Faculty Bio

• Post-Doctoral Fellowship from Department of Atomic Energy (DAE) India, from January 2014 to September 2014.
• Post-Doctoral Fellowship from Spanish Ministry of Science and Innovation Spain, from May 2011 to October 2013.
• Post-Doctoral Fellowship from Department of Atomic Energy (DAE) India, from May 2008 to April 2011.
• JRF/SRF from Department of Atomic Energy (DAE) by India, from August           2001 to December 2007. (I got 95.6 percentile in the JEST entrance exam)

Thesis Supervised

• Ph.D: 1 (Ongoing)
• M.Sc:  9 (Completed) + 1 (Ongoing)
• B.Sc:  13(Completed) + 1 (Ongoing)

Research Summary
My research interests are focus on theoretical nuclear and astrophysics. A brief summary my doctoral and post doctoral research work is the following:

Doctoral Research
The Relativistic Mean Field (RMF) approach to quantum hadrodynamics has become a very popular tool to describe both finite nuclei and nuclear matter properties. But these models predict a stiff nuclear Equation of State (EoS) at higher densities which is not in good agreement with the experimental observations.

Furnstahl, Serot and Tang proposed an approach based on modern concepts of Effective Field Theory (EFT) and Density Functional Theory (DFT) for hadrons known as Effective field theory motivated Relativistic Mean Field (E-RMF) model. An E-RMF model contains all the non-renormalizable couplings consistent with the underlying symmetries of QCD. In this way, one recovers the standard non-linear σ−ω model (RMF) plus a few extra couplings. These extra couplings explains naturally the experimental observations of EoS without losing the advantages of the standard relativistic model for finite nuclei.

In my doctoral research work, Weanalyzed various properties of finite nuclei and nuclear matter in the framework of RMF and E-RMF models. A brief description of doctoral research work is the following:

• Super-Heavy Nuclei
  Traditionally a large gap in the single-particle spectrum has been interpreted as anindicator of a shell closure, at least of atomic number Z < 100. However, for a largenucleus such as a Super-Heavy Element (SHE), it may not be sufficient to simplydraw the single-particle level scheme and to look for the gaps, due to the complicated scheme and to look for the gaps, due to the complicated structure of thespectrum and the presence of levels with a high degree of degeneracy. Moreover, in a self-consistent calculation, a strong coupling between the neutron andproton shell structure takes place. Therefore, when dealing with SHE it is imperativeto look for other quantities to reliably identify the shell closures and magicnumbers, apart from the analysis of single-particle level structure. Sowe take into account several indicators to identify the occurrence of possible shellclosures, such as two-nucleon separation energies, two-nucleon shell gaps, average pairing gaps, and the shell correction energy. We predicts N=172 and Z=120 and N=258 and Z=120 as spherical doubly magic super-heavy nuclei, whereas N=184 and Z=114 show some magic character depending on the parameter set. The magicity of a particular neutron(proton) number in theanalyzed mass region is found to depend on the number of protons(neutrons) present in the nucleus.
• Clustering In Light and Super-Heavy Nuclei
  Clustering is a very general phenomenon, which appears in atomic, nuclear, subnuclear, and the cosmic worlds. We investigate the clustering phenomena in light, stable exotic and super-heavy nuclei within the framework of relativistic mean field approach by using the axially deformed harmonic oscillator basis. The standard BCS pairing scheme is adopted for taking the pairing into account. We use the calculated nucleon density distribution and deformationparametersto find the possible cluster configurations. In light nuclei, we are able to explain many of the well-established cluster structures in both ground and intrinsic excited states. This gives us enough confidence to apply this method in the super-heavy regions. In super-heavy we applied to Z=120, N=172-184 nuclei. A new ’bubble’-like structure for the Z=120, N=172, 292120 nucleus as signatures of doubly closed shells and two-cluster configuration for the Z=120,
  N=184, 304120 nucleus are some of the interesting results obtained.
• Equation of State and Neutron Star
  One of the most important problems in studies of dense objects like neutron stars is determining the Equation of State (EoS). Conventionally, neutron stars are one of the dense objects that represents the end point of the life cycle of stellar evolution.
  With a density span upto 10 times the saturation density (ρ0) and radius of ≈ 10 km, they evolve as a result of beautiful amalgamation of all the known forces in nature. Consequently, at such extreme condition several possibilities and forms of matter such as phase transition aspects, presence of exotic species or mixed phases (Quarkhyperon) could not be ruled out. Thus their study can review the implications from heavy-ion collision data or hyper-nuclei experiments. Further, we can relate such studies to many open astrophysical problems such as the supernovae collapse dynamics, the evolution of stellar structure and many such applications.

