Research Highlights
Neutron star cooling
References: Physical Review C, 108, 035801 (2023)
The nuclear symmetry energy and its density-dependent characteristics have been recently assessed with heightened precision through the PREX-2 experiment. This refined set of values facilitates the examination of the viability of the direct Urca neutrino emission process within the highly dense interiors of neutron stars. Leveraging this novel perspective, we undertake an investigation into the cooling rates of neutron stars possessing canonical masses, and subsequently, we compare these findings with available observational data pertaining to neutron star cooling. Our analysis indicates that a substantial portion of the thermal profiles exhibited by isolated neutron stars align with the cooling behavior expected of canonical mass stars, even accounting for the effects of superfluidity suppression.
Neutron star asteroseismology
References: Physical Review D, 107, 103054 (2023)
A comprehensive assemblage of equations of state (EOSs), formulated within the framework of the covariant density functional theory, is utilized to investigate the polar f- and p-oscillations occurring in both cold and hot compact stars. These EOSs incorporate density dependent couplings, allowing for a thorough examination of the oscillations. Our findings reveal that the oscillation frequencies of nucleonic stars are diminished by finite temperature effects, while the opposite outcome is observed for stars featuring exotic particle degrees of freedom. Notably, when employing the Γ-law to construct EOSs at finite temperature, the estimation errors in oscillation mode frequencies range from approximately 10% to 30%, contingent upon the mass of the stars.
Quark matter studies
References: Monthly Notices of the Royal Astronomical Society, 513, 3788 (2022); Physical Review D, 107, 063024 (2023)
The nuclear symmetry energy and its density-dependent characteristics have been recently assessed with heightened precision through the PREX-2 experiment. This refined set of values facilitates the examination of the viability of the direct Urca neutrino emission process within the highly dense interiors of neutron stars. Leveraging this novel perspective, we undertake an investigation into the cooling rates of neutron stars possessing canonical masses, and subsequently, we compare these findings with available observational data pertaining to neutron star cooling. Our analysis indicates that a substantial portion of the thermal profiles exhibited by isolated neutron stars align with the cooling behavior expected of canonical mass stars, even accounting for the effects of superfluidity suppression.
(Anti)kaon condensation in neutron star matter
References: Physical Review D,102, 123007 (2020); 103, 063004 (2021); Physical Review C,107, 035807 (2023)
Recent measurements of neutron star mass from several candidates set the lower bound on the maximum possible mass for this class of compact objects ∼2 M⊙. Existence of stars with high mass brings the possibility of existence of exotic matter (hyperons, meson condensates) at the core region of the objects. We investigate the (anti)kaon condensation in β-equilibrated nuclear matter within the framework of covariant density functional theory. The functionals in the kaonic sector are constrained by the experimental studies on (anti)kaons atomic, kaon-nucleon scattering data fits.
Δ-resonances admixed hypernuclear dense matter
References: Physical Review D, 103, 063004 (2021); Physical Review C, 105, 015802 (2022)
We study the effect of (anti)kaon condensation on the properties of compact stars that develop hypernuclear cores with and without an admixture of Δ-resonances. The density-dependent parameters in the hyperonic sector are adjusted to the data on Λ and Ξ− hypernuclei data. The Δ-resonance couplings are tuned to the data obtained from their scattering off nuclei and heavy-ion collision experiments. We find that (anti)kaon condensate leads to a softening of the equation of state and lower maximum masses of compact stars than in the absence of the condensate. The (anti)kaons condensations occur through a second-order phase transition, which implies no mixed-phase formation. For large values of (anti)kaon and Δ-resonance potentials in symmetric nuclear matter, we observe that condensation leads to an extinction of cascade hyperons.
Constraining dense matter in light of gravitational-wave observations
References: Monthly Notices of the Royal Astronomical Society, 507, 2991 (2021); 513, 3788 (2022)
The detection of gravitational waves (GWs) from the merger of binary neutron star (NS) events (GW170817 and GW190425) and subsequent estimations of tidal deformability play a key role in constraining the behaviour of dense matter. Strict bounds from GWs and massive NS observations constrain the theoretical models of nuclear matter comportment at large density regimes. On the other hand, model parameters providing the highly dense matter response are bounded by nuclear saturation properties. Considering these constraints together, we study possible models and parametrization schemes with the feasibility of exotic degrees of freedom in dense matter which go well with the astrophysical observations as well as the terrestrial laboratory experiments. Astrophysical observations are well explained if the inclusion of heavier non-strange baryons is considered as one fraction of the dense matter particle spectrum.
