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R. S. Bhalerao

Publications and source records attributed to R. S. Bhalerao.

At least 19 recordsLinked to original sources
arXiv2007

Aspects of causal viscous hydrodynamics

We investigate the phenomenology of freely expanding fluids, with different material properties, evolving through the Israel-Stewart (IS) causal viscous hydrodynamics, and compare our results with those obtained in the relativistic Eckart-Landau-Navier-Stokes (ELNS) acausal viscous hydrodynamics. Through the analysis of scaling invariants we give a definition of thermalization time which can be self-consistently determined in viscous hydrodynamics. Next we construct the solutions for one-dimensional boost-invariant flows. Expansion of viscous fluids is slower than that of one-dimensional ideal fluids, resulting in entropy production. At late times, these flows are reasonably well approximated by solutions obtained in ELNS hydrodynamics. Estimates of initial energy densities from observed final values are strongly dependent on the dynamics one chooses. For the same material, and the same final state, IS hydrodynamics gives the smallest initial energy density. We also study fluctuations about these one-dimensional boost-invariant backgrounds; they are damped in ELNS hydrodynamics but can become sound waves in IS hydrodynamics. The difference is obvious in power spectra due to clear signals of wave-interference in IS hydrodynamics, which is completely absent in ELNS dynamics.

nucl-th↗
arXiv2006

Working Group Report: Heavy-Ion Physics and Quark-Gluon Plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of Quark-Gluon Plasma believed to have created in heavy-ion collisions and in early universe are reported.

hep-ph↗
arXiv2005

Elliptic flow and incomplete equilibration at RHIC

We argue that RHIC data, in particular those on the anisotropic flow coefficients v_2 and v_4, suggest that the matter produced in the early stages of nucleus-nucleus collisions is incompletely thermalized. We interpret the parameter (1/S)(dN/dy), where S is the transverse area of the collision zone and dN/dy the multiplicity density, as an indicator of the number of collisions per particle at the time when elliptic flow is established, and hence as a measure of the degree of equilibration. This number serves as a control parameter which can be varied experimentally by changing the system size, the centrality of the collision, or the beam energy. We provide predictions for Cu-Cu collisions at RHIC as well as for Pb-Pb collisions at the LHC.

nucl-th↗
arXiv2004

Strange Stars with a Density-Dependent Bag Parameter

We have studied strange quark stars in the framework of the MIT bag model, allowing the bag parameter B to depend on the density of the medium. We have also studied the effect of Cooper pairing among quarks, on the stellar structure. Comparison of these two effects shows that the former is generally more significant. We studied the resulting equation of state of the quark matter, stellar mass-radius relation, mass-central-density relation, radius-central-density relation, and the variation of the density as a function of the distance from the centre of the star. We found that the density-dependent B allows stars with larger masses and radii, due to stiffening of the equation of state. Interestingly, certain stellar configurations are found to be possible only if B depends on the density. We have also studied the effect of variation of the superconducting gap parameter on our results.

astro-ph↗
arXiv2003

Genuine collective flow from Lee-Yang zeroes

We propose to use the theory of phase transitions of Lee and Yang as a practical tool to analyze long-range correlations in a finite-size system. We apply it to the analysis of anisotropic flow in nucleus-nucleus collisions, and show that this method is more reliable than any other used so far.

nucl-th↗
arXiv2003

Analysis of anisotropic flow with Lee-Yang zeroes

We present a new method to extract anisotropic flow in heavy ion collisions from the genuine correlation among a large number of particles. Anisotropic flow is obtained from the zeroes in the complex plane of a generating function of azimuthal correlations, in close analogy with the theory of phase transitions by Lee and Yang. Flow is first estimated globally, i.e., averaged over the phase space covered by the detector, and then differentially, as a function of transverse momentum and rapidity for identified particles. The corresponding estimates are less biased by nonflow correlations than with any other method. The practical implementation of the method is rather straightforward. Furthermore, it automatically takes into account most corrections due to azimuthal anisotropies in the detector acceptance. The main limitation of the method is statistical errors, which can be significantly larger than with the ``standard'' method of flow analysis if the flow and/or the event multiplicities are too small. In practice, we expect this to be the most accurate method to analyze directed and elliptic flow in fixed-target heavy-ion collisions between 100 MeV and 10 GeV per nucleon (at the Darmstadt SIS synchrotron and the Brookhaven Alternating Gradient Synchrotron), and elliptic flow at ultrarelativistic energies (at the Brookhaven Relativistic Heavy Ion Collider, and the forthcoming Large Hadron Collider at CERN).

nucl-th↗
arXiv2002

Droplet Formation in Quark-Gluon Plasma at Low Temperatures and High Densities

Considering the low-temperature ($T$) and high-baryon-number-density ($n_B$) region of the QCD phase diagram, we present a model for the first-order phase transition between the quark-gluon plasma (QGP) and the recently proposed colour superconducting phase. We study nucleation of a droplet of the superconducting phase within the metastable QGP gas. Numerical results for the activation energy, radius and other physical parameters of the droplets, at various temperatures, densities and gap parameters, are given. We have estimated the latent heat of the phase transition. In the $T-n_B$ plane, we are able to demarcate the region of the superconducting phase.

hep-ph↗
arXiv2000

Is the Polarized Antiquark Sea in the Nucleon Flavor Symmetric?

