3,201 research outputs found
Two-dimensional gauge theories of the symmetric group S(n) and branched n-coverings of Riemann surfaces in the large-n limit
Branched n-coverings of Riemann surfaces are described by a 2d lattice gauge
theory of the symmetric group S(n) defined on a cell discretization of the
surface. We study the theory in the large-n limit, and we find a rich phase
diagram with first and second order transition lines. The various phases are
characterized by different connectivity properties of the covering surface. We
point out some interesting connections with the theory of random walks on group
manifolds and with random graph theory.Comment: Talk presented at the "Light-cone physics: particles and strings",
Trento, Italy, September 200
Poincar\'e Gauge Theories for Lineal Garvity
We have shown that two of the most studied models of lineal gravities -
Liouville gravity and a ``string-inspired'' model exhibiting the main
characteristic features of a black-hole solution - can be formulated as gauge
invariant theories of the Poincar\'e group. The gauge invariant couplings to
matter (particles, scalar and spinor fields) and explicit solutions for some
matter field configurations, are provided. It is shown that both the models, as
well as the couplings to matter, can be obtained as suitable dimensional
reductions of a 2+1-dimensional ISO(2,1) gauge invariant theory.Comment: TeX Manuscript, 30 page
On the chiral and deconfinement phase transitions in parity-conserving QED_3 at finite temperature
We present some results about the interplay between the chiral and
deconfinement phase transitions in parity-conserving QED3 (with N flavours of
massless 4 component fermions) at finite temperature. Following Grignani et al
(Phys. Rev. D53, 7157 (1996), Nucl. Phys. B473, 143 (1996)), confinement is
discussed in terms of an effective Sine-Gordon theory for the timelike
component of the gauge field A_0. But whereas in the references above the
fermion mass m is a Lagrangian parameter, we consider the m=0 case and ask
whether an effective S-G theory can again be derived with m replaced by the
dynamically generated mass Sigma which appears below T_{ch}, the critical
temperature for the chiral phase transition. The fermion and gauge sectors are
strongly interdependent, but as a first approximation we decouple them by
taking Sigma to be a constant, depending only on the constant part of the gauge
field. We argue that the existence of a low-temperature confining phase may be
associated with the generation of Sigma; and that, analogously, the vanishing
of Sigma for T > T_{ch} drives the system to its deconfining phase. The effect
of the gauge field dynamics on mass generation is also indicated. (38kb)Comment: 1 reference adde
Thermal DBI action for the D3-brane at weak and strong coupling
We study the effective action for finite-temperature D3-branes with an
electromagnetic field at weak and strong coupling. We call this action the
thermal DBI action. Comparing at low temperature the leading correction
for the thermal DBI action at weak and strong coupling we find that the
factor well-known from the AdS/CFT correspondence extends to the case of
arbitrary electric and magnetic fields on the D3-brane. We investigate the
reason for this by taking the decoupling limit in both the open and the closed
string descriptions thus showing that the AdS/CFT correspondence extends to the
case of arbitrary constant electric and magnetic fields on the D3-brane.Comment: 30 pages, no figure
Loop Correlators and Theta States in 2D Yang-Mills Theory
Explicit computations of the partition function and correlation functions of
Wilson and Polyakov loop operators in theta-sectors of two dimensional
Yang-Mills theory on the line cylinder and torus are presented. Several
observations about the correspondence of two dimensional Yang-Mills theory with
unitary matrix quantum mechanics are presented. The incorporation of the
theta-angle which characterizes the states of two dimensional adjoint QCD is
discussed.Comment: 30 pages, Latex, no figure
Charge Screening in the Finite Temperature Schwinger Model
We compute the effective action and correlators of the Polyakov loop operator
in the Schwinger model at finite temperature and discuss the realization of the
discrete symmetries that occur there. We show that, due to nonlocal effects of
massless fermions in two spacetime dimensions, the discrete symmetry which
governs the screening of charges is spontaneously broken even in an effective
one-dimensional model, when the volume is infinite. In this limit, the thermal
state of the Schwinger model screens an arbitrary external charge; consequently
the model is in the deconfined phase, with the charge of the deconfined
fermions completely screened. In a finite volume we show that the Schwinger
model is always confining.Comment: 27 pages, latex, no figures. References addded and some misprints
correcte
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