arXiv subjects

Debanjan Guha Roy

Publications and source records attributed to Debanjan Guha Roy.

4 recordsLinked to original sources

arXiv2026

$K^-$-Driven Direct Urca Cooling in Rotating Neutron Stars: A Bayesian Study

We investigate the onset of antikaon ($K^-$) condensation and its implications for the equation of state (EoS) and cooling of neutron stars (NSs) within density-dependent relativistic mean-field parametrisations DD2 and MPE. Treating the antikaon - nucleon optical potential ($U_K$) as a free parameter in the range $[-180,-60]$ MeV, we constrain it using Bayesian inference with NICER mass-radius observations of PSR J0030+0451 and PSR J0740+6620. The inferred posterior distributions favour strongly attractive in-medium $K^-$ interactions, while their broad widths indicate only weak constraints on $U_K$ by astrophysical observations. More attractive values of $U_K$ lead to an earlier onset of $K^-$ condensation, enhanced softening of the EoS, and lower Direct Urca (DU) threshold densities. The condensation threshold is systematically lower in DD2 than in MPE, while finite entropy further promotes the onset of rapid cooling. The $K^-$-induced enhancement of the proton fraction ($y_p$) substantially affects a larger volume of the stellar core, i.e. capable of sustaining rapid DU cooling. We further show that rapid rotation suppresses DU cooling by reducing the central density and $y_p$, thereby shrinking the DU-active core. This suppression is more pronounced for MPE than for DD2. Our results demonstrate that $K^-$ condensation, finite entropy, and rotation jointly exert a strong influence on the conditions for rapid neutrino cooling in NSs.

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arXiv2025

Signatures of $K^-$ condensation on neutron star structure and $f-$mode frequencies

Antikaon ($K^-$) condensation within neutron star matter (NS) depends on the antikaon-nucleon interaction potential ($U_K$). Appearance of $K^-$ generally softens the equation of state (EOS). The impact of this softening on the structure of the NS can be leveraged to find a telltale sign of the phase transition from nucleonic matter to $K^-$ condensation. To investigate the impact of $K^-$ condensation on NS properties using a Bayesian inference framework, we choose two sets of RMF model parameters to obtain a stiff (DD2) and relatively soft (FSU) nucleonic EOS, and explore a wide range of optical potential depths. Multimessenger observations from NICER and LIGO/Virgo constrain the optical potential values to $U_K = -104.72^{+13.82}_{-12.48}$ MeV and $U_K = -66.46^{+2.47}_{-3.42}$ MeV for the stiff and soft cases, respectively. Deeper $K^-$ potentials trigger condensation at a lower density, softening the EOS and lowering the corresponding maximum masses. While slopes of mass-radius and tidal deformability curves overlap between nucleonic and exotic EOSs, their curvature and $f-$mode oscillation properties (frequency and damping time) reveal features attributable to EOS softening. However, distinguishing the specific exotic degrees of freedom responsible for the softening remains an open challenge.

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arXiv2024

Bayesian evaluation of hadron-quark phase transition models through neutron star observables in light of nuclear and astrophysics data

We investigate the role of hybrid and nucleonic equations of state (EOSs) within neutron star (NS) interiors using Bayesian inference to evaluate their alignment with recent observational data from NICER and LIGO-Virgo (LV) collaborations. We find that smooth hybrid EOSs are slightly favoured in explaining NS mass-radius relations, particularly for pulsars such as PSR J0030+0451 and PSR J0740+6620. However, this preference is not definitive, as gravitational wave (GW) data does not significantly differentiate between our hybrid and nucleonic models. Our analysis also reveals tensions between older NICER data and recent measurements for PSR J0437-4715, highlighting the need for more flexible EOS models. Through two sampling approaches - one fixing the hadronic EOS set and the other without fixing the same, we demonstrate that the hybrid EOS model can incorporate stiffer EOSs, resulting in a better agreement with NICER data but leading to higher tidal deformability, which is less consistent with GW observations. In some recent publications a parameter $d_c$, related to the trace anomaly and its derivative, is used to indicate the presence of deconfined quark matter. We find that our hadronic model, which does not include phase transition to deconfined matter, under the influence of imposed constraints, is able to predict values below 0.2 for $d_c$ at around five times saturation density. The hybrid model goes below this threshold at lower densities under the same conditions.

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arXiv2024

Analysis of Neutron Star $f-$mode Oscillations in General Relativity with Spectral Representation of Nuclear Equations of State

We study quasinormal $f-$mode oscillations in neutron star(NS) interiors within the linearized General Relativistic formalism. We utilize approximately 9000 nuclear Equations of State (EOS) using spectral representation techniques, incorporating constraints on nuclear saturation properties, chiral Effective Field Theory ($χ$EFT) for pure neutron matter, and perturbative Quantum Chromodynamics (pQCD) for densities pertinent to NS cores. The median values of f-mode frequency, $ν_f$ (damping time, $τ_f$) for NS with masses ranging from 1.4 - 2.0 $M_\odot$ lie between 1.80 - 2.20 kHz (0.13 - 0.22 s) for our entire EOS set. Our study reveals a weak correlation between $f-$mode frequencies and individual nuclear saturation properties, prompting the necessity for more intricate methodologies to unveil multi-parameter relationships. We observe a robust linear relationship between the radii and $f-$mode frequencies for different NS masses. Leveraging this correlation alongside NICER observations of PSR J0740+6620 and PSR J0030+0451, we establish constraints that exhibit partial and minimal overlap for observational data from Riley et al. and Miller et al. respectively with our nucleonic EOS dataset. Moreover, NICER data aligns closely with radius and frequency values for a few hadron-quark hybrid EOS models. This indicates the need to consider additional exotic particles such as deconfined quarks at suprasaturation densities. We conclude that future observations of the radius or $f-$mode frequency for more than one NS mass, particularly at the extremes of viable NS mass scale, would either rule out nucleon-only EOS or provide definitive evidence in its favour.

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