arXiv subjects

Vinod Chandra

Publications and source records attributed to Vinod Chandra.

At least 55 records · Page 3Linked to original sources

arXiv2017

Collective excitations of a hot anisotropic QCD medium with Bhatnagar-Gross-Krook collisional kernel within an effective description

Collective modes of an anisotropic hot QCD medium have been studied within the semi-classical transport theory employing Bhatnagar-Gross-Krook (BGK) collisional kernel. The modeling of the isotropic medium is primarily based on a recent quasi-particle description of hot QCD equation of state where the medium effects have been encoded in effective gluon and quark/anti-quark momentum distributions that posses non-trivial energy dispersions. The anisotropic distribution functions are obtained in a straightforward the way by stretching or squeezing the isotropic ones along one of the directions. The gluon self-energy is computed using these distribution functions in a linearized transport equation with Bhatnagar-Gross-Krook (BGK) collisional kernel. Further, the tensor decomposition of gluon self-energy leads to the structure functions which eventually controls the dispersion relations and the collective mode structure of the medium. It has been seen that both the medium effects and collisions induce appreciable modifications to the collective modes and plasma excitations in the hot QCD medium.

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arXiv2017

Impact of momentum anisotropy and turbulent chromo-fields on thermal particle production in quark-gluon plasma medium

Momentum anisotropy present during the hydrodynamic evolution of Quark-Gluon Plasma (QGP) in RHIC may lead to chromo-Weibel instability and turbulent chromo-fields.The dynamics of the quark and gluon momentum distributions in this case is governed by an effective diffusive Vlasov equation (linearized). The solution of this linearized transport equation for the modified momentum distribution functions lead to the mathematical form of non-equilibrium momentum distribution functions of quarks/antiquarks and gluons. The modification to these distributions encode the physics of turbulent color fields and momentum anisotropy. In the present manuscript, we employ these distribution functions to to estimate thermal dilepton production rate in the QGP medium. The production rate is seen to have appreciable sensitivity to the strength of the anisotropy.

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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

Dissociation of heavy quarkonium in hot QCD medium in a quasi-particle model

Following a recent work on the effective description of the equations of state for hot QCD obtained from a Hard thermal loop expression for the gluon self-energy, in terms of the quasi-gluons and quasi- quark/anti-quarks with respective effective fugacities, the dissociation process of heavy quarkonium in hot QCD medium has been investigated. This has been done by investigating the medium modification to a heavy quark potential. The medium modified potential has a quite different form (a long range Coulomb tail in addition to the usual Yukawa term) in contrast to the usual picture of Debye screening. The flavor dependence of the binding energies of the heavy quarkonia states and the dissociation temperature have been obtained by employing the debye mass for pure gluonic and full QCD case computed employing the quasi-particle picture. Thus estimated dissociation patterns of the charmonium and bottomonium states, considering Debye mass from different approaches in pure gluonic case and full QCD, have shown good agreement with the other potential model studies.

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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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arXiv2015

Quark and gluon distribution functions in a viscous quark-gluon plasma medium and dilepton production via $q\bar{q}$-- annihilation

Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasi-particle description of the quark-gluon-plasma medium created in relativistic heavy-ion collision experiments. The model is described in terms of quasi-partons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis and the modifications to thermal distributions have been obtained by modifying the the energy momentum tensor in view of the non-trivial dispersion relations for the gluons and quarks. The interactions encoded in the equation of state induce significant modifications to the thermal distributions. As an implication, dilepton production rate in the $q\bar{q}$ annihilation process has been investigated. The equation of state is found to have significant impact on the dilepton production rate along with the viscosities.

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arXiv2015

Viscous modifications to quark and gluon distribution functions in quark-gluon plasma medium

Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasi-particle description of the quark-gluon-plasma medium created in relativistic heavy ion collision experiments. The model is described in terms of quasi-partons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis and the modifications to thermal distributions have been obtained by modifying the the energy momentum tensor in view of the non-trivial dispersion relations for the gluons and quarks. As an implication, dilepton production rate in the $q \bar{q}$ annihilation process has been investigated. Significant modifications have been observed in the dilepton production rate in the presence of interactions encoded in the QCD equation of state.

