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Vinod Chandra

Publications and source records attributed to Vinod Chandra.

68 records · Page 4Linked to original sources
arXiv2010

Quarkonia in anisotropic hot QCD medium in a quasi-particle model

The fate of heavy quarkonia states has been investigated in QCD at high temperature when the plasma has a small momentum space anisotropy within a quasi-particle model. A real time static potential has been obtained from a Hard thermal loop expression for the gluon self-energy, by employing the quasi-parton equilibrium distribution functions extracted from hot QCD equations of state of $O(g^5)$ and $O(g^6\ln(1/g))$. Employing the potential, quarkonia melting has been studied. It is found that the equations of state and the momentum anisotropy cause significant modifications in the screening properties of the plasma.

nucl-th↗
arXiv2010

A thermodynamic geometric study of Rényi and Tsallis entropies

A general investigation is made into the intrinsic Riemannian geometry for complex systems, from the perspective of statistical mechanics. The entropic formulation of statistical mechanics is the ingredient which enables a connection between statistical mechanics and the corresponding Riemannian geometry. The form of the entropy used commonly is the Shannon entropy. However, for modelling complex systems, it is often useful to make use of entropies such as the Rényi and Tsallis entropies. We consider, here, Shannon, Rényi, Tsallis, Abe and structural entropies, for our analysis. We focus on one, two and three particle thermally excited configurations. We find that statistical pair correlation functions, determined by the components of the covariant metric tensor of the underlying thermodynamic geometry, associated with the various entropies have well defined, definite expressions, which may be extended for arbitrary finite particle systems. In all cases, we find a non-degenerate intrinsic Riemannian manifold. In particular, any finite particle system described in terms of Rényi, Tsallis, Abe and structural entropies, always corresponds to an interacting statistical system, thereby highlighting their importance in the study of complex systems. On the other hand, a statistical description by the Gibbs-Shannon entropy corresponds to a non-interacting system.

cond-mat.stat-mech↗
arXiv2009

Charmonium suppression in the presence of dissipative forces in a strongly coupled quark-gluon plasma

We study the survival of charmonium states in a strongly-coupled quark-gluon plasma in the presence of dissipative forces. We consider first-order dissipative corrections to the plasma equation of motion in the Bjorken boost-invariant expansion with a strongly-coupled equation of state for QGP and study the survival of these states with the dissociation temperatures obtained by correcting the full Cornell potential not its Coulomb part alone with a dielectric function encoding the effects of deconfined medium. We further explore the sensitivity of prompt and sequential suppression of these states to the shear viscosity-to-entropy density ratio, $η/s$ from perturbative QCD and AdS/CFT predictions. Our results show excellent agreement with the recent experimental results at RHIC.

hep-ph↗
arXiv2009

Dissociation of 1 p quarkonium states in a hot QCD medium

We extend the analysis of a very recent work (Phys. Rev. {\bf C 80}, 025210 (2009)) to study the dissociation phenomenon of 1p states of the charmonium and bottomonium spectra ($χ_c$ and $χ_b$) in a hot QCD medium. This study employed a medium modified heavy quark potential which is obtained by incorporating both perturbative and non-perturbative medium effects encoded in the dielectric function to the full Cornell potential. The medium modified potential has a quite different form (a long range Coulomb tail in addition to the usual Yukawa term) compared to the usual picture of Debye screening. We further study the flavor dependence of their binding energies and dissociation temperatures by employing the perturbative, non-perturbative, and the lattice parametrized form of the Debye masses. These results are consistent with the predictions of the current theoretical works.

nucl-th↗
arXiv2009

Dissociation of quarkonium in hot QCD medium: Modification of the inter-quark potential

We have studied the dissociation of heavy quarkonium states in a hot QCD medium by investigating the medium modifications to a heavy quark potential. Our model shows that in-medium modification causes the screening of the charge in contrast to the screening of the range of the potential. We have then employed the medium-modified potential to estimate the dissociation pattern of the charmonium and bottomonium states and also explore how the pattern changes as we go from the perturbative to nonperturbative domain in the Debye mass. The results are in good agreement with the other current theoretical works both from the spectral function analysis and the potential model study.

hep-ph↗
arXiv2009

Quasi-particle model for lattice QCD: quark-gluon plasma in heavy ion collisions

We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for $T \ge 1.5T_c$. The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, {\it viz}, the shear viscosity, $η$ and the shear viscosity to entropy density ratio, $η/{\mathcal S}$. We find that both $η$ and $η/{\mathcal S}$ are sensitive to the interactions, and that the interactions significantly lower both $η$ and $η/\mathcal S$.

nucl-th↗
arXiv2009

On the chromoelectric permittivity and Debye screening in hot QCD

We study the response functions (chromo-electric susceptibilities) for an interacting quark-gluon plasma. The interaction effects have been encoded in the effective fugacities for quasi-partons which are extracted self-consistently from the two equations of state for hot QCD. The first one is the fully perturbative $O(g^5)$ EOS and, the second one which is $O(g^6\ln(1/g))$, incorporates some non-perturbative effects. We find that response function shows large deviations from the ideal behavior. We further determine the temperature dependence of the Debye mass by fixing the effective coupling constant $Q^2$ which appears in the transport equation. We show that our formalism naturally yields the leading order HTL expression for the Debye mass if we employ the ideal EOS. Employing the Debye mass, we estimate the dissociation temperatures for various charmonium and bottomonium bound states. These results are consistent with the current theoretical studies.

