QCD Critical Point: The Race is On

A critical point in the phase diagram of Quantum Chromodynamics (QCD), if established either theoretically or experimentally, would be as profound a discovery as the good-old gas-liquid critical point. Unlike the latter, however, first-principles based approaches are being employed to locate it theoretically. Due to the short lived nature of the concerned phases, novel experimental techniques are needed to search for it. The Relativistic Heavy Ion Collider (RHIC) in USA has an experimental program to do so. This short review is an attempt to provide a glimpse of the race between the theorists and the experimentalists as well as that of the synergy between them.Comment: 15 Pages, Invited Review for Praman

Phase Diagram of SO(3) Lattice Gauge Theory at Finite Temperature

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.Comment: 3 pages, 2 figures, latex2e, uses espcrc2.sty. Contribution to Lattice '97, Edinburgh, July 1997, to appear in Nucl. Phys. B (Proc. Suppl.) Latex command for figures correcte

Improving the Quark Number Susceptibilities for Staggered Fermions

Quark number susceptibilities approach their ideal gas limit at sufficiently high temperatures. As in the case of other thermodynamic quantities, this limit itself is altered substantially on lattices with small temporal extent, N_t = 4-8, making it thus difficult to check the validity of perturbation theory. Unlike other observables, improving susceptibilities or number densities is subject to constraints of current conservation and absence of chemical potential dependent divergences. We construct such an improved number density and susceptibility for staggered fermions and show that they approximate the continuum ideal gas limit better on small temporal lattices.Comment: Lattice2002(nonzerot), 3 pages, 3 figure

The Wroblewski Parameter from Lattice QCD

Enhancement of strangeness production has since long been proposed as a promising signal of quark-gluon plasma production. A convenient indicator for it is the Wroblewski parameter which has been shown to be about a factor two higher in heavy ion collisions. Using a method proposed by us earlier, we obtained lattice QCD results for the Wroblewski parameter from our simulations of QCD with two light quarks both below and above the chiral transition. Our first principles based and parameter free result compare well with the A-A data.Comment: 5 pages, 5 figures, To appear in the proceedings of the seventeenth international conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, US

Quark Number Susceptibilities & The Wroblewski Parameter

The Wroblewski parameter is a convenient indicator of strangeness production and can be employed to monitor a signal of quark-gluon plasma production : enhancement of strangeness production. It has been shown to be about a factor two higher in heavy ion collisions than in hadronic collisions. Using a method proposed by us earlier, we obtained lattice QCD results for the Wroblewski parameter from our simulations of QCD with two light quarks both below and above the chiral transition. Our first principles based and parameter free result compare well with the A-A data from SPS and RHIC.Comment: 5 pages, Plenary talk by R.V.G. at Hard Probes 2004, Ericeira, Portugal, Nov.4-10, 2004; Reference adde

Z_2 Monopoles, Vortices and the Universality of the SU(2) Deconfinement Transition

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.Comment: 12 pages, Latex, To appear in Phys. Lett.

More On The SU(2) Deconfinement Transition In The Mixed Action

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.Comment: LaTeX, 35 Pages including 8 Postscript Figures, Final version to be published in Phys. Rev. D, Title changed in the journal, Additional results on larger lattices presented which change somewhat our earlier conclusions. Added a reference and 4 figure

Anomaly at finite density and chiral fermions on lattice

Using both perturbation theory in the Euclidean formalism as well as the non-perturbative Fujikawa's method, we verify that the chiral anomaly equation remains unaffected in continuum QCD in the presence of nonzero chemical potential, \mu. We extend our considerations to lattice fermions with exact chiral symmetry and discuss the consequences for the recent Bloch-Wettig proposal for the Dirac operator at finite chemical potential. We propose a new simpler method of incorporating \mu.Comment: Talk presented at the XXVII International Symposium on Lattice Field Theory, July 26-31, 2009, Peking University, Beijing, China; 7 pages, 3 figure

Results from Lattice QCD

I present our recent results on the critical end point in the \mu_B-T phase diagram of QCD with two flavours of light dynamical quarks and compare them with similar results from other groups. Implications for a possible energy scan at the RHIC are discussed. I also comment briefly on the new results of great relevance to heavy ion collisions from finite temperature lattice QCD simulations on speed of sound, specific heat and on the fate of J/\psi.Comment: Invited Plenary Talk given at 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, Kolkata, India, February 8-12, 2005; LaTeX in Journal of Physics G style; 9 pages including figure