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arXiv2015

Impact of momentum-space anisotropy on heavy quark dynamics in a QGP medium

Momentum space anisotropy present in the quark and gluon distribution functions in relativistic heavy ion collisions induces Chromo-Weibel instability in the hot QCD medium created therein. The impact of the Chromo-Weibel instability on the dynamics of a heavy-quark (HQ) traversing in the QGP medium is investigated within the framework of kinetic theory by studying the momentum and temperature behavior of HQ drag and diffusion coefficients. The physics of anisotropy is captured in an effective Vlasov term in the transport equation. The effects of the instability are handled by making a relation with the phenomenologically known jet quenching parameter in RHIC and LHC. Interestingly, the presence of instability significantly affect the temperature and momentum dependences of the HQ drag and diffusion coefficients. These results may have appreciable impact on the experimental observables such as, the nuclear suppression factor, $R_{AA}(p_T)$, and the elliptic flow, $v_2(p_T)$, of heavy mesons in heavy ion collisions at RHIC and LHC energies which is a matter of future investigation.

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arXiv2014

Heavy Ion Collision evolution modeling with ECHO-QGP

We present a numerical code modeling the evolution of the medium formed in relativistic heavy ion collisions, ECHO-QGP. The code solves relativistic hydrodynamics in $(3+1)-$D, with dissipative terms included within the framework of Israel-Stewart theory; it can work both in Minkowskian and in Bjorken coordinates. Initial conditions are provided through an implementation of the Glauber model (both Optical and Monte Carlo), while freezeout and particle generation are based on the Cooper-Frye prescription. The code is validated against several test problems and shows remarkable stability and accuracy with the combination of a conservative (shock-capturing) approach and the high-order methods employed. In particular it beautifully agrees with the semi-analytic solution known as Gubser flow, both in the ideal and in the viscous Israel-Stewart case, up to very large times and without any ad hoc tuning of the algorithm.

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arXiv2013

Heavy-quark transport coefficients in a hot viscous quark-gluon plasma medium

The heavy-quark (HQ) transport coefficients have been estimated for a viscous quark-gluon plasma medium, utilizing a recently proposed quasi-particle description based on realistic QGP equation of state (EoS). Interactions entering through the equation of state significantly suppress the temperature dependence of the drag coefficient of QGP as compared to that of an ideal system of quarks and gluons. Inclusion of shear and bulk viscosities through the corrections to the thermal phase space factors of the bath particles alters the magnitude of the drag coefficient and the enhancement is significant at lower temperatures. The competition between the effects of realistic EoS and dissipative corrections through phase space factor the former eventually dictate how the drag coefficient would behave as a function of temperature, and how much quantitatively digress from the ideal case. The observations suggest significant impact of both the realistic equation of state, and the viscosities, on the HQs transport at RHIC and the LHC collision energies.

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arXiv2012

Transport properties of anisotropically expanding quark-gluon plasma within a quasi-particle model

The bulk and shear viscosities ($η$ and $ζ$) have been studied for quark-gluon-plasma produced in relativistic heavy ion collisions within semi-classical transport theory, in a recently proposed quasi-particle model of (2+1)-flavor lattice QCD equation of state. These transport parameters have been found to be highly sensitive to the interactions present in hot QCD. Contributions to the transport coefficients from both the gluonic sector and the matter sector have been investigated. The matter sector is found to be significantly dominating over the gluonic sector, in both the cases of $η$ and $ζ$. The temperature dependences of the quantities, $ζ/{\mathcal S}$, and $ζ/η$ indicate a sharply rising trend for the $ζ$, closer to the QCD transition temperature. Both $η$, and $ζ$ are shown to be equally significant for the temperatures that are accessible in the relativistic heavy ion collision experiments, and hence play crucial role while investigating the properties of the quark-gluon plasma.

