Browsing by Author "B.K. Patra"

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Baryon contrast ratio in an isentropic cosmological quark-hadron phase transition
(Elsevier, 1998) B.K. Patra; C.P. Singh
Assuming that the quark-hadron phase transition in the early Universe satisfies the Gibbs' construction for a first-order equilibrium phase transition with a further constraint of a continuous entropy per baryon-number ratio across the phase boundary, we show that the baryon contrast ratio R defined as a measure of the baryon-number density inhomogeneity across the phase interface, is independent of the critical temperature Tc for the phase transition. It does not depend on the QCD parameters as well. Our finding contradicts the earlier results. © 1998 Elsevier Science B.V. All rights reserved.
Baryon density inhomogeneity in a generalised mean field model
(Elsevier, 1997) B.K. Patra; C.P. Singh
A phenomenological mean field formalism developed to incorporate the excluded volume correction arising due to hard-core repulsion between baryons is used to calculate the isothermal baryon density fluctuation in the early universe arising due to a quark hadron phase transition. We notice that the values of the baryon density contrast ratio thus obtained differ much from those of either a pure excluded volume model or a pure mean field model when the critical temperature for the phase transition Tc ≥ 150 MeV.
Baryon number penetrability as a measure of isothermal baryon number fluctuations in the early universe
(Elsevier, 2000) B.K. Patra; V.J. Menon; C.P. Singh
We have examined the efficiency of the baryon-number transport mechanism across the phase boundary in a cosmological quark-hadron phase transition through the proper estimate of baryon-number penetrability 〈Σh〉. For this purpose we have derived first the double-pair creation probability Pb in terms of single-pair creation probability per unit time and unit volume Km and then obtained an analytical expression for 〈Σh〉. Our calculation is free from the uncertainty of the value of double-pair creation probability per unit time and unit volume Kb which was used as the free parameter in earlier calculations. Finally the variations of double-pair creation probability Pb as well as 〈Σn〉 with temperature are shown and compared with other known results. © 2000 Elsevier Science B.V. All rights reserved.
Baryon-number density in hadronic gas models and baryon asymmetry in the early Universe
(1996) B.K. Patra; K.K. Singh; S. Uddin; C.P. Singh
We have recently shown that the inclusion of finite-size volume corrections for the hadrons in the hadronic gas phase drastically alters the conclusions regarding isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe. In this paper we compare in detail the predictions of various existing thermodynamically consistent hadron gas (HG) models for the baryon density in the HG phase and its dependence on the temperature in order to draw a firm conclusion regarding the results obtained in the earlier paper. © 1996 The American Physical Society.
Baryon-number fluctuations in a quark-hadron phase transition
(1994) C.P. Singh; B.K. Patra; Saeed Uddin
Isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe are obtained by including the quark-gluon interactions up to the order gs3 in the perturbative QCD coupling constant in the quark-gluon plasma (QGP) phase and the finite-size volume corrections for the hadrons in the hadron-resonance gas (HRG) and their effects on the primordial nucleosynthesis (PNS) are analyzed. The ratio of the baryon-number densities in the QGP and HRG phases at the critical temperature Tc is larger than one in the range 150 MeV
EOS for a QGP with a temperature and baryon chemical potential dependent bag pressure
(Springer Verlag, 1997) B.K. Patra; C.P. Singh
We develop an equation of state (EOS) for the quark-gluon plasma (QGP) involving the temperature and baryon chemical potential dependent bag pressure arising due to the entropy and baryon number conservation at the phase boundary together with the Gibbs' construction for an equilibrium phase transition. We show that the bag pressure thus obtained yields a decreasing behaviour with the increasing baryon chemical potential at a fixed temperature. Further consequences of the modified bag pressure are discussed. © Springer-Verlag 1997.
Gauss law constraints on Debye-Hückel screening
(2007) Ritesh Kumar Dubey; V.J. Menon; Madhukar Mishra; Mukesh Kumar Pandey; B.K. Patra
We demand that the Gauss law at the edge must be obeyed by the electric potential Φ(r) generated within a neutral plasma/electrolyte of strictly finite size by the introduction of a test charge qb. Our proposal has the nice features that total ionic numbers are conserved, the point-Coulomb behaviour of Φ(r) is guaranteed at short-distance, and accumulation of induced charges near the centre and the surface can be demonstrated rigorously. In contrast, the standard Debye-Hückel potential ΦD(r) applicable to unbounded plasma has the strange features that the Gauss law cannot be obeyed at the plasma's edge, total ionic numbers themselves are altered, the short-distance Coulomb behaviour has to be imposed by hand, and induced charge appearance at the surface cannot be built-in. © Indian Academy of Sciences.
Isentropic quark hadron phase boundary and strangeness enhancement
(World Scientific Publishing Co. Pte Ltd, 2000) B.K. Patra; C.P. Singh; F.C. Khanna
We develop a phenomenological equation of state for the quark-gluon plasma containing η(f) flavors when the entropy per baryon ratio remains continuous across the phase boundary and thus derive a generalized expression for the temperature and baryon chemical potential dependent bag constant. The phase boundaries are obtained for an isentropic quark-hadron phase transition after using Gibbs' criteria and the transition to an ideal QGP from the solution of the condition B(μ, T) = 0. The variation of critical temperature T(c) with η(f) and the temperature variation of the quantity (ε - 4P)/T4 which measures the interaction present in QGP are obtained and compared with the results from lattice calculations. Finally we obtain the strange particle ratios on the two phase boundaries which will be useful in identifying deconfined and/or ideal QGP formation in the heavy-ion experiments.