nucl-th↗
arXiv2009

$J/ψ$ suppression in nucleus-nucleus collisions

At high temperatures, strongly interacting matter becomes a plasma of deconfined quarks and gluons. In statistical QCD, deconfinement and the properties of the resulting quark-gluon plasma can be investigated by studying the in-medium behaviour of heavy quark bound states. In high energy nuclear interactions, quarkonia probe different aspects of the medium formed in the collision. So, we first reviewed the fate of quarkonia in the different stages of the (dynamical) system produced at the collision. We have then presented our present work on the dissociation of the heavy quarkonium states in a hot QCD medium by investigating the medium modifications to heavy quark potential. In contrast to the usual screening picture, interestingly our theory gives rise the screening of the charge, not the range of the potential.

nucl-th↗
arXiv2008

Viscosity and thermodynamic properties of QGP in relativistic heavy ion collisions

We study the viscosity and thermodynamic properties of QGP at RHIC by employing the recently extracted equilibrium distribution functions from two hot QCD equations of state of $O(g^5)$ and $O(g^6\ln(1/g))$ respectively. After obtaining the temperature dependence of energy density, and entropy density, we focus our attention on the determination of shear viscosity for a rapidly expanding interacting plasma, as a function of temperature. We find that interactions significantly decrease the shear viscosity. They decrease the viscosity to entropy density ratio, $η/{\mathcal S}$ as well.

nucl-th↗
arXiv2008

Hot QCD equations of state and response functions for quark-gluon plasma

We study the response functions (chromo-electric susceptibilities) of quark-gluon plasma as a function of temperature in the presence of interactions. We consider two equations of state for hot QCD. The first one is fully perturbative, of $O(g^5)$ EOS and, and the second one which is $O[g^6\ln(1/g)+δ]$, incorporates some non-perturbative effects. Following a recent work (Physical Review {\bf C 76}, 054909(2007)), the interaction effects contained in the EOS are encapsulated in terms of effective chemical potentials($\tildeμ$) in the equilibrium distribution functions for the partons.By using them in another recent formulation of the response functions({\tt arXiv:0707.3697}), we determine explicitly the chromo-electric susceptibilities for QCD plasma. We find that it shows large deviations from the ideal behavior. We further study the modification in the heavy quark potential due to the medium effects. In particular, we determine the temperature dependence of the screening lengths by fixing the effective coupling constant $Q$ which appears in the transport equation by comparing the screening in the present formalism with exact lattice QCD results. Finally, we study the dissociation phenomena of heavy quarkonium states such as $c\bar{c}$ and $b\bar{b}$, and determine the dissociation temperatures. Our results are in good agreement with recent lattice results.

hep-ph↗
arXiv2008

Hot QCD equations of state and RHIC

We show how hot QCD equations of states can be adapted to make definite predictions for quark-gluon plasma at RHIC. We consider equations of state up to $O(g^5)$ and $O[g^6(ln(1/g)+δ)]$. Our method involves the extraction of equilibrium distribution functions for gluons and quarks from these equations of state by capturing the the interaction effects entirely in the effective chemical potentials. We further utilize these distribution functions to study the screening length in hot QCD and dissociation phenomenon of heavy quarkonia states by combining this understanding with the semi-classical transport theory.

nucl-th↗
arXiv2007

Hot QCD equations of state and relativistic heavy ion collisions

We study two recently proposed equations of state (EOS) which are obtained from high temperature QCD, and show how they can be adapted to use them for making predictions for relativistic heavy ion collisions. The method involves extracting equilibrium distribution functions for quarks and gluons from the EOS, which in turn will allow a determination of the transport and other bulk properties of the quark gluon plasma. Simultaneously, the method also yields a quasi particle description of interacting quarks and gluons. The first EOS is perturbative in the QCD coupling constant and has contributions of $O(g^5)$. The second EOS is an improvement over the first, with contributions upto $ O(g^6 ln(\frac{1}{g}))$; it incorporates the nonperturbative hard thermal contributions. The interaction effects are shown to be captured entirely by the effective chemical potentials for the gluons and the quarks, in both the cases. The chemical potential is seen to be highly sensitive to the EOS. As an application, we determine the screening lengths which are, indeed the most important diagnostics for QGP. The screening lengths are seen to behave drastically differently depending on the EOS considered., and yield, therefore, a way to distinguish the two equations of state in heavy ion collisions.

nucl-th↗
arXiv2007

Chromo-electric Yang-Mills gauge fields

We obtain static gauge field configurations for SU(2) Yang-Mills gauge theory in the absence of chromo-magnetic field. We also present a systematic way to obtain such configurations for SU(3) and SU(4) YM gauge theories by realizing their Lie algebras in terms of SU(2). Generalization of our method to SU(N) gauge theory with N>2 is straight forward. The gauge fields thus obtained are complex. We investigated the issue of uniform as well as real chromo-electric field with these configurations. Furthermore, we investigated the possible class of vacuum solutions for the gauge fields and found that they are gauge inequivalent to the usual vacuum configuration $A^a_μ=0$.

hep-th↗