arXiv subjects

R. V. Gavai

Publications and source records attributed to R. V. Gavai.

36 records · Page 2Linked to original sources

arXiv2000

Heavy ion physics : theory

Lattice quantum chromodynamics (QCD) predicts a new state of matter, called quark-gluon plasma (QGP), at sufficiently high temperatures or equivalently large energy densities. Relativistic heavy ion collisions are expected to produce such energy densities, thereby providing us a chance to test the above prediction. After a brief introduction of the necessary theoretical concepts, I present some critical comments on the experimental results with an aim to examine whether QGP has already been observed experimentally.

hep-ph↗

arXiv2000

Fermions obstruct dimensional reduction in hot QCD

We have studied, for the first time, screening masses obtained from glueball-like correlators in Quantum Chromodynamics with four light dynamical flavours of quarks in the temperature range 1.5T_c < T < 3T_c, where T_c is the temperature at which the chiral transition occurs. We have also studied pion-like and sigma-like screening masses, and found that they are degenerate in the entire range of T. These obstruct perturbative dimensional reduction since the lowest glueball screening mass is heavier than them. Extrapolation of our results suggests that this obstruction may affect the entire range of temperature expected to be reached even at the Large Hadron Collider.

hep-lat↗

arXiv2000

QCD Working Group Report

This is the report of the QCD working group at WHEPP 6. Discussions and work on heavy ion collisions, polarised scattering, and collider phenomenology are reported.

hep-ph↗

arXiv2000

Quark-Gluon Plasma: Status of Heavy Ion Physics

Lattice quantum chromodynamics (QCD), defined on a discrete space time lattice, leads to a spectacular non-perturbative prediction of a new state of matter, called quark-gluon plasma (QGP), at sufficiently high temperatures or equivalently large energy densities. The experimental programs of CERN, Geneva and BNL, New York of relativistic heavy ion collisions are expected to produce such energy densities, thereby providing us a chance to test the above prediction. After a brief introduction of the necessary theoretical concepts, I will present a critical review of the experimental results already obtained by the various experiments in order to examine whether QGP has already been observed by them.

hep-ph↗

arXiv1999

Z2 Monopoles, Vortices, and the Deconfinement Transition in Mixed Action SU(2) Gauge Theory

Adding separate chemical potentials lambda and gamma for Z2 monopoles and vortices respectively in the Villain form of the mixed fundamental-adjoint action for the SU(2) lattice gauge theory, we investigate their role in the interplay between the deconfinement and bulk phase transitions using Monte Carlo techniques. Setting lambda to be nonzero, we find that the line of deconfinement transitions is shifted in the coupling plane but it behaves curiously also like the bulk transition line for large enough adjoint coupling, as for lambda=0. In a narrow range of couplings, however, we find separate deconfinement and bulk phase transitions on the same lattice for nonzero and large lambda, suggesting the two to be indeed coincident in the region where a first order deconfinement phase transition is seen. In the limit of large lambda and gamma, we obtain only lines of second order deconfinement phase transitions, as expected from universality.

hep-lat↗

arXiv1999

Probing the quark-gluon plasma with a new Fermionic correlator

We present the first measurement of a new correlation function of Fermion bilinears in finite temperature QCD with and without dynamical quarks in a quantum number channel in which non-trivial correlations are known to be present for purely gluonic operators. We find that the Fermion correlator vanishes for $T \ge 3T_c/2$, in agreement with the expectation for weakly interacting quarks in a quark-gluon plasma.

hep-lat↗

arXiv1999

Impact of Z_2 monopoles and vortices on the deconfinement transition

The impact of Z_2-monopoles and vortices on the bulk and the deconfinement phase transitions of the SU(2) lattice gauge theory with a mixed Villain form of action is investigated by varying their numbers with appropriate chemical potentials. Suppressing the former shifts the line of deconfinement transitions in the coupling plane but it continues to behave also like the bulk transition line. We find separate deconfinement and bulk phase transitions on the same lattice, suggesting the two to be indeed coincident at higher adjoint couplings. Universality is restored when both monopoles and vortices are suppressed.

hep-lat↗

arXiv1999

The Deconfinement Transition in SO(3) Gauge Theory

The SO(3) lattice gauge theory with a Villain form of action was investigated by Monte Carlo techniques on asymmetric lattices with Nt = 2 and 4, where Nt is the number of sites in the temporal extent. Unlike the results for higher Nt, only one transition of second order was found for Nt = 2 . An extended action with an irrelevant term to suppress Z_2 monopoles enabled us to get a better view of the deconfinement transition as the effects of bulk transition could be suppressed as well. Although the action has no global Z_2 symmetry for the SO(3) theory, unlike the SU(2) theory at finite temperature, our study revealed a second order deconfinement transition, with properties similar to the deconfinement transition of SU(2).

hep-lat↗

arXiv1997

Is there Anomalous J/psi Suppression in Present-day Heavy-ion Collisions?

