723 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
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
The ultraviolet limit and sum rule for the shear correlator in hot Yang-Mills theory
We determine a next-to-leading order result for the correlator of the shear
stress operator in high-temperature Yang-Mills theory. The computation is
performed via an ultraviolet expansion, valid in the limit of small distances
or large momenta, and the result is used for writing operator product
expansions for the Euclidean momentum and coordinate space correlators as well
as for the Minkowskian spectral density. In addition, our results enable us to
confirm and refine a shear sum rule originally derived by Romatschke, Son and
Meyer.Comment: 16 pages, 2 figures. v2: small clarifications, one reference added,
published versio
A note on conductivity and charge diffusion in holographic flavour systems
We analyze the charge diffusion and conductivity in a Dp/Dq holographic setup
that is dual to a supersymmetric Yang-Mills theory in p+1 dimensions with N_f<<
N_c flavour degrees of freedom at finite temperature and nonvanishing U(1)
baryon number chemical potential. We provide a new derivation of the results
that generalize the membrane paradigm to the present context. We perform a
numerical analysis in the particular case of the D3/D7 flavor system. The
results obtained support the validity of the Einstein relation at finite
chemical potential.Comment: 15 pages, 3 figures, v2 with minor correction
Застосування технологій E-learning в курсі англійської мови для аспірантів у НТУ "ХПІ"
The experience of introduction of E-learning into the English course for post-graduates at NTU "KhPI" is discussed. The major advantages of blended education in studying a foreign language are analyzed. It is concluded that introduction of distance education may be very effective especially for adult learners.Розглядається досвід впровадження технологій E-learning в курс англійської мови для аспірантів в НТУ «ХПІ». Аналізуються основні переваги «змішаного» навчання при вивченні іноземної мови. Робиться висновок, що застосування дистанційної освіти може буди достатньо ефективним, особливо для дорослих студенті
The centrality dependence of v2/epsilon: the ideal hydro limit and eta/s
The large elliptic flow observed at RHIC is considered to be evidence for
almost perfect liquid behavior of the strongly coupled quark-gluon plasma
produced in the collisions. In these proceedings we present a two parameter fit
for the centrality dependence of the elliptic flow scaled by the spatial
eccentricity. We show by comparing to viscous hydrodynamical calculations that
these two parameters are in good approximation proportional to the shear
viscosity over entropy ratio and the ideal hydro limit of the ratio v2/epsilon.Comment: 4 pages, 8 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee - final version
without line number
Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant
We compute the dimensionality dependence of for charged black branes
with Gauss-Bonnet correction. We find that both causality and stability
constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in
the infinite dimensionality limit. We further show that higher dimensionality
stabilize the gravitational perturbation. The stabilization of the perturbation
in higher dimensional space-time is a straightforward consequence of the
Gauss-Bonnet coupling constant bound.Comment: 16 pages,3 figures+3 tables,typos corrected, published versio
On Classical Equivalence Between Noncritical and Einstein Gravity : The AdS/CFT Perspectives
We find that noncritical gravity, a special class of higher derivative
gravity, is classically equivalent to Einstein gravity at the full nonlinear
level. We obtain the viscosity-to-entropy ratio and the second order transport
coefficients of the dual fluid of noncritical gravity to all orders in the
coupling of higher derivative terms. We also compute the holographic
entanglement entropy in the dual CFT of noncritical gravity. All these results
confirm the nonlinear equivalence between noncritical gravity and Einstein
gravity at the classical level.Comment: 19 pages, no figure
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