arXiv subjects

Sukanya Mitra

Publications and source records attributed to Sukanya Mitra.

At least 37 records · Page 2Linked to original sources

arXiv2021

Correspondence between momentum dependent relaxation time and field redefinition of relativistic hydrodynamic theory

In this article a correspondence has been established between the out of equilibrium system dissipation and the thermodynamic field redefinition of the macroscopic variables through the momentum dependent relaxation time approximation (MDRTA) solution of relativistic transport equation. Here, it has been shown that the out of equilibrium thermodynamic fields are not uniquely defined and are subjected to include dissipative effects from the medium. A second order relativistic hydrodynamic theory has been developed including such dissipative effects. The necessary conditions for developing a hydrodynamic theory has been fulfilled, (i) the thermodynamic identities incorporating such redefined fields have been shown to conserve the energy-momentum tensor perfectly under MDRTA, (ii) the non-negativity of entropy production remains unaffected by the inclusion of such dissipative contributions in hydro fields as long as the independent transport coefficients remain positive.

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arXiv2021

Relativistic hydrodynamics with momentum dependent relaxation time

A second order relativistic hydrodynamic theory has been derived using momentum dependent relaxation time in the relativistic transport equation. In order to do that, an iterative technique of gradient expansion approach, namely Chapman-Enskog (CE) expansion of the particle distribution function has been employed. The key findings of this work are, (i) momentum dependent relaxation time in collision term results in an extended Landau matching condition for the thermodynamic variables, (ii) the result from numerical solution of Boltzmann equation lies somewhere in between the two popular extreme limits : linear and quadratic ansatz, indicating a fractional power of momentum dependence in relaxation time to be appropriate, (ii) an equivalence has been established between the iterative gradient expansion method like CE and the well known moment approach like Grad's 14-moment method.

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arXiv2020

Thermal and viscous dissipation in relativistic heavy ion collisions

We investigate the effects of finite baryon density and temperature on the bulk properties of matter formed in relativistic heavy ion collisions within second-order dissipative hydrodynamics. The relativistic fluid evolution equations for heat flow and shear stress tensor are derived from kinetic theory by using Grad's 14-moment approximation for the single-particle phase-space distribution function. The new equations provide a number of additional terms associated with heat-shear couplings as compared to the existing derivations based on entropy principle. The dissipative equations are encoded in non-boost-invariant hydrodynamic model simulation and studied for the evolution of high baryon density matter encountered at the beam energy scan program at RHIC. We find that thermal dissipation dominates shear pressure in defining the bulk observables at the low energy but its effect diminishes at ultra-relativistic energies.

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arXiv2019

Optical properties of an anisotropic hot QCD medium

The present investigation involves explorations on the chromo-dielectric properties of the hot QCD medium produced in relativistic heavy-ion collisions in terms of refractive index. The isotropic/equilibrium modelling is done within an effective quasi-particle model of hot QCD medium. The possibilities of negative refraction in the medium are also explored in terms of the Depine-Lakhtakia index. The anisotropic aspects of the hot QCD medium are incorporated by introducing the anisotropy in a particular direction. That makes the medium quite similar to uniaxial crystals, and hence we observe phenomenon of birefringence ( two distinct refractive indices in the anisotropic case). Interestingly, both anisotropy and medium effects play significant roles in deciding the optical properties of the hot QCD/Quark-Gluon-Plasma (QGP) medium.

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arXiv2019

Relativistic second order dissipative hydrodynamics from effective fugacity quasi particle model

In this work a second order relativistic viscous hydrodynamic model has been presented based on the effective fugacity quasi-particle model (EQPM). The hydro model has been derived from the effective relativistic second-order transport equation under EQPM for a multi-particle (two component) system and solving it in Grad's 14 moment method. The EQPM model describes the strongly interacting thermal system of QCD interactions through its fugacity parameters extracted from an updated lattice equations of state. The proper time evolution of temperature and pressure anisotropy is observed to be affected significantly due to the inclusion of EQPM model compared to an ideal system.

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arXiv2018

Transport coefficients of hot magnetized QCD matter beyond the lowest Landau level approximation

In this article, shear viscosity, bulk viscosity, and thermal conductivity of a hot QCD medium have been studied in the presence of a strong magnetic field. To model the hot magnetized QCD matter, an extended quasi-particle description of the hot QCD equation of state in the presence of the magnetic field has been adopted. The effects of higher Landau levels on the temperature dependence of viscous coefficients (bulk and shear viscosities) and thermal conductivity have been obtained by considering the $1\rightarrow 2$ processes in the presence of the strong magnetic field. An effective covariant kinetic theory has been set up in (1+1)-dimensional that includes mean field contributions in terms of quasi-particle dispersions and magnetic field to describe the Landau level dynamics of quarks. The sensitivity of these parameters to the magnitude of the magnetic field has also been explored. Both the magnetic field and mean field contributions have seen to play a significant role in obtaining the temperature behaviour of the transport coefficients of hot QCD medium.

