arXiv subjects
Publications and source records attributed to Rajiv V. Gavai.
We report the first investigation of the QCD transition temperature, T_c, for two flavours of staggered quarks with unequal masses at lattice spacings of 1/4T. On changing the u/d quark mass ratio in such a way that m(pi_0)^2/m(pi_+)^2 changes from 1 to 0.78, thus bracketing the physical value of this ratio, we find that T_c remains unchanged in units of both m_rho and Lambda_MSbar.
The deconfinement transition in SU(4) lattice gauge theory is investigated on N_s^3 X N_t lattices for N_s = 8-16 and N_t = 4-8 using a modified Wilson action which is expected to be free of any bulk transitions. The susceptibility chi_{|L|}^{max}, where L is the order parameter for deconfinement, is found to increase linearly with spatial volume for N_t = 4, 5, and 6, indicating a first order deconfinement phase transition. The latent heat of the transition is estimated to be approximately 2/3 of the corresponding ideal gas energy density at T_c.
We report the continuum limit of quark number susceptibilities in quenched QCD. Deviations from ideal gas behaviour at temperature T increase as the lattice spacing is decreased from T/4 to T/6, but a further decrease seems to have very little effect. The measured susceptibilities are 20% lower than the ideal gas values, and also 10% below the hard thermal loop (HTL) results. The off-diagonal susceptibility is several orders of magnitude smaller than the HTL results. We verify a strong correlation between the lowest screening mass and the susceptibility. We also show that the quark number susceptibilities give a reasonable account of the Wroblewski parameter, which measures the strangeness yield in a heavy-ion collision.
Results from our recent investigations of quark number susceptibilities in both quenched and 2-flavour QCD are presented as a function of valence quark mass and temperature. A strong reduction (approx. 40%) is seen in the strange quark susceptibility above T_c in both the cases. A comparison of our isospin susceptibility results with the corresponding weak coupling expansion reveals once again the non-perturbative nature of the plasma up to 3T_c. Evidence relating the susceptibility to another non-perturbative phenomena, pionic screening lengths, is presented.
Results from our recent investigations of quark number susceptibilities in both quenched and 2-flavour QCD are presented as a function of valence quark mass and temperature. A strong reduction (~40%) is seen in the strange quark susceptibility above Tc in both cases. A comparison of our isospin susceptibility results with the corresponding weak coupling expansion reveals once again the non-perturbative nature of the plasma up to 3 Tc. Evidence relating the susceptibility to another non-perturbative phenomena, pionic screening lengths, is presented.
The deconfinement transition in SU(4) lattice gauge theory is studied on N_s^3 X N_t lattices with N_s = 8-16 and N_t = 4-8 using a modified Wilson action which is expected to have no bulk transitions. The peak of susceptibility χ_{|L|} is found to increase linearly with spatial volume for N_t = 4, 5, and 6, indicating a first order deconfinement phase transition. The latent heat is estimated to be approximately 2/3 of the corresponding ideal gas energy density at T_c.
We studied QCD with two flavors of dynamical staggered quarks at finite temperature, with a bare sea quark mass of about 17 MeV. We report investigations of baryon, isospin, charge and strangeness susceptibilities, as well as screening masses obtained from correlators of local and one-link separated meson operators. These were studied as functions of valence quark mass at several temperatures. Our results for susceptibilities deviate significantly from ideal gas values, and even more from the weak coupling series. We also report the first measurement of off-diagonal quark number susceptibilities below the transition temperature, Tc, where they are the main contribution to charge fluctuations. We present evidence for a close connection between the susceptibilities and the screening masses.
We study physics at temperatures just above the QCD phase transition (Tc) using chiral (overlap) Fermions in the quenched approximation of lattice QCD. Exact zero modes of the overlap Dirac operator are localized and their frequency of occurrence drops with temperature. This is closely related to axial U(1) symmetry, which remains broken up to 2Tc. After subtracting the effects of these zero modes, chiral symmetry is restored, as indicated by the behavior of the chiral condensate. The pseudoscalar and vector screening masses are close to ideal gas values.
We report first results on the strange quark number susceptibility, chi_s, over a large range of temperatures, mainly in the plasma phase of QCD. Chi_s jumps across the phase transition temperature, T_c, and grows rapidly with temperature above but close to T_c. For all quark masses and susceptibilities in the entire temperature range studied, we found significant departures from ideal-gas values. We also observed a strong correlation between these quantities and the susceptibility in the scalar/pseudo-scalar channel, supporting ideas of ``dynamical confinement'' in the high temperature phase of the QCD plasma.
