Sequential Quarkonium Suppression

We use recent lattice data on the heavy quark potential in order to determine the dissociation temperatures of different quarkonium states in hot strongly interacting matter. Our analysis shows in particular that certain quarkonium states dissociate below the deconfinement point.Comment: Talk presented on the International Workshop on the Physics of the Quark - Gluon Plasma, September 4-7, 2001, Palaisea

Deconfinement through Chiral Symmetry Restoration in Two-Flavour QCD

We propose that in QCD with dynamical quarks, colour deconfinement occurs when an external field induced by the chiral condensate strongly aligns the Polyakov loop. This effect sets in at the chiral symmetry restoration temperature T-chi and thus makes deconfinement and chiral symmetry restoration coincide. The predicted singular behaviour of Polyakov loop susceptibilities at T-chi is shown to be supported by finite temperature lattice calculations.Comment: 7 pages, 6 figure

Quarkonium Feed-Down and Sequential Suppression

About 40-50 % of the quarkonium ground states J/psi(1S) and Upsilon(1S) produced in hadronic collisions originate from the decay of higher excitations. In a hot medium, these higher states are dissociated at lower temperatures than the more tightly bound ground states, leading to a sequential suppression pattern. Using new finite temperature lattice results, we specify the in-medium potential between heavy quarks and determine the dissociation points of different quarkonium states. On the basis of recent CDF data on bottomonium production, we then obtain first predictions for sequential Upsilon suppression in nuclear collisions.Comment: 19 pages, LaTeX, 11 figure

Dynamical Restoration of Z_N Symmetry in SU(N)+Higgs Theories

We study the Z_N symmetry in SU(N)+Higgs theories with the Higgs field in the fundamental representation. The distributions of the Polyakov loop show that the Z_N symmetry is explicitly broken in the Higgs phase. On the other hand, inside the Higgs symmetric phase the Polyakov loop distributions and other physical observables exhibit the Z_N symmetry. This effective restoration of the Z_N symmetry changes the nature of the confinement-deconfinenement transition. We argue that the Z_N symmetry will lead to time independent topological defect solutions in the Higgs symmetric deconfined phase which will play important role at high temperatures.Comment: 13 pages, 4 figure

Stabilisation of Seven Directions in an Early Universe M -- theory Model

Our model consists of intersecting 22'55' branes in M theory distributed uniformly in the common transverse space. Equations of state follow from U duality symmetries. In this model, three spatial directions expand, and seven directions stabilise to constant sizes. From string theory perspective, the dilaton is hence stabilised. The constant sizes depend on certain imbalance among initial values. One naturally obtains M_{11} \simeq M_s \simeq M_4 and g_s \simeq 1 within a few orders of magnitude. Smaller numbers, for example M_s \simeq 10^{- 16} M_4, are also possible but require fine tuning.Comment: 11 Pagesl. Latex file. Version 2: Minor changes and a reference added. Version 3: Title changed; many textual modifications, mainly to keep within journal's length constraints, and to explain the differences between brane gas models and intersecting brane configurations used here; references added. To appear in Physical Review D (Rapid communications

Resonant Production of Topological Defects

We describe a novel phenomenon in which vortices are produced due to resonant oscillations of a scalar field which is driven by a periodically varying temperature T, with T remaining much below the critical temperature $T_c$. Also, in a rapid heating of a localized region to a temperature {\it below} $T_c$, far separated vortex and antivortex can form. We compare our results with recent models of defect production during reheating after inflation. We also discuss possible experimental tests of our predictions of topological defect production {\it without} ever going through a phase transition.Comment: Revtex, 13 pages including 5 postscript figure

Vortex-Antivortex Pair Production in a First Order Phase Transition

We carry out numerical simulation of a first order phase transition in 2+1 dimensions by randomly nucleating bubbles, and study the formation of global U(1) vortices. Bubbles grow and coalesce and vortices are formed at junctions of bubbles via standard Kibble mechanism as well as due to a new mechanism, recently proposed by us, where defect-antidefect pairs are produced due to field oscillations. We make a comparative study of the contribution of both of these mechanisms for vortex production. We find that, for high nucleation rate of bubbles, vortex-antivortex pairs produced via the new mechanism have overlapping configurations, and annihilate quickly; so only those vortices survive till late which are produced via the Kibble mechanism. However, for low nucleation rates, bubble collisions are energetic enough to lead to many well separated vortex-antivortex pairs being produced via the new mechanism. For example, in a simulation involving nucleation of 20 bubbles, a total of 14 non-overlapping vortices and antivortices formed via this new mechanism of pair creation (6 of them being very well separated), as compared to 6 vortices and antivortices produced via the Kibble mechanism. Our results show the possibility that in extremely energetic bubble collisions, such as those in the inflationary models of the early Universe, this new mechanism may drastically affect the defect production scenario.Comment: 8 pages, Revtex, 14 figures. Figs.1a,b and 5a,d are included, rest are availaible on reques