity suggests that more negative values of the modified gravity parameter result in higher maximum gravitational masses. In contrast, strong central magnetic fields of up to 1018 Gauss cause only a slight decrease in maximum mass without disrupting spherical symmetry. Our findings are in agreement with the observed data from GW170817, PSR and NICER.

gr-qc↗

arXiv2025

Revealing Dark Matter's Role in Neutron Stars Anisotropy: A Bayesian Approach Using Multi-messenger Observations

Dark matter (DM) continues to evade direct detection, but neutron stars (NSs) serve as natural laboratories where even a modest DM component can alter their structure. While many studies have examined DM effects on NSs, they often rely on specific choices of equations of state (EOS) models, assume isotropy, and lack a Bayesian statistical framework, limiting their predictive power. In this work, we present a Bayesian framework that couples pressure-anisotropic nuclear EOS to a self-interacting fermionic DM component, constrained by NICER and GW170817 data. Our results show that DM mass fractions up to $\sim10\%$ remain consistent with current data, which softens the high-density EOS, leading to reduced stellar radii and tidal deformabilities while requiring negligible pressure anisotropy. Bayesian model comparison reveals no statistically significant preference between pure baryonic and DM-admixed NSs, indicating that DM inclusion enhances physical realism without complexity penalties. However, existing data cannot tightly constrain the DM parameters, and our empirical radius definition introduces a systematic bias toward the DM core configurations. To address this, we therefore introduce the DM radius span $ΔR_χ\equiv R_{χ,\mathrm{max}} - R_{χ,\mathrm{min}}$ as a unified diagnostic for DM distributions. This parameter simultaneously characterizes core-halo transition features while exhibiting strong linear correlations ($ΔR_χ< 4\,\mathrm{km}$) with both DM and BM parameters, providing a clear avenue for future constraints. Our approach bridges current limitations and future potential in probing DM through compact star observations.

astro-ph.HE↗

arXiv2025

Revisiting the Inert Scalar Dark Matter with Vector-like Quarks

The inert doublet model (IDM), a minimal extension of the Standard Model (SM), provides a scalar dark matter (DM) candidate that belongs to the additional Higgs doublet. The model faces challenges in achieving the correct relic abundance for compressed spectra and DM masses in the high-mass range. In this work we introduce a $Z_2$-odd singlet vector-like quark (VLQ) into the IDM framework that helps us alleviate these issues and provide new channels of contributions to the relic abundance. The VLQ not only enhances the DM relic abundance for masses above $~550$ GeV but also eases constraints from direct detection experiments by enabling smaller couplings between the inert scalars and the SM Higgs. We analyze the impact of the VLQ on DM phenomenology, including relic density, direct and indirect detection constraints. The results demonstrate that the extended IDM framework not only resolves existing limitations in the compressed spectrum but also offers exciting prospects for detection in current and future collider experiments.

hep-ph↗

arXiv2024

Constructing Viable Interacting Dark Matter and Dark Energy Models: A Dynamical Systems Approach

We study the evolution of $k=-1$ FLRW cosmological models for two interacting Dark Matter-Dark Energy Models using dynamical system analysis. Since we are interested in late time evolution, the sign of the interaction term is chosen such that it facilitates the transfer of energy from dark matter to dark energy. We also explore the $k=0$ invariant subspace of these models. We find that both these models have sectors which have a stable fixed point where we can recover an accelerating universe with a negative equation of state. This indicates these can be viable models for our universe. We also rule out certain sectors of these models because they do not give the correct late time observational features. We observe that although we start with a dust-like Dark Matter, its effective equation of state evolves due to its interaction with Dark Energy. As a result, the Dark Matter can display features of stiff matter and exotic matter in the course of evolution.

gr-qc↗

arXiv2024

Implications of Fermionic Dark Matter Interactions on Anisotropic Neutron Stars

The presence of Dark matter (DM) within a neutron star (NS) can substantially influence the macroscopic properties. It is commonly assumed that the pressure inside an NS is isotropic, but in reality, pressure is locally anisotropic. This study explores the properties of anisotropic NS with a subfraction of DM (isotropic) trapped inside. Implementing a two-fluid formalism with three Equations of State (EOS): AP3 (a realistic nucleon-nucleon interaction model), BSk22 (modeling atomic nuclei and neutron-matter), and MPA1 (considering relativistic effects in nuclear interactions). The properties of NS, such as mass ($M$), radius ($R$), and dimensionless tidal deformability ($Λ$), for various DM-anisotropic configurations, have been rigorously tested against observational constraints. These constraints include data from the binary NS merger GW170817, NICER x-ray measurements, and pulsar mass-radius observations. We observe that with increasing DM subfraction, higher anisotropies could also satisfy the observational constraints. Furthermore, increasing the coupling ($g$) between DM and its mediator leads to the formation of a core-halo structure, with a DM halo surrounding the baryonic matter (BM). Specifically, for coupling values of $g = 10^{-4}$, $10^{-3.7}$, and $10^{-3.5}$, we observe that the maximum radius ($R_{max}$) decreases with increasing anisotropy, which contrasts with the behavior at $g = 10^{-5}$ and in scenarios with no DM. Our analysis indicates that binary pulsar systems could potentially constrain the extent of admixed anisotropic NS or, more optimistically, provide evidence for the existence of DM-admixed anisotropic NS.