Suppressing monopoles and vortices by introducing large chemical potentials for them in the Wilson action for the SU(2) lattice gauge theory, we study the nature of the deconfinement phase transition on N_sigma^3 X N_tau lattices for N_tau =4, 5, 6 and 8 and N_sigma = 8-16. Using finite size scaling theory, we obtain ω= 1.93 +/- 0.03 for N_tau = 4, in excellent agreement with universality. The critical couplings for N_tau= 4, 5, 6 and 8 lattices exhibit large shifts towards the strong coupling region when compared with the usual Wilson action, and suggest a lot smoother approach to scaling.
Suppressing monopoles and vortices by introducing large chemical potentials for them in the Wilson action for the SU(2) lattice gauge theory, we study the nature of the deconfinement phase transition on N_σ^3 \times N_τlattices for N_τ= 4, 5, 6 and 8 and N_σ= 8--16. Using finite size scaling theory, we obtain ω= 1.93 \pm 0.03 for N_τ= 4, in excellent agreement with universality. Corresponding determinations for the N_τ= 5 and 6 lattices are also found to be in very good agreement with this estimate. The critical couplings for N_τ= 4, 5, 6 and 8 lattices exhibit large shifts towards the strong coupling region when compared with the usual Wilson action, and suggest a lot smoother approach to scaling.
The paper has been withdrawn
We investigate the effect of $Z_2$ magnetic monopoles and vortices on the finite temperature deconfinement phase transition in the fundamental - adjoint SU(2) lattice gauge theory. In the limit of complete suppression of the $Z_2$ monopoles, the mixed action for the SU(2) theory in its Villain form is shown to be self-dual under the exchange of the fundamental and adjoint couplings. By further suppressing the $Z_2$ vortices we show that the extended model reduces to the Wilson action with a modified coupling. The universality of the SU(2) deconfinement phase transition with the Ising model is therefore expected to remain intact in the entire plane of the fundamental-adjoint couplings in the continuum limit. The self-duality arguments related to the suppression of $Z_2$ monopoles are also applicable to the Villain form of mixed action for the SU(N) theory with $Z_{N}$ magnetic monopoles.
The phase diagram of SO(3) lattice gauge theory is investigated by Monte Carlo techniques on both symmetric and asymmetric lattices with a view (i) to understanding the relationship between the bulk transition and the deconfinement transition, and (ii) to resolving the current ambiguity about the nature of the high temperature phase. A number of tests, including an introduction of a magnetic field and measurement of different correlation functions in the phases with positive and negative values for the adjoint Polyakov line, lead to the conclusion that the two phases correspond to the same physical state. Studies on lattices of different sizes reveal only one phase transition for this theory on all of them and it appears to have a deconfining nature.
A systematic analysis of the L-dependence of the J/psi-suppression in the data of the CERN NA38 and NA50 experiments shows that the anomalous suppression in the 1995 Pb-Pb data is at best a 4$σ$ effect at any of the L-values for the Pb-Pb data, where L is the geometrical mean path length of the J/psi in the colliding nuclei. Possible implications for the 1996 data are discussed.
The phase diagram of SO(3) lattice gauge theory at finite temperature is investigated by Monte Carlo techniques with a view i) to understand the relationship between the deconfinement phase transitions in the SU(2) and SO(3) lattice gauge theories and ii) to resolve the current ambiguity of the nature of the high temperature phases of the latter. Phases with positive and negative adjoint Polyakov loop are shown to have the same physics. A first order deconfining phase transition is found for N_t=4.
We examine certain issues related to the universality of the SU(2) lattice gauge theory at non-zero temperatures. Using Monte Carlo simulations and strong coupling expansions, we study the behavior of the deconfinement transition in an extended coupling plane (beta, beta_A) around the tricritical point where the deconfinement transition changes from second to first order. Our numerical results on N_tau =2,4,6,8 lattices show that the tricritical point first moves down towards the Wilson axis and and then moves slowly upwards, if at all, as the lattice spacing is reduced. Lattices with very large N_tau seem to be therefore necessary for the mixed action to exhibit the critical exponents of the three dimensional Ising model for positive values of the adjoint coupling.
Using improved mean field and strong coupling expansions we re-analyse the bulk phase diagram of the fundamental-adjoint action of the SU(2) Lattice Gauge Theory. We find that the qualitative features of the bulk phase diagram are robust and unchanged by the inclusion of higher order terms. On the other hand, some of the quantitative features, such as the location of the endpoint of the line of bulk phase transitions, seem to be strongly dependent on the higher terms of the strong coupling expansion.