We re-analyse the data on J/psi cross sections for proton-nucleus and nucleus-nucleus collisions obtained by the CERN experiments NA38, NA51 and NA50. Our systematic analysis of error propagation shows that the no anomalous suppression of J/psi in Pb-Pb collisions can be substantiated at 95% confidence limit. The significance of the NA50 result would be enhanced by more precise p-A data on J/psi cross sections.

hep-ph↗

arXiv1994

Heavy Quark Production in pp Collisions

A systematic study of the inclusive single heavy quark and heavy-quark pair production cross sections in pp collisions is presented for RHIC and LHC energies. We compare with existing data when possible. The dependence of the rates on the renormalization and factorization scales is discussed. Predictions of the cross sections are given for two different sets of parton distribution functions.

hep-ph↗

arXiv1994

High Precision $J/ψ$ and $Υ$-production data and the Nuclear Glue

We use the high statistics E-772 data on the nuclear dependence of the production of quarkonia $(J/ψ$ and $Υ)$ and dimuons at large transverse momentum $(p_T)$ in $p$-$A$ collisions to get information about the gluonic EMC effect. We find a satisfactory quantitative agreement of the theoretical predictions with the data although none of the models of the EMC effect we consider could account for the entire data. Since all the qualitative features are understood none the less in terms of perturbative QCD with nuclear dependent parton densities, our results suggest that these data can now be used for a better determination of the nuclear parton densities. Our conslusions are shown to be insensitive to the hadronisation mechanism for the quarkonia.

hep-ph↗

arXiv1993

C-Periodicity and the Physical Mass in the 3-State Potts Model

The standard infinite-volume definition of connected correlation function and particle mass in the 3-state Potts model can be implemented in Monte Carlo simulations by using C-periodic spatial boundary conditions. This avoids both the breaking of translation invariance (cold wall b.c.) and the phase-dependent and thus possibly biased evaluation of data (periodic boundary cconditions). The numerical feasibility of the standard definitions is demonstrated by sample computations on a 24*24*48 lattice.

hep-lat↗

arXiv1993

Supercooling and Nucleation in Phase Transitions of the Early Universe -

The three phase transitions - the GUT, the electro-weak and the quark-hadron, which the universe is assumed to have undergone produce very important physical effects if they are assumed to be of first order. It is also important that enough supercooling is produced at these transitions so that the rate of nucleation of the lower temperature phase out of the higher temperature phase is large. We argue on the basis of finite-size scaling theory that for the quark-hadron and the electro-weak transitions the universe does nor supercool enough to produce sizeable nucleation rates. Only for the GUT transition nucleation probability seems to be significant.

astro-ph↗

arXiv1993

Sizing up the Nuclear Glue in $J/ψ$-production

Nuclear gluon densities are of great importance to the physics of relativistic heavy ion collisions, in particular, in assessing the origin of $J/ψ$-suppression. We describe our attempts to distinguish various models of the gluonic EMC-effect, using the existing $J/ψ$-production data in proton-nucleus collisions. We find that no model is capable of explaining {\em all} the features of the high precision E772 data although the overall trend suggests this to be more a matter of fine-tuning the models than the presence of new physical effects.

hep-ph↗

arXiv1992

Looking for the gluonic EMC effect in associated $J/ψ$ + $γ$ production

We study the associated production of $ J/ψ + γ$ in fixed-target experiments with nuclear targets as well as at the relativistic heavy-ion collider (RHIC). We find that this process affords a very clean probe of $ρ_g$, the ratio of gluon density in a heavy nucleus to that of a proton. The combined $x$ range thus available can be used to discriminate between the predictions of different models of the EMC effect for $ρ_g$.

hep-ph↗

arXiv1992

A Lower Bound on $T_{SR}/{m_{\rm H}}$ in the O(4) Model on Anisotropic Lattices

Results of an investigation of the $O(4)$ spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy $ξ$. From the numerical simulations we obtain a lower bound of $T_{\rm SR} / m_{\rm H} \simeq 0.58 \pm 0.02$ at a value for the Higgs mass $m_{\rm H}a_s \simeq 0.5$, which is lowered further by about $10\%$ at $m_{\rm H}a_s \simeq 1$. Requiring certain timelike correlation functions to coincide with their spacelike counterparts, quantum and scaling corrections to the anisotropy are determined and are found to be small, i.e., the anisotropy is found to be close to the ratio of spacelike and timelike lattice spacings.

hep-lat↗

arXiv1992

Can the Quark-Gluon Plasma in the Early Universe be supercooled?

The quark-hadron phase transition in the early universe can produce inhomogeneities in the distribution of nucleons, which in turn affect the primordial nucleosynthesis. In all the investigations of this problem it has been assumed that the degree of supercooling of the quark-gluon plasma after the phase transition is large enough to produce a significant rate of nucleation of hadrons. Using the latest results of finite temperature lattice QCD and the finite size scaling theory, we argue that the degree of supercooling is in fact extremely small and hence the nucleation rate is negligible.

astro-ph↗

arXiv1992

A Study of Symmetry Restoration at Finite Temperature in the O(4) Model Using Anisotropic Lattices

Results of investigations of the O(4) spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and the numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy. We obtain a lower bound of $0.59 \pm 0.04$ for the ratio, $T_{\rm SR}/m_{\rm H}$, at $m_{\rm H}a \simeq 0.5$, which is lowered further by about 10% at $m_{\rm H}a \simeq 1.$

hep-lat↗