We show that the model which naturally explains the $\bar u \ne \bar d$ asymmetry in the nucleon and is in quantitative agreement with the Gottfried sum rule data, also predicts that in the proton $Δ\bar u > 0 > Δ\bar s > Δ\bar d$ and $Δ\bar u - Δ\bar d > \bar d - \bar u > 0$. At the input scale, these results can be derived even analytically. Thus the violation of the flavor symmetry is more serious in the polarized case than in the unpolarized case. In contrast, many recent analyses of the polarized data have made a simplifying assumption that all the three $Δ\bar q$'s have the same sign and magnitude. We point out the need to redo these analyses, allowing for the alternate scenario as described above. We present predictions of the model for the $W^-$ asymmetry in polarized $pp$ scattering, which can be tested at RHIC; these are quite different from those available in the literature.

hep-ph↗
arXiv2000

Production and Equilibration of the Quark-Gluon Plasma with Chromoelectric Field and Minijets

Production and equilibration of quark-gluon plasma are studied within the color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic transport equations for quarks, antiquarks and gluons, are solved in the extended phase space which includes coordinates, momenta and color. Before the chromoelectric field is formed, hard and semihard partons are produced via minijets which provide the initial conditions necessary to solve the transport equations. The model predicts that in spite of the vast difference between the RHIC and LHC incident energies, once the local equilibrium is reached, the energy densities, the number densities and the temperatures at the two machines may not be very different from each other. The minijet input significantly alters the evolution of the deconfined matter, unless the color field is too strong. For the input parameters used here the equilibration time is estimated to be $\sim 1$ fm at RHIC and $\sim 0.5$ fm at LHC, measured from the instant when the two colliding nuclei have just passed through each other. The temperature at equilibration is found to be $\sim 250$ MeV at RHIC and $\sim 300$ MeV at LHC.

hep-ph↗
arXiv2000

Model for Polarized and Unpolarized Parton Density Functions in the Nucleon

We present a physical model for polarized and unpolarized structure functions and parton density functions (PDFs) of the proton and the neutron. It reproduces the data on F_2^p(x,Q^2) for 0.00001<x<1 and 2.5<Q^2<5000 GeV^2, F_2^p(x)-F_2^n(x), F_2^n(x)/F_2^p(x), xg(x), dbar(x)-ubar(x), d(x)/u(x), the Gottfried sum, the fractional momentum of charged partons and the polarized structure functions g_1^{p,n}(x), at various Q^2. We present for the first time, proton and neutron PDFs which do not assume charge symmetry. Contrary to the common practice, we explain polarized and unpolarized data with a single model.

hep-ph↗
arXiv1997

Using Drell-Yan Processes to Probe Nucleon and Meson Structure Functions

We investigate how Drell-Yan processes can be used to measure the magnitude of flavor symmetry violation in the proton sea. We examine the utility of the following beams: protons, charged pions, and charged kaons. In each case we present an approximate expression for the Drell-Yan asymmetry. Using currently available parton distributions, we locate those kinematic regions which provide the greatest information on the quantity $\bar{d}^p(x) - \bar{u}^p(x)$. If sufficiently intense $K^+$ beams were available, they could provide an efficient measurement of this quantity. Finally we present and discuss sets of sum rules for the Drell-Yan processes.

hep-ph↗
arXiv1997

New Source Term for QGP Formation in the Background-Field Model

We consider pair production in a space-time-dependent background field and derive a source term, i.e., production rate in the one-particle phase space. Such a source term is required in Boltzmann-equation-based models of quark-gluon plasma formation and evolution. We compare the source term derived here with the one that has been used in the literature so far. Significant differences are observed.

nucl-th↗
arXiv1997

phi-Meson Mass Modification in Heavy-Ion Collisions

We recently presented a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of $ϕ$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($ΔM$ and $ΔΓ$) of the $ϕ$ mesons when they are inside the dense matter formed in these collisions. We have now performed a Monte-Carlo simulation of this process. We illustrate our method with the help of available preliminary data. Extracted value of $ΔM$ is significantly larger than that obtained with an earlier method. Our results are consistent with the experimentally observed $p_T$ dependence of the mass shift.

hep-ph↗
arXiv1997

Apparent and Actual Shifts in Mass and Width of Phi Mesons Produced in Heavy-Ion Collisions

We present a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of $ϕ$ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width ($ΔM$ and $ΔΓ$) of the $ϕ$ mesons when they are inside the dense matter formed in these collisions. We illustrate our method with the help of available preliminary data. Extracted values of $ΔM$ and $ΔΓ$ are significantly larger than those obtained with an earlier method. Our results are consistent with the experimentally observed $p_T$ dependence of the mass shift. Finally, we present a phenomenological relation between $ΔM$ and $ΔΓ$. It provides a useful constraint on theories which predict the values of these two quantities.

hep-ph↗
arXiv1996

Statistical Model for the Nucleon Structure Functions

A phenomenological model for the nucleon structure functions is presented. Visualising the nucleon as a cavity filled with parton gas in equilibrium and parametrizing the effects due to the finiteness of the nucleon volume, we obtain a good fit to the data on the structure function $F_2^p$. The model then successfully predicts other unpolarized structure function data.

hep-ph↗
arXiv1995

Haldane Exclusion Statistics and the Boltzmann Equation

We generalize the collision term in the one-dimensional Boltzmann-Nordheim transport equation for quasiparticles that obey the Haldane exclusion statistics. For the equilibrium situation, this leads to the ``golden rule'' factor for quantum transitions. As an application of this, we calculate the density response function of a one-dimensional electron gas in a periodic potential, assuming that the particle-hole excitations are quasiparticles obeying the new statistics. We also calculate the relaxation time of a nuclear spin in a metal using the modified golden rule.

cond-mat↗