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arXiv2018

Relaxation of baryon diffusion flow in QGP medium and its impact on thermal photon spectra

In the current work the time evolution of baryon diffusion flow within the scope of second order relativistic hydrodynamic theory has been studied for a 2-component quark-gluon system. The relaxation time for diffusion flow is estimated using the Grad's moment method of many particle kinetic theory. The temperature dependence of relaxation time for diffusion flow has been obtained for different quark chemical potentials. Finally, the diffusion equation has been solved for a $1+1$ dimensional boost invariant system and the effect of diffusion flow has been studied on the thermal photon spectra in a baryon rich environment. The present analysis on the role of baryon number diffusion in influencing the properties of hot QCD medium could be relevant for the baryon rich matter explorations in upcoming experimental facilities.

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arXiv2018

Covariant kinetic theory for effective fugacity quasi particle model and first order transport coefficients for hot QCD matter

An effective relativistic kinetic theory has been constructed for an interacting system of quarks, anti-quarks and gluons within a quasi-particle description of hot QCD medium at finite temperature and baryon chemical potential, where the interactions are encoded in the gluon and quark effective fugacities with non-trivial energy dispersions. The local conservations of stress-energy tensor and number current require the introduction of a mean field term in the transport equation which produces non-vanishing contribution to the first order transport coefficients. Such contribution has been observed to be significant for the temperatures which are closer to the QCD transition tem- perature, however, induces negligible contributions beyond a few times the transition temperature. As an implication, impact of the mean field contribution on the the temperature dependence of the shear viscosity, bulk viscosity and thermal conductivity of a hot QCD medium in the presence of binary, elastic collisions among the constituents, has been investigated. Visible effects have been observed for the temperature regime closer to the QCD transition temperature.

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arXiv2017

Medium effects on the electrical conductivity of a hot pion gas

The electromagnetic response of an interacting system of pions has been studied at finite temperature. The corresponding transport parameter i.e. electrical conductivity has been estimated by solving the relativistic transport equation in presence of a finite electric field employing the Chapman-Enskog technique where the collision term has been treated in the relaxation time approximation. The scattering amplitudes of charged pions modeled by $ρ$ and $σ$ meson exchange using an effective Lagrangian have been obtained at finite temperature by introducing self-energy corrections in the thermal propagators in the real time formalism. The temperature behavior of electrical conductivity for a hot pion gas shows significant quantitative enhancement due to the inclusion of medium effects in scattering.

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arXiv2017

Thermodynamics and relativistic kinetic theory for q-generalized Bose-Einstein and Fermi-Dirac systems

The thermodynamics and covariant kinetic theory have been elaborately investigated in a non-extensive environment considering the non-extensive generalization of Bose-Einstein (BE) and Fermi-Dirac (FD) statistics. Starting with Tsallis' entropy formula, the fundamental principles of thermostatistics have been established for a grand canonical system having q-generalized BE/FD degrees of freedom. The many particle kinetic theory has been set up in terms of the relativistic transport equation with q-generalized Uehling-Uhlenbeck collision term. The conservation laws have been realized in terms of appropriate moments of the transport equation. The thermodynamic quantities have been obtained in weak non-extensive environment for a massive pion-nucleon and a massless quark-gluon system with non-zero baryon chemical potential. In order to get an estimate of the impact of non-extensivity on the system dynamics, the q-modified Debye mass and hence the q-modified effective coupling have been estimated for a quark-gluon system.

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arXiv2017

In-medium viscous coefficients of a hot hadronic gas mixture

We estimate the shear and the bulk viscous coefficients for a hot hadronic gas mixture constituting of pions and nucleons. The viscosities are evaluated in the relativistic kinetic theory approach by solving the transport equation in the relaxation time approximation for binary collisions ($ππ$,$πN$ and $NN$). Instead of vacuum cross-sections usually used in the literature we employ in-medium scattering amplitudes in the estimation of the relaxation times. The modified cross-sections for $ππ$ and $πN$ scattering are obtained using one-loop modified thermal propagators for $ρ$, $σ$ and $Δ$ in the scattering amplitudes which are calculated using effective interactions. The resulting suppression of the cross sections at finite temperature and baryon density is observed to significantly affect the $T$ and $μ_N$ dependence of the viscosities of the system.

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arXiv2017

$Δ$ self-energy at finite temperature and density and the $πN$ cross-section

The self energy of $Δ$-baryon is evaluated at finite temperature and density using the real time formalism of thermal field theory. The Dyson-Schwinger equation is used to get the exact thermal propagator followed by the spectral function of $Δ$. The $πN$ scattering cross section obtained using explicit $Δ$ exchange is normalized to the experimental data in vacuum and its medium modification is implemented by means of the exact thermal propagator. A significant suppression of the peak of the cross-section is observed at higher temperature and baryon density. Effects on the mean relaxation time of nucleons and the temperature dependence of the shear viscosity of a pion nucleon gas are demonstrated.