J/ψ gluonic dissociation revisited: I. Fugacity, flux and formation time effects
(2004) B.K. Patra; V.J. Menon
We revisit the standard treatment due to Xu et al. of J/ψ suppression due to gluonic bombardment in an equilibrating quark-gluon plasma. Effects arising from gluon fugacity, relative g- ψ flux, and ψ meson formation time are explicitly incorporated in the formulation of the gluon number density, velocity-weighted cross section, and the survival probability. Our new formulae are applied to a numerical study of the pattern of J/ψ suppression in the central rapidity region at RHIC/LHC energies. The temperature and transverse momentum dependence of our graphs have noticeable differences from those of Xu et al. © Springer-Verlag / Societa Italiana di Fisica 20004.
J/ψ gluonic dissociation revisited: II. Hydrodynamic expansion effects
(2005) B.K. Patra; V.J. Menon
We explicitly take into account the effect of the hydrodynamic expansion profile on the gluonic break-up of the J/\ψ's produced in an equilibrating parton plasma. Attention is paid to the space-time inhomogeneities as well as Lorentz frames while deriving new expressions for the gluon number density n g , the average dissociation rate 〈Γ̃〉, and the survival probability of J\ψ, S. A novel type of partial wave interference mechanism is found to operate in the formula of 〈Γ̃〉. A non-relativistic longitudinal expansion from the small length of the initial cylinder is found to push the S(p T) graph above the no flow case considered by us earlier [9]. However, the relativistic flow corresponding to the large length of the initial cylinder pushes the curve of S(p T) downwards at LHC but upwards at RHIC. This mutually different effect on S(p T) may be attributed to the different initial temperatures generated at LHC and RHIC. © Springer-Verlag.
J/ψ gluonic dissociation revisited: III. Effects of transverse hydrodynamic flow
(2006) B.K. Patra; V.J. Menon
In a recent paper [B.K. Patra, V.J. Menon, Eur. Phys. J. C 44, 567 (2005)] we developed a very general formulation to take into account explicitly the effects of the hydrodynamic flow profile on the gluonic breakup of J/ψs produced in an equilibrating quark-gluon plasma. Here we apply that formulation to the case when the medium is undergoing a cylindrically symmetric transverse expansion starting from RHIC or LHC initial conditions. Our algebraic and numerical estimates demonstrate that the transverse expansion causes enhancement of the local gluon number density ng, affects the p T-dependence of the average dissociation rate 〈Γ̃ 〉 through a partial-wave interference mechanism and makes the survival probability S(pT) to change with pT very slowly. Compared to the previous case of a longitudinal expansion the new graph of S(p T) is pushed up at LHC but develops a rich structure at RHIC, due to a competition between the transverse catch-up time and the plasma lifetime. © Springer-Verlag Berlin Heidelberg 2006.
Langevin dynamics of J/ψ in a parton plasma
(2002) B.K. Patra; V.J. Menon
We consider the Brownian motion of a cc̄ pair produced in the very early stage of a quark-gluon plasma. The one-dimensional Langevin equation is solved formally to get purely mechanical properties at small and large times. Stochastically-averaged variances are examined to extract the time scales associated with swelling and ionization of the bound state. Simple numerical estimates of the time scales are compared with other mechanisms of J/ψ suppression. © 2002 Published by Elsevier Science B.V.
Momentum-energy change in elastic relativistic binary collisions
(2009) V.J. Menon; R.K. Dubey; M. Mishra; B.K. Patra
We consider a relativistic elastic collision between a projectile of momentum p with a target atom of momentum k in a general inertial frame. We employ one space plus one time Minkowski geometry and calculate the momentum transfer vector qμ suffered by the projectile calculated via a Lorentz transformation to the barycentric frame and then eliminate k. The resulting expression for qμ reproduces several known cases, its algebraic behavior can be interpreted physically, and it leads to a simple understanding of the relativistic equipartition law. © 2009 American Association of Physics Teachers.
Non-orthogonality of Lippmann-Schwinger-Low states
(2004) V.J. Menon; B.K. Patra; Ritesh Kumar Dubey
For the general short-ranged potential the Lippmann-Schwinger-Low (LSL) scattering formalism by taking the limit ε → +0 at the end of the analysis, with ε being an infinitesimal adiabatic parameter has been re-examined. It is found that the LSL state |ψ k L〉 does not strictly satisfy the Schrodinger eigen equation, and the pair |ψ n L〉,|ψ k L〉 is mutually non-orthogonal if E n = E k, n ≠ k. For this purpose a new type of projection operator η k o, a non-linear relation among transition amplitudes, and a separable interaction as illustration have been used.
Temperature and baryon-chemical-potential-dependent bag pressure for a deconfining phase transition
(1996) B.K. Patra; C.P. Singh
We explore the consequences of a bag model developed by Leonidov et al. for the deconfining phase transition in which the bag pressure is made to depend on the temperature and baryon chemical potential in order to ensure the entropy and baryon number conservation at the phase boundary together with the Gibbs construction for an equilibrium phase transition. We show that the bag pressure thus obtained yields an anomalous increasing behavior with the increasing baryon chemical potential at a fixed temperature which defies a physical interpretation. We demonstrate that the inclusion of the perturbative interactions in the QGP phase removes this difficulty. Further consequences of the modified bag pressure are discussed. © 1996 The American Physical Society.
Thermodynamically consistent EOS for hot dense hadron gas
(Elsevier, 1996) C.P. Singh; B.K. Patra; K.K. Singh
We propose an alternative form of a thermodynamically consistent equation of state (EOS) incorporating the Van der Waals type of excluded volume effect for a hot and dense hadronic gas consisting of many species of finite-size baryons is obtained. We compare its predictions in detail with those of the other thermodynamically consistent as well as inconsistent models.