152 research outputs found
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 .
Also, in a rapid heating of a localized region to a temperature {\it below}
, 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
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