1,248 research outputs found
Volume independence in large Nc QCD-like gauge theories
Volume independence in large \Nc gauge theories may be viewed as a
generalized orbifold equivalence. The reduction to zero volume (or Eguchi-Kawai
reduction) is a special case of this equivalence. So is temperature
independence in confining phases. In pure Yang-Mills theory, the failure of
volume independence for sufficiently small volumes (at weak coupling) due to
spontaneous breaking of center symmetry, together with its validity above a
critical size, nicely illustrate the symmetry realization conditions which are
both necessary and sufficient for large \Nc orbifold equivalence. The
existence of a minimal size below which volume independence fails also applies
to Yang-Mills theory with antisymmetric representation fermions [QCD(AS)].
However, in Yang-Mills theory with adjoint representation fermions [QCD(Adj)],
endowed with periodic boundary conditions, volume independence remains valid
down to arbitrarily small size. In sufficiently large volumes, QCD(Adj) and
QCD(AS) have a large \Nc ``orientifold'' equivalence, provided charge
conjugation symmetry is unbroken in the latter theory. Therefore, via a
combined orbifold-orientifold mapping, a well-defined large \Nc equivalence
exists between QCD(AS) in large, or infinite, volume and QCD(Adj) in
arbitrarily small volume. Since asymptotically free gauge theories, such as
QCD(Adj), are much easier to study (analytically or numerically) in small
volume, this equivalence should allow greater understanding of large \Nc QCD
in infinite volume.Comment: 32 pages, 4 figure
Necessary and sufficient conditions for non-perturbative equivalences of large N orbifold gauge theories
Large N coherent state methods are used to study the relation between U(N)
gauge theories containing adjoint representation matter fields and their
orbifold projections. The classical dynamical systems which reproduce the large
N limits of the quantum dynamics in parent and daughter orbifold theories are
compared. We demonstrate that the large N dynamics of the parent theory,
restricted to the subspace invariant under the orbifold projection symmetry,
and the large N dynamics of the daughter theory, restricted to the untwisted
sector invariant under "theory space'' permutations, coincide. This implies
equality, in the large N limit, between appropriately identified connected
correlation functions in parent and daughter theories, provided the orbifold
projection symmetry is not spontaneously broken in the parent theory and the
theory space permutation symmetry is not spontaneously broken in the daughter.
The necessity of these symmetry realization conditions for the validity of the
large N equivalence is unsurprising, but demonstrating the sufficiency of these
conditions is new. This work extends an earlier proof of non-perturbative large
N equivalence which was only valid in the phase of the (lattice regularized)
theories continuously connected to large mass and strong coupling.Comment: 21 page, JHEP styl
Universal properties of thermal and electrical conductivity of gauge theory plasmas from holography
We propose that for conformal field theories admitting gravity duals, the
thermal conductivity is fixed by the central charges in a universal manner.
Though we do not have a proof as yet, we have checked our proposal against
several examples. This proposal, if correct, allows us to express electrical
conductivity in terms of thermodynamical quantities even in the presence of
chemical potential.Comment: 13 pages, appendix added, close to journal versio
Holographic Confining Gauge theory and Response to Electric Field
We study the response of confining gauge theory to the external electric
field by using holographic Yang-Mills theories in the large limit.
Although the theories are in the confinement phase, we find a transition from
the insulator to the conductor phase when the electric field exceeds its
critical value. Then, the baryon number current is generated in the conductor
phase. At the same time, in this phase, the meson melting is observed through
the quasi-normal modes of meson spectrum. Possible ideas are given for the
string state corresponding to the melted mesons, and they lead to the idea that
the source of this current may be identified with the quarks and anti-quarks
supplied by the melted mesons. We also discuss about other possible carriers.
Furthermore, from the analysis of the massless quark, chiral symmetry
restoration is observed at the insulator-conductor transition point by studying
a confining theory in which the chiral symmetry is broken.Comment: 27 pages, 14 figure
Small volume expansion of almost supersymmetric large N theories
We consider the small-volume dynamics of nonsupersymmetric orbifold and
orientifold field theories defined on a three-torus, in a test of the claimed
planar equivalence between these models and appropriate supersymmetric ``parent
models". We study one-loop effective potentials over the moduli space of flat
connections and find that planar equivalence is preserved for suitable averages
over the moduli space. On the other hand, strong nonlinear effects produce
local violations of planar equivalence at special points of moduli space. In
the case of orbifold models, these effects show that the "twisted" sector
dominates the low-energy dynamics.Comment: 20 pages, 3 figures; added references, minor change
A transport coefficient: the electrical conductivity
I describe the lattice determination of the electrical conductivity of the
quark gluon plasma. Since this is the first extraction of a transport
coefficient with a degree of control over errors, I next use this to make
estimates of other transport related quantities using simple kinetic theory
formulae. The resulting estimates are applied to fluctuations, ultra-soft
photon spectra and the viscosity. Dimming of ultra-soft photons is exponential
in the mean free path, and hence is a very sensitive probe of transport.Comment: Talk given in ICPAQGP 2005, SINP, Kolkat
Constraints on Superfluid Hydrodynamics from Equilibrium Partition Functions
Following up on recent work in the context of ordinary fluids, we study the
equilibrium partition function of a 3+1 dimensional superfluid on an arbitrary
stationary background spacetime, and with arbitrary stationary background gauge
fields, in the long wavelength expansion. We argue that this partition function
is generated by a 3 dimensional Euclidean effective action for the massless
Goldstone field. We parameterize the general form of this action at first order
in the derivative expansion. We demonstrate that the constitutive relations of
relativistic superfluid hydrodynamics are significantly constrained by the
requirement of consistency with such an effective action. At first order in the
derivative expansion we demonstrate that the resultant constraints on
constitutive relations coincide precisely with the equalities between
hydrodynamical transport coefficients recently derived from the second law of
thermodynamics.Comment: 46 page
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