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arXiv2011

On the bulk viscosity of anisotropically expanding hot QCD plasma

The bulk viscosity, $ζ$ and its ratio with the shear viscosity, $ζ/η$ have been studied in an anisotropically expanding pure glue plasma in the presence of turbulent color fields. It has been shown that the anisotropy in the momentum distribution function of gluons, which has been determined from a linearized transport equation eventually leads to the bulk viscosity. For the isotropic (equilibrium) state, a recently proposed quasi-particle model of pure SU(3) lattice QCD equation of state has been employed where the interactions are encoded in the effective fugacity. It has been argued that the interactions present in the equation of state, significantly contribute to the bulk viscosity. Its ratio with the shear viscosity is significant even at $1.5 T_c$. Thus, one needs to take in account the effects of the bulk viscosity while studying the hydrodynamic expansion of QGP in RHIC and LHC.

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arXiv2011

A quasi-particle description of $(2+1)$- flavor lattice QCD equation of state

A quasi-particle model has been employed to describe the $(2+1)$-flavor lattice QCD equation of state with physical quark masses. The interaction part of the equation of state has been mapped to the effective fugacities of otherwise non-interacting quasi-gluons and quasi-quarks. The mapping is found to be exact for the equation of state. The model leads to non-trivial dispersion relations for quasi-partons. The dispersion relations, effective quasi-particle number densities, and trace anomaly have been investigated employing the model.A Virial expansion for the EOS has further been obtained to investigate the role of interactions in quark-gluon plasma (QGP). Finally, Debye screening in QGP has been studied employing the model.

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arXiv2011

Strong Interactions, (De)coherence and Quarkonia

Quarkonia are the central objects to explore the non-perturbative nature of non-abelian gauge theories. We describe the confinement-deconfinement phases for heavy quarkonia in a hot QCD medium and thereby the statistical nature of the inter-quark forces. In the sense of one-loop quantum effects, we propose that the "quantum" nature of quark matters follows directly from the thermodynamic consideration of Richardson potential. Thereby we gain an understanding of the formation of hot and dense states of quark gluon plasma matter in heavy ion collisions and the early universe. In the case of the non-abelian theory, the consideration of the Sudhakov form factor turns out to be an efficient tool for soft gluons. In the limit of the Block-Nordsieck resummation, the strong coupling obtained from the Sudhakov form factor yields the statistical nature of hadronic bound states, e.g. kaons and Ds particles.

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arXiv2010

A geometric approach to correlations and quark number susceptibilities

We study the thermodynamic geometry arising from the free energy for the 2- and 3-flavor finite temperature hot QCD near the critical temperature. We develop a geometric notion for QCD thermodynamics, relating it with the existing microscopic quantities, e.g. quark-number susceptibility, which appears naturally within an approximately self-consistent resummation of perturbative QCD. We further incorporate thermal fluctuations in the free energy, thus yielding the geometric properties of local and global chemical correlations. These investigations are perturbative in nature. Nevertheless, one could apply the same line of thought for the geometric realization of underlying quark susceptibilities, either in the fabric of lattice QCD or in that of non-perturbative QCD.

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arXiv2010

Thermodynamic Geometric Stability of Quarkonia states

We compute exact thermodynamic geometric properties of the non-abelian quarkonium bound states from the consideration of one-loop strong coupling. From the general statistical principle, the intrinsic geometric nature of strongly coupled QCD is analyzed for the Columbic, rising and Regge rotating regimes. Without any approximation, we have obtained the non-linear mass effect for the Bloch-Nordsieck rotating strongly coupled quarkonia. For a range of physical parameters, we show in each cases that there exists a well-defined, non-degenerate, curved, intrinsic Riemannian manifold. As the gluons become softer and softer, we find in the limit of the Bloch-Nordsieck resummation that the strong coupling obtained from the Sudhakov form factor possesses exact local and global thermodynamic properties of the underlying mesons, kaons and $D_s$ particles.

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arXiv2010

On the Thermodynamic Geometry of Hot QCD

We study the nature of the covariant thermodynamic geometry arising from the free energy of hot QCD. We systematically analyze the underlying equilibrium thermodynamic configurations of the free energy of 2- and 3-flavor hot QCD with or without including thermal fluctuations in the neighborhood of the QCD transition temperature. We show that there exists a well-defined thermodynamic geometric notion for QCD thermodynamics. The geometry thus obtained has no singularity as an intrinsic Riemannian manifold. We further show that there is a close connection of this geometric approach with the existing studies of correlations and quark number susceptibilities in hot QCD.

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