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Bijay K. Agrawal

Publications and source records attributed to Bijay K. Agrawal.

3 recordsLinked to original sources

NucleiML: A machine learning framework of ground-state properties of finite nuclei for accelerated Bayesian exploration

The global behavior of the nuclear equation of state (EoS) is commonly studied using data from finite nuclei (FN), heavy-ion collisions, and astrophysical observations of neutron stars (NS). The constraints derived from FN such as binding energies and charge radii play the most crucial role in shaping the EoS up to saturation density. The computational cost associated with explicitly incorporating these constraints presents a significant challenge especially when the aim is to explore the model uncertainties rather than optimizing a single model. We address this by introducing NucleiML (NML), a machine learning framework trained on ground-state properties of a few finite nuclei generated by a relativistic mean-field model. NML allows us to integrate FN and NS properties within a Bayesian inference framework in an efficient manner. The results demonstrate reasonable accuracy and a speedup of $\sim 10^4$ times for calculation of FN properties for a single parameter set, yielding roughly $\sim 10^3 \times$ speed up in the Bayesian framework. The present study makes the case for extending the work to a larger set of nuclei, potentially enabling future studies of NS properties to incorporate the whole nuclear chart.

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Probing the impact of Delta-Baryons on Nuclear Matter and Non-Radial Oscillations in Neutron Stars

The presence of heavy baryons, such as $Δ$-baryons and hyperons can significantly impact various properties of Neutron Stars (NSs), like oscillation frequencies, dimensionless tidal deformability, mass, and radii. We explored these effects within the Density-Dependent Relativistic Mean Field formalism. Our analysis considered $Δ$-admixed NS matter in both hypernuclear and hyperon-free scenarios, providing insights into particle compositions and their effects on NS properties. Our study of non-radial $f$-mode oscillations revealed a distinct increase in frequency due to the additional baryons. The degree of increase was significantly influenced by the meson-baryon coupling strengths. Notably, the coupling between $Δ$-resonances and $σ$-mesons played a highly influential role. In some cases, it led to an approximately 20\% increase in the $f$-mode oscillation frequency of canonical NSs. These couplings also affect other bulk properties of NSs, including mass, radii, and dimensionless tidal deformability ($Λ$). Comparing our results with available observational data from pulsars (NICER) and gravitational waves (LIGO-VIRGO collaboration), we found strong agreement, particularly concerning $Λ$.

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Impact of the equation of state on $f$- and $p$- mode oscillations of neutron stars

We investigate the impact of the neutron-star matter equation of state on the $f$- and $p_1$-mode oscillations of neutron stars obtained within the Cowling approximation and linearized general relativity. The $f$- and $p_1$-mode oscillation frequencies, and their damping times are calculated using representative sets of Skyrme Hartree-Fock and relativistic mean-field models, all of which reproduce nuclear systematics and support $2M_\odot$ neutron stars. Our study shows strong correlations between the frequencies of $f$- and $p_1$-modes and their damping times with the pressure of $β$-equilibrated matter at densities equal to or slightly higher than the nuclear saturation density $ρ_0$. Such correlations are found to be almost independent of the composition of the stars. The frequency of the $p_1$-mode of $1.4M_\odot$ star is strongly correlated with the slope of the symmetry energy $L_0$ and $β$-equilibrated pressure at density $ρ_0$. Compared to GR calculations, the error in the Cowling approximation for the $f$-mode is about 30\% for neutron stars of low mass, whereas it decreases with increasing mass. The accuracy of the $p_1$-mode is better than 15\% for neutron stars of maximum mass, and improves for lower masses and higher number of radial nodes.

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