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Theoretical Physics

We focus on developing fundamental models to explore structures in nuclear matter phase diagram

  • Multifragmentation and asymmetric nuclear matter equation of state (EOS) in intermediate energy nucleus-nucleus collisions
  • Quark-Gluon-Plasma formed at ultra-relativistic energy heavy ion collisions.

Multifragmentation and nuclear asymmetry energy

𝜂/𝑠 in Multifragmentation

Statistical nuclear multifragmentation (SMM) model was developed to investigate the nuclear breakup mechanism. The model exhibits thermodynamic of liquid-gas-phase transition comprising of a nucleus at low temperature (liquid phase) nucleons at high temperature (gas phase) and intermediate mass fragments (liquid-gas mixed phase). The transport properties namely the shear viscosity to entropy density ratio 𝜂/𝑠 in multifragmentation estimated in SMM shows a minimum near the critical temperature Tc = 5 MeV and sensitive the break-up volume

Asymmetric nuclear matter EOS

Relativistic mean field (RMF) model with isoscalar-isovector coupling Λν was formulated to constrain the density dependence of nuclear symmetry energy of 𝐸sym(ρ). The correlation between the neutron-skin thickness of various nuclei and 𝐸sym(ρ) obtained by tuning Λν coupling was studied. Agreement with measured skin dictates a softer 𝐸sym(ρ) at subsaturation densities that translates to stiff symmetry energy at supranormal densities.


Collective anisotropic flow

Anisotropic flow is a response to the anisotropies in the initial geometry of the system created in heavy-ion collisions. A hybrid model was constructing by coupling A MultiPhase Transport (AMPT) model (for initial fluctuating geometry and pre-equilibrium dynamics) to a relativistic (2+1)- dimensional viscous hydrodynamic model (for subsequent near-equilibrium evolution). For Pb-Pb collisions at LHC, the model described remarkably well the data for the anisotropic flow coefficients 𝑣𝑛 (𝑝 τ) = ⟨cos 𝑛(𝜑 − 𝜓𝑛 )⟩ for 𝑛 = 2 – 6 with a constant 𝜂/𝑠 = 0.12 at various collision centralities.

Principal component analysis (PCA) method

Principal component analysis (PCA) method was applied to study event-by-event flow fluctuations. This new method provides all informations in the two-particle correlations in a physically transparent way and enables to study the leading (α = 1) as well as subleading ( α = 2, 3, 4) modes of fluctuations of particle number 𝑣0, elliptic flow 𝑣2 and triangular flow 𝑣3 with pseudorapidity.

Formulation of relativistic dissipative hydrodynamics

Relativistic viscous hydrodynamic equations were derived invoking the second law of thermodynamics where all the second-order transport coefficients were uniquely determined within a single framework. The calculated bulk relaxation time τΠ = ζ/P removed the long-standing ambiguity for the unknown τΠ (generally taken to be the relaxation time of shear viscosity τπ) and prevents the occurrence of cavitation (negative longitudinal pressure PL = P + Π - π < 0).

Hydrodynamic (Thermal) fluctuations

Produced locally due to finite particle density and during the entire space-time evolution of the system. The hydrodynamic fluctuations propagate by diffusion over large space-times and can have measurable contribution on the two-particle correlations (though these vanish on ensemble averaging). The magnitude and shape of the two-particle rapidity correlations are sensitive to viscous evolution equations, viz. Navier-Stokes, Muller-Israel-Stewart, Chapman-Enskog as well as on the shear viscosty to entropy density ratio 𝜂/𝑠 .