  We have shown that the E-RMF parameter sets give a soft EoS both around saturation and at high densities which is consistent with the measurements of kaon production and the flow of matter in energetic heavy-ion collisions, and with the observed neutron star masses and radii. We also study the properties of neutron star with an EoS with and without hyperons respectively. We employ E-RMF model including hyperons to describe the hadron phase. For the quark phase we have chosen to use both Unpaired Quark Matter (UQM) described by the MIT bag model and paired quarks described by the color-flavor locked (CFL) phase. We also built an EoS for the mixed matter by applying the charge neutrality condition and Gibbs criteria on hadron and quark phases. Our results are found in good agreement with recently imposed constraints on neutron star properties in the mass-radius plane and with the redshift interpreted therein. We have also shown that the EoS with UQM and CFL quark phases satisfies the constraint imposed by the recently measured redshift of 0.35 from three different transitions of the spectra of the x-ray binary EXO0748-676

Postdoctoral Research
In my six years of post-doctoral research, We have study the effect of symmetry energy and its density dependence to various phenomena from finite nuclei and neutron stars using of relativistic and non-relativistic mean field models.

The nuclear contribution to the difference between the binding energy of a system of all neutrons and another with equal numbers of protons and neutrons is known as the symmetry energy. We extended the RMF models with additional non-linear isoscalar-isovector couplings Λv, to obtained the constraints on symmetry energy from finite nuclei and to see the effect of Λv upon equation of state (EoS) of neutron star. We included the Λv coupling in two calibrated RMF parameter sets, NL3 and FSUGold. We generated all the combinations of Λv and gρ coupling by fixing symmetry energy around 26.00 MeV at an average density ρavg which corresponds to kF = 1.15 fm−1. The binding energy per particle of 208Pb and the proton density distributions are practically unaltered for all such combinations. A brief summary of our results is the following:

• Neutron Skin Thickness and Neutron Star : In finite nuclei, we find that the neutron skin thickness with higher Λv (i.e., soft symmetry energy) value is in good agreement with present experimental neutron skins data of antiprotonic atoms. In neutron star, except direct URCA process, different values of Λv have almost no effect in prediction of maximum mass, radius and kaon condensation. Our results also suggests that quartic coupling of vector meson coupling ζ have more contribution compare to Λv in softening the EoS of neutron star. However, Λv coupling is important in prediction of neutron skin thickness in various nuclei at higher neutron proton asymmetry.
• Liquid-Gas Phase Transition : We find symmetry energy have a significant influence on several features of liquid-gas phase transition in hot asymmetric nuclear matter. The boundary and area of the liquid-gas coexistence region, the maximal isospin asymmetry, and the critical values of pressure and isospin asymmetry, all of which systematically increase with increasing softness in the density dependence of symmetry energy. The critical temperature below which the liquid-gas mixed phase exists is found higher for a softer symmetry energy.
• Protoneutron Star : For hot and lepton-rich protoneutron stars we examined the possible liquid-gas phase transition near the crust comprising free nucleons and light clusters. Compared to free nucleon abundances, light clusters are found to dominate the particle yield at moderate and high temperatures in a uniform supernova matter. At very low densities, symmetry energy has a modest impact on the coexistence coexistence phase boundaries and on the equations of state of matter compared to thermal effects and on the number of trapped neutrinos. We also investigate the effect of symmetry energy on hyperon production in the dense interior of cold neutron stars and hot lepton-rich protoneutron. Our results suggests that a softer symmetry energy, in general, results in smaller chemical potentials that delay further the onset of hyperons and thereby reduced the hyperonization of the star matter.
• Unified Equation of State for Neutron Stars : We derive a new equation of state (EoS) for neutron stars (NS) from the outer crust to the core based on modern microscopic calculations using the Argonne v18 potential plus three-body forces computed with the Urbana model. To deal with the inhomogeneous structures of matter in the NS crust, we use a recent nuclear energy density functional that is directly based on the same microscopic calculations, and which is able to reproduce the ground-state properties of nuclei along the periodic table. The EoS of the outer crust requires the masses of neutron rich nuclei, which are obtained through Hartree-Fock-Bogoliubov calculations with the new functional when they are unknown experimentally. To compute the inner crust, Thomas-Fermi calculations in Wigner-Seitz cells are performed with the same functional. Existence of nuclear pasta is predicted in a range of average baryon densities between 0.067 fm−3 and 0.0825 fm−3 , where the transition to the core takes place. The NS core is computed from the new nuclear EoS assuming non-exotic constituents (core of npeμ matter). In each region of the star, we discuss the comparison of the new EoS with previous EoSs for the complete NS structure, widely used in astrophysical calculations. The new microscopically derived EoSfulfills at the same time a NS maximum mass of 2 MSun with a radius of 10 km, and 1.5 MNS with a radius of 11.6 km.
• Symmetry Energy and Inner Crust of Neutron Star : The inner crust of cold neutron star consist of electrons and a Coulomb lattice of neutron rich nuclei which is permeated by a gas of free neutrons. In this work, our main objective is to provide a relationship between symmetry energy and the crustal and global properties of neutron star in a consistent way. This aspect of neutron stars is not fully explored in previous studies. We define inner crust by Compressible Liquid Drop Model (CLDM). The CLDM provides a good description of the average microscopic properties of inner crust like mass, size, Wigner-Seitz cell size and density of dripped neutrons. We also include the pasta phases in our calculations to see the effects of these unusal shapes on neutron star properties and observational data