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arXiv2017

Transport coefficients of a hot QCD medium and their relative significance in heavy-ion collisions

The main focus of this article is to obtain various transport coefficients for a hot QCD medium that is produced while colliding two heavy nuclei ultra-relativistically. As the hot QCD medium follows dissipative hydrodynamics while undergoing space-time evolution, the knowledge of the transport coefficients such as thermal conductivity, electrical conductivity, shear and bulk viscosities are essential to understand the underlying physics there. The approach adopted here is semi-classical transport theory. The determination of all these transport coefficients requires knowledge of the medium away from equilibrium. In this context, we setup the linearized transport equation employing the Chapman-Enskog technique from kinetic theory of many particle system with a collision term that includes the binary collisions of quarks/antiquarks and gluons. In order to include the effects of a strongly interacting, thermal medium, a quasi-particle description of realistic hot QCD equation of state has been employed through the equilibrium modeling of the momentum distributions of gluons and quarks with non-trivial dispersion relations while extending the model for finite but small quark chemical potential. The effective coupling for strong interaction has been redefined following the charge renormalization under the scheme of the quasiparticle model. The consolidated effects on transport coefficients are seen to have significant impact on their temperature dependence. The relative significances of momentum and heat transfer as well as charge diffusion processes in hot QCD have been investigated by studying the ratios of the respective transport coefficients.

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arXiv2017

Collective excitations of hot QCD medium in a quasi-particle description

Collective excitations of a hot QCD medium are the main focus of the present article. The analysis is performed within semi-classical transport theory with isotropic and anisotropic momentum distribution functions for the gluonic and quark-antiquark degrees of freedom that constitutes the hot QCD plasma. The isotropic/equilibrium momentum distributions for gluons and quarks are based on a recent quasi-particle description of hot QCD equations of state. The anisotropic distributions are just the extensions of isotropic ones by stretching or squeezing them in one of the directions. The hot QCD medium effects in the model adopted here enter through the effective gluon and quark fugacities along with non-trivial dispersion relations leading to an effective QCD coupling constant. Interestingly, with these distribution functions the tensorial structure of the gluon polarization tensor in the medium turned out to be similar to the one for the non-interacting ultra-relativistic system of quarks/antiquarks and gluons . The interactions mainly modify the Debye mass parameter and , in turn, the effective coupling in the medium. These modifications have been seen to modify the collective modes of the hot QCD plasma in a significant way.

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arXiv2016

Thermal Relaxation, Electrical Conductivity and Charge Diffusion in a Hot QCD Medium

The response of electromagnetic (EM) fields that are produced in non-central heavy-ion collisions to electromagnetically charged quark gluon plasma can be understood in terms of charge transport and charge diffusion in the hot QCD medium. This article presents a perspective on these processes by investigating the temperature behavior of the related transport coefficients, {\it viz.} electrical conductivity and the charge diffusion coefficients along with charge susceptibility. In the process of estimating them, thermal relaxation times for quarks and gluons have been determined first. These transport coefficients have been studied by solving the relativistic transport equation in the Chapman-Enskog method. For the analysis, $2\rightarrow 2$, quark-quark, quark-gluon and gluon-gluon scattering processes are taken into account along with an effective description of hot QCD Equations of state (EOSs) in terms of temperature dependent effective fugacities of quasi-quarks (anti-quarks) and quasi-gluons. Both improved perturbative hot QCD EOSs at high temperature and a lattice QCD EOS are included for the analysis. The hot QCD medium effects entering through the quasi-particle momentum distributions along with an effective coupling, are seen to have significant impact on the temperature behavior of these transport parameters along with the thermal relaxation times for the quasi-gluons and quasi-quarks

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arXiv2016

Diffusion of hidden charm mesons in hadronic medium

The drag and diffusion coefficients of a hot hadronic medium have been evaluated by using hidden charm mesons as probes. The matrix elements for the evaluation of these coefficients are calculated using an effective theory as well as from scattering lengths. Although the transport coefficients show a significant rise with temperature its effects on the suppression of $J/ψ$ in hadronic matter is not significant.

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arXiv2015

Medium effects on the relaxation of dissipative flows in a hot pion gas

The relaxation times over which dissipative fluxes restore their steady state values have been evaluated for a pion gas using the 14-moment method. The effect of the medium has been implemented through a temperature dependent pi-pi cross-section in the collision integral which is obtained by including one-loop self-energies in the propagators of the exchanged rho and sigma mesons. To account for chemical freeze out in heavy ion collisions, a temperature dependent pion chemical potential has been introduced in the distribution function. The temperature dependence of the relaxation times for shear and bulk viscous flows as well as the heat flow is significantly affected.

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arXiv2014

Medium effects on the thermal conductivity of a hot pion gas

We investigate the effect of the medium on the thermal conductivity of a pion gas out of chemical equilibrium by solving the relativistic transport equation in the Chapman-Enskog and relaxation time approximations. Using an effective model for the pi-pi cross-section involving rho and sigma meson exchange, medium effects are incorporated through thermal one-loop self-energies. The temperature dependence of the thermal conductivity is observed to be significantly affected.

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