813 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
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
First search for double-beta decay of 184Os and 192Os
A search for double-beta decay of osmium has been realized for the first time
with the help of an ultra-low background HPGe gamma detector at the underground
Gran Sasso National Laboratories of the INFN (Italy). After 2741 h of data
taking with a 173 g ultra-pure osmium sample limits on double-beta processes in
184Os have been established at the level of T_{1/2} about 10^{14}-10^{17} yr.
Possible resonant double-electron captures in 184Os were searched for with a
sensitivity T_{1/2} about 10^{16} yr. A half-life limit T_{1/2} > 5.3 10^{19}
yr was set for the double-beta decay of 192Os to the first excited level of
192Pt. The radiopurity of the osmium sample has been investigated and
radionuclides 137Cs, 185Os and 207Bi were detected in the sample, while
activities of 40K, 60Co, 226Ra and 232Th were limited at the mBq/kg level.Comment: 12 pages, 7 figures, 2 table
Search for 2\beta\ decays of 96Ru and 104Ru by ultra-low background HPGe gamma spectrometry at LNGS: final results
An experiment to search for double beta decay processes in 96Ru and 104Ru,
which are accompanied by gamma rays, has been realized in the underground Gran
Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with
masses of about (0.5-0.7) kg were measured with the help of ultra-low
background high purity Ge gamma ray spectrometry. After 2162 h of data taking
the samples were deeply purified to reduce the internal contamination of 40K.
The last part of the data has been accumulated over 5479 h. New improved half
life limits on 2\beta+/\epsilon \beta+/2\epsilon\ processes in 96Ru have been
established on the level of 10^{20} yr, in particular for decays to the ground
state of 96Mo: T1/2(2\nu 2\beta+) > 1.4 10^{20} yr, T1/2(2\nu \epsilon\beta+) >
8.0 10^{19} yr and T1/2(0\nu 2K) > 1.0 10^{21} yr (all limits are at 90% C.L.).
The resonant neutrinoless double electron captures to the 2700.2 keV and 2712.7
keV excited states of 96Mo are restricted as: T1/2(0\nu KL) > 2.0 10^{20} yr
and T1/2(0\nu 2L) > 3.6 10^{20} yr, respectively. Various two neutrino and
neutrinoless 2\beta\ half lives of 96Ru have been estimated in the framework of
the QRPA approach. In addition, the T1/2 limit for 0\nu 2\beta- transitions of
104Ru to the first excited state of 104Pd has been set as > 6.5 10^{20} yr.Comment: 14 pages, 5 figures, 2 tables; version accepted for publication on
Phys. Rev.
Center symmetry and the orientifold planar equivalence
We study the center symmetry of SU(N) gauge theories with fermions in the
two-index representations, by computing the effective potential of the Polyakov
loop in the large-mass expansion on the lattice. In the large-N limit and at
non-zero temperature, we find that the center symmetry is Z_N for fermions in
the adjoint representation and just Z_2 for fermions in the (anti)symmetric
representation. We discuss the fact that our results do not contradict the
orientifold planar equivalence, which relates a common sector defined by the
bosonic gauge-invariant C-even states of theories with fermions in different
two-index representations. Our results complement the work of Armoni et al.
(2007), who showed how at zero temperature a Z_N center symmetry is dynamically
recovered also for fermions in the (anti)symmetric representation, by
considering the theories at finite temperature.Comment: 27 pages, 7 eps figure
Large N reduction on group manifolds
We show that the large N reduction holds on group manifolds. Large N field
theories defined on group manifolds are equivalent to some corresponding matrix
models. For instance, gauge theories on S^3 can be regularized in a gauge
invariant and SO(4) invariant manner.Comment: 21 pages, 4 figures, typos corrected, a reference adde
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