astro-ph.CO↗

arXiv2023

Exploring the Electromagnetically Interacting Dark Matter at the International Linear Collider

Dark Matter being electrically neutral does not participate in electromagnetic interactions at leading order. However, we discuss here fermionic dark matter (DM) with permanent magnetic and electric dipole moment that interacts electromagnetically with photon at loop-level through a dimension-5 operator. We discuss the search prospect of the dark matter at the proposed International Linear Collider (ILC) and constrain the parameter space in the plane of the DM mass and the cutoff scale $Λ$. At the 500 GeV ILC with $4$ ab$^{-1}$ of integrated luminosity we probed the mono-photon channel and utilizing the advantages of beam polarization we obtained an upper bound on the cutoff scale that reaches up to $Λ= 3.72$ TeV.

hep-ph↗

arXiv2023

Jet substructure probe to unfold singlet-doublet dark matter in the presence of non-standard cosmology

We examine the singlet-doublet fermionic dark matter model, where the non-thermal production of the dark matter in light of a non-standard cosmology demands a significantly large interaction rate than the typical radiation-dominated Universe. Despite being a model of freeze-in light dark matter and heavy mediator, the characteristic long-lived particle searches at the collider experiment and the displaced vertex signature do not help in probing such a dark sector since this non-standard interaction mandates nearly prompt decay. We make a counterproposal to probe such signal with di-fat-jets generated from the boosted decays of massive vector bosons and Standard Model Higgs, along with the substantial missing transverse momentum to probe the dark matter at LHC. Interestingly, substructure variables associated with these fat jets have an additional handle to tackle the extensive QCD background as it encodes implicit footmarks of their origin. We adopt the multivariate analysis with the booted decision tree to constrain the measured relic density allowed parameter space of dark matter in the presence of the modified cosmological scenario. Our study shows how the non-trivial expansion affects dark matter production in the early Universe and alters the required search strategies at colliders. This probe provides the best discovery prospect at the HL-LHC for extended parameter space now opened up in the dark sector.

hep-ph↗

arXiv2023

SN1987A cooling due to Plasmon-Plasmon scattering in the Randall-Sundrum Model

The light braneworld radion, stabilized via the Goldberger-Wise mechanism in the Randall-Sundrum model, can be produced copiously inside the supernova core due to plasmon-plasmon annihilations. The radion, thus produced, subsequently decays to a neutrino-antineutrino pair and takes away the energy released in the SN1987A explosion. Assuming that the supernovae cooling rate for any new physics channel(Raffelt's criterion) $\dot{\varepsilon}(γ_Pγ_P \stackrelϕ{\longrightarrow} ν_τ \overlineν_τ) \leq 7.288\times 10^{-27} \rm{GeV}$, we find the lower bound on the radion vacuum expectation value $\langleϕ\rangle \sim 3$~TeV for $m_ϕ= 30$ MeV corresponding to the deformation parameter $q=1.17$ in the Tsallis statistics formalism. In the scenario with $q=1$, we find $\langleϕ\rangle = 178$ GeV for $m_ϕ= 30$ MeV.

hep-ph↗

arXiv2023

Non-Minimal Inflation with a scalar-curvature mixing term $\frac{1}{2} ξR ϕ^2$

We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $ϕ$ in the presence of the non-minimal scalar-curvature mixing term $\frac{1}{2}ξR ϕ^2$. We consider four distinct scalar field potentials $ϕ^p e^{-λϕ},~(1 - ϕ^{p})e^{-λϕ},~(1-λϕ)^p$ and $\frac{αϕ^2}{1+αϕ^2}$ to study inflation in the non-minimal gravity theory. We calculate the potential slow-roll parameters and predict the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$, in the parameters ($λ, p, α$) space of the potentials. We have compared our results with the ones existing in the literature, and this indicates the present status of non-minimal inflation after the release of the PLANCK 2018 data.

astro-ph.CO↗

arXiv2022

EFT analysis of leptophilic dark matter at future electron-positron colliders in the mono-photon and mono-$Z$ channels

