Currently, I (Dr. Bharat Kumar) am a postdoc in Center for Computer Sciences at University of Tsukuba, Japan. I am working in the field of nuclear theory and astrophysics focusing mainly on developing nuclear energy density functionals of the relativistic mean-field model and have recently generated and tested two newly parameter sets (IOPB-I and G3) in different regimes such as finite nuclei, infinite nuclear matter, and neutron star. Also, I use the equation of state of neutron-star matter to calculate stellar properties of the neutron star such as composition, mass, radii, moments of inertia, tidal deformability, and gravitational wave emissions. My research publications can be found on my Google Scholar page or in my ORCID account. I have created a forum to bring together nuclear scientists from all over the world for presenting and discussing their research findings and experiences.

Highlights of my important papers

In collaboration led by Dr. Philippe Landry, we have used equation-of-state (EoS) insensitive relations between neutron star (NS) observables to translate the GW170817 canonical tidal deformability measurement into bounds on the properties of all neutron stars. In particular, if we assume a common neutron star EoS, then GW170817 constrains radii, moment-of-inertia and tidal deformability for other binary NS and pulsar systems. These quasi-universal relations can further be used to combine separate X-ray and GW observations independently of the EoS, leading to joint constraints on tidal deformability.

In collaboration with Dr. Philippe Landry, we present a means of inferring the moment of inertia of any NS of known mass from a separate tidal deformability measurement. The inference deploys the well-established I-Love and binary Love relations in a novel way: these universal relations have never been combined to translate observations of a neutron star from one system to constraints on the properties of a neutron star from another. The measurement is highly anticipated by astronomers, neutron-star astrophysicists, gravitational physicists and nuclear theorists because of its ability to probe the unknown equation of state of ultra-dense matter---the object of what is undoubtedly a major unsolved problem in physics. Ours is moreover the first study of GW170817's implications for the neutron-star moment of inertia, as well as the first attempt to constrain PSR J0737-3039A's moment of inertia based on astrophysical observations, rather than nuclear theory.

My Colleagues and I found that the tidal deformability is very strongly correlated with the linear combinations of the slopes of nuclear isoscalar incompressibility and symmetry energy coefficients, all fall-outs of the nuclear equation of state. For the first time, we also found that the tidal deformability is approximately proportional to the sixth power of the radius of neutron star for a wide range of neutron star masses. This relation together with the bounds on the tidal deformability obtained from the GW170817 and its UV/optical/infrared electromagnetic counterparts constrain the radius of the neutron star with canonical mass in the range 11.82 - 13.72 km.

I and my colleagues have developed two new parameter sets for the energy density functional such as G3 and IOPB-I for finite nuclei, and infinite nuclear matter system within the effective field theory motivated relativistic mean field (ERMF) formalism. The isovector part of the ERMF model employed in the present study includes the coupling of nucleons to the δ and ρ mesons and the cross-coupling of ρ mesons to the σ and ω mesons. The results for the finite and infinite nuclear systems obtained using our parameter sets are in harmony with those data extracted from various experiments. In particular, the neutron-skin thickness of Pb-208 nucleus and canonical radius of the neutron star are compatible with the GW170817. The low-density behavior of the equation of state for pure neutron matter is in good agreement with other microscopic models. Also, we calculate the maximum mass, and tidal deformability which are in quite well with the GW170817 as well as with the pulsar data.