Future Research Plan
In continuation of my earlier work on neutron stars, I would like to extend, the analysis of cold dense matter and compact stars with an eye on the experimental and observational scenario. A brief summary of my future research plans is the following:

• Bulk Viscosity and r-Mode Instability in Compact Stars: One of the important factors in regulating the spins of compact stars is the r-mode oscillations. Various studies show that this instability is related to the bulk-viscosity of the star, which is as a result of the presence of exotic matter in neutron star interiors. Particularly, the presence of hyperons in the dense core of neutron stars can affect the bulk-viscosity and the r-mode instability would be completely suppressed. It will be interesting to study the r-mode instability taking hyperons into consideration for our further analysis. Further we can extend our work to look into other aspects, such as the possibility of gravitational waves from pulsars and can put theoretical limits on their detection.
• Rotating Neutron Stars : Neutron star are the densest form of cold matter in observable universe. Theoretically, the properties of neutron stars such as its mass, radius and related properties are the imprints of a particular equation of state (EoS). Rotating neutron stars, can potentially not only constrain the EoS of dense matter, but also interesting because they could be the source of gravitational wave radiation, the mechanism which is believed to take away the star angular momentum thereby resulting in the slow down of the stars. Also recent results obtained from different sources has raised crucial implications on the nature of EoS. It is important to probe the various aspects of an EoS in detail and emphasize the need of constraints.
• Existence of Dark Matter in Neutron Stars: Observations of the kinematics of self-gravitating objects such as galaxies and clusters of galaxies give strong hint of the existence of dark matter (DM).
  Cosmological observations tell us that this invisible matter cannot consist of baryons, it must be a new kind of matter which interacts with the rest of the standard model particles very weakly. The exact nature of the dark matter, its coupling between standard model particles and the mass is still not known. In this work, we are planning to study an impact of asymmetric dark matter on properties of the neutron stars and their ability to reach the two solar masses limit, which allows us to present a new range of masses of dark matter particles and their fractions inside the star. Our analysis is based on the observational fact of the existence of two pulsars reaching this limit and on the theoretically predicted reduction of the neutron star maximal mass caused by the accumulation of dark matter in its interior.

I am teaching B.Tech and Int. M.Sc. (Physics/Chemistry) since 2014. A list of theory and lab courses is the following:
Theory

• Modern Physics
• Physics of Semiconductor Devices
• Astronomy
• Computational Physics
• Advanced Quantum Mechanics
• Nuclear and Particle Physics
• Astrophysics and Cosmology

Experiment

• Basic Physics
• Optics, Heat and Electricity
• Mechanics and Properties of Matter
• Electricity and Magnetism
• Simulation Lab

Course Design
I design the syllabus of the following courses:

• Introduction to Solar Physics
• Astrophysics and Cosmology
• Relativistic Quantum Mechanics
• Nuclear and Particle Physics
• Computational Physics
• Advanced Particle Physics
• Theory of Nanostructure
• Physics of Compact Stars

Other Professional Assignments

• Co-Director of SERC school “Nuclear Physics from New Perspectives” held at the Department of Physics, Bharathiar University from 07-27 February 2017.
• Staff in charge of astronomy club “ASTHA”, Amrita Vishwa Vidyapeetham Coimbatore, India, since 2014.
• Assistant Secretary of “Alumni association”, Institute of Physics, Bhubaneswar, India, from 2002 to 2003.