We consider the possibility that dark matter (DM) only interacts with the Standard Model leptons, but not quarks at tree level, and analyze the future lepton collider prospects of such leptophilic DM in the monophoton and mono-$Z$ (both leptonic and hadronic) channels. Adopting a model-independent effective field theory framework, we consider all possible dimension-six operators of scalar-pseudoscalar (SP), vector-axial vector (VA), and tensor-axial tensor (TAT) types for a fermionic DM and derive the collider sensitivities on the effective cutoff scale $Λ$ as a function of the DM mass. As a concrete example, we take the beam configurations of the International Linear Collider with $\sqrt s=1$ TeV and $8$ ab$^{-1}$ integrated luminosity, including the effect of beam polarization, and show that it can probe leptophilic DM at $3σ$ level up to $Λ$ values of $6.6$, $8.8$, and $7.1$ TeV for the SP-, VA- and TAT-type operators, respectively. This is largely complementary to the direct and indirect searches for leptophilic DM and can potentially provide the best-ever sensitivity in the low-mass DM regime.

hep-ph↗

arXiv2022

Inflationary Cosmology in a non-minimal $f(R,T)$ gravity theory using a $RT$ mixing term

We investigate a class of inflationary models in modified gravity theories which contain a non-minimal coupling between gravity and a scalar field $ϕ$ (inflaton) as $f(R,T)=R \bigl(1+α+ κ^4 βT \bigr)+κ^2γT $ where $κ^2=8πG$ where $G$ is the Newton's constant. We consider two inflaton potentials of the form (i) $V = V_0 \bigl(1 +\lnϕ \bigr)$ and (ii) $V_0\frac{λϕ^p}{1+λϕ^p}$. For a range of potential parameters, we explored the constraints on modified gravity parameters i.e. ($α$, $β$ and $γ$) in three categories -- (i) $β\neq0$, $α=γ=0$ (considering $R$ and $RT$ mixing terms), (ii) $α=0$, $γ\neq0$, $β\neq 0$ ($RT$ mixing term along with $T$ and $R$ terms) and (iii) $γ=0$, $α\neq0$, $β\neq0$ ($RT$ mixing term along with $R$ term) for the above two potentials. The inclusion of $RT$ mixing term provides the scalar spectral index $n_s$ up to $3σ$ limit of PLANCK data, which is $n_s=0.9649\pm0.0042$ as well as the tensor-to-scalar ratio $r<0.106$ and the e-fold parameter $40<N<70$ for both the potentials.

gr-qc↗

arXiv2022

Observational Constraints on the $f(ϕ,T)$ gravity theory

We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $ϕ$ and the trace of the energy momentum tensor $T$ as $f(ϕ,T) = 2 ϕ( κ^{1/2} αT + κ^{5/2} βT^2) $ to the Einstein-Hilbert action. We consider a class of inflaton potentials (i) $V_0 ϕ^p e^{-λϕ}$, (ii) $V_0\frac{ λϕ^p}{1+λϕ^p}$ and investigate the sensitivity of the modified gravity parameters $α$ and $β$ on the inflaton dynamics. We derive the potential slow-roll parameters, scalar spectral index $n_s$, and tensor-to-scalar ratio $r$ in the above $f(ϕ,T)$ gravity theory and analyze the following three choices of modified gravity parameters~(i) Case I:~ $α\neq 0, ~β=0$ i.e. neglecting higher order terms, (ii) Case II:~ $α=0$, $β\neq 0$~ and do the analysis for $T^2$ term, (iii) Case III:~ $α\neq 0$ and $β\neq 0$ i.e. keeping all terms. For a range of potential parameters, we obtain constraints on $α$ and $β$ in each of the above three cases using the WMAP and the PLANCK data.

gr-qc↗

arXiv2022

Inflationary Cosmology in the Modified $f(R, T)$ Gravity

In this work, we study the inflationary cosmology in modified gravity theory $f(R, T) = R + 2 λT$ ($λ$ is the modified gravity parameter) with three distinct class of inflation potentials (i) $ϕ^p e^{-αϕ}$, (ii) $(1-ϕ^p)e^{-αϕ}$ and (iii) $\frac{αϕ^2}{1+αϕ^2}$ where $α$, $p$ are the potential parameters. We have derived the Einstein equation, potential slow-roll parameters, the scalar spectral index $n_s$, tensor to scalar ratio $r$, and tensor spectral index $n_T$ in modified gravity theory. We obtain the range of $λ$ using the spectral index constraints in the parameter space of the potentials. Comparing our results with PLANCK 2018 data and WMAP data, we found out the modified gravity parameter $λ$ lies between $-0.37<λ<1.483$.

gr-qc↗