608 research outputs found
Heavy flavor diffusion in weakly coupled N=4 Super Yang-Mills theory
We use perturbation theory to compute the diffusion coefficient of a heavy
quark or scalar moving in N=4 SU(N_c) Super Yang-Mills plasma to leading order
in the coupling and the ratio T/M<<1. The result is compared both to recent
strong coupling calculations in the same theory and to the corresponding weak
coupling result in QCD. Finally, we present a compact and simple formulation of
the Lagrangian of our theory, N=4 SYM coupled to a massive fundamental N=2
hypermultiplet, which is well-suited for weak coupling expansions.Comment: 22 pages, 4 figures; v3: error corrected in calculations, figures and
discussion modified accordingl
Hard thermal loops and the entropy of supersymmetric Yang-Mills theories
We apply the previously proposed scheme of approximately self-consistent
hard-thermal-loop resummations in the entropy of high-temperature QCD to N=4
supersymmetric Yang-Mills (SYM) theories and compare with a (uniquely
determined) R[4,4] Pad\'e approximant that interpolates accurately between the
known perturbative result and the next-to-leading order strong-coupling result
obtained from AdS/CFT correspondence. We find good agreement up to couplings
where the entropy has dropped to about 85% of the Stefan-Boltzmann value. This
is precisely the regime which in purely gluonic QCD corresponds to temperatures
above 2.5 times the deconfinement temperature and for which this method of
hard-thermal-loop resummation has given similar good agreement with lattice QCD
results. This suggests that in this regime the entropy of both QCD and N=4 SYM
is dominated by effectively weakly coupled hard-thermal-loop quasiparticle
degrees of freedom. In N=4 SYM, strong-coupling contributions to the
thermodynamic potential take over when the entropy drops below 85% of the
Stefan-Boltzmann value.Comment: 14 pages, 2 figures, JHEP3. v2: revised and expanded, with unchanged
HTL results but corrected NLO strong-coupling result from AdS/CFT (which is
incorrectly reproduced in almost all previous papers comparing weak and
strong coupling results of N=4 SYM) and novel (unique) Pade approximant
interpolating between weak and strong coupling result
Dissipative force on an external quark in heavy quark cloud
Within the finite temperature N = 4 strongly coupled super Yang- Mills, we
compute the dissipative force on an external quark in the presence of evenly
distributed heavy quark cloud. This is computed holographically by constructing
the corresponding gravity dual. We study the behaviour of this force as a
function of the cloud density. Along the way we also analyze the stability of
the gravity dual for vector and tensor perturbations.Comment: 14 pages, 2 figures, significant improvements, to be appeared in
Physics Letters
The Hydrodynamics of M-Theory
We consider the low energy limit of a stack of N M-branes at finite
temperature. In this limit, the M-branes are well described, via the AdS/CFT
correspondence, in terms of classical solutions to the eleven dimensional
supergravity equations of motion. We calculate Minkowski space two-point
functions on these M-branes in the long-distance, low-frequency limit, i.e. the
hydrodynamic limit, using the prescription of Son and Starinets
[hep-th/0205051]. From these Green's functions for the R-currents and for
components of the stress-energy tensor, we extract two kinds of diffusion
constant and a viscosity. The N dependence of these physical quantities may
help lead to a better understanding of M-branes.Comment: 1+19 pages, references added, section 5 clarified, eq. (72) correcte
Jet quenching within a hybrid strong/weak coupling approach
We propose a novel hybrid model for jet quenching, including both strong and
weak coupling physics where each seems appropriate. Branching in the parton
shower is assumed to be perturbative and described by DGLAP evolution, while
interactions with the medium result in each parton in the shower losing energy
as at strong coupling, as realized holographically. The medium-modified parton
shower is embedded into a hydrodynamic evolution of hot QCD plasma and
confronted with LHC jet data.Comment: 5 pages, 6 figures, Quark Matter 2014 proceeding
String Theory and Quantum Chromodynamics
I review recent progress on the connection between string theory and quantum
chromodynamics in the context of the gauge/gravity duality. Emphasis is placed
on conciseness and conceptual aspects rather than on technical details. Topics
covered include the large-Nc limit of gauge theories, the gravitational
description of gauge theory thermodynamics and hydrodynamics, and
confinement/deconfinement thermal phase transitions.Comment: 38 pages, 24 figures. Lectures given at the RTN Winter School on
"Strings, Supergravity and Gauge Theories" at CERN on January 15-19, 200
Shear Viscosity to Entropy Density Ratio of QCD below the Deconfinement Temperature
Using chiral perturbation theory we investigate the QCD shear viscosity to
entropy density ratio below the deconfinement temperature (~170 MeV) with zero
baryon number density. It is found that the viscosity to entropy density ratio
of QCD is monotonically decreasing in temperature (T) and reaches 0.6 with
estimated ~50% uncertainty at T=120 MeV. A naive extrapolation of the leading
order result shows that the ratio reaches the 1/(4 pi) minimum bound proposed
by Kovtun, Son, and Starinets using string theory methods at T~200 MeV. This
suggests a phase transition or cross over might occur at T less than 200 MeV in
order for the bound to remain valid. Also, it is natural for the ratio to stay
close to the minimum bound around the phase transition temperature as was
recently found in heavy ion collisions.Comment: 12 pages and 2 figure
Parton Energy Loss in Strongly Coupled AdS/CFT
This is a brief review of