Ascendancy of nuclear symmetry energy on compact star observables
References: Physical Review C, 105, 015802 (2022); Thapa & Sinha, arXiv: 2203.02272 (2022); EPJ Web of Conferences (Vol. 279, p. 10003) (2023)
We study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). The slope of symmetry energy parameter is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of symmetry energy slope at saturation favour early appearance of non-strange baryons in comparison to hyperons leading to latter's threshold at higher matter densities. We also investigate the dependence of symmetry energy slope on tidal deformability and compactness parameter of a 1.4 M⊙ neutron star for different equation of states and observe similar converging behaviour for larger symmetry energy slope values. Based on recent updated value of neutron-skin thickness from PREX-2 data, further information regarding dense matter behavior can be extracted.
Dense matter behavior in presence of strong magnetic fields
References: Particles,3, 660 (2020); Springer Proceedings in Physics(Vol. 277), p. 755–759 (2022); Physical Review C,107, 035807 (2023)
A particular class of neutron stars, namely magnetars are reported to possess huge magnetic fields trillions of times that of the Earth's magnetic field. We construct a new equation of state for the baryonic matter under an intense magnetic field within the framework of covariant density functional theory. The extension of the nucleonic functional to the hypernuclear sector is constrained by the experimental data on Λ and Ξ- hypernuclei. We find that the equation of state stiffens with the inclusion of the magnetic field, which increases the maximum mass of neutron star compared to the non-magnetic case. In addition, the strangeness fraction in the matter is enhanced. Several observables, like the Dirac effective mass, particle abundances, etc. show typical oscillatory behavior as a function of the magnetic field and/or density which is traced back to the occupation pattern of Landau levels.
To have a glimpse of where I exhibited my research work till date as talks/ presentations, please visit the Talks page.
Future projects
• Thermal properties of dense matter
• Di-baryonic condensation in dense matter
• Dark matter in neutron stars
For more details of my research work, please visit the Publications page.
Journal peer-reviewer
• Monthly Notices of the Royal Astronomical Society
• Physical Review & Physical Review Letters (American Physical Society)
Collaborators
• Dr. Monika Sinha, Indian Institute of Technology Jodhpur, Rajasthan-342037, India
• Prof. Armen Sedrakian, Frankfurt Institute for Advanced Studies, Ruth-Moufang-Straße, 60438 Frankfurt am Main, Germany
• Prof. Debades Bandopadhyay (retd.), Saha Institute of Nuclear Physics, Kolkata, West Bengal-700064, India
• Prof. Adriana R. Raduta, National Institute of Physics and Nuclear Engineering (IFIN-HH), Bucharest, Romănia
• Prof. Gargi Chaudhuri, Variable Energy Cyclotron Centre, Kolkata, West Bengal-700064, India
• Dr. Jia Jie Li, School of Physical Science and Technology, Southwest University, Chongqing 400700, China
• Dr. Mikhail V. Beznogov, National Institute of Physics and Nuclear Engineering (IFIN-HH), Bucharest, Romănia
• Dr. Rana Nandi, Department of Physics, Polba Mahavidyalaya, Hooghly, West Bengal-712148, India
• Dr. Trisha Sarkar, Indian Institute of Technology Jodhpur, Rajasthan-342037, India
• Mr. Anil Kumar, Indian Institute of Technology Jodhpur, Rajasthan-342037, India
• Dr. Vishal Parmar, Indian Institute of Technology Jodhpur, Rajasthan-342037, India
• Dr. Jaikhomba Singha, University of Cape Town, South Africa
• Mr. Suman Pal, Variable Energy Cyclotron Centre, Kolkata, West Bengal-700064, India
• Mr. Soumen Podder, Variable Energy Cyclotron Centre, Kolkata, West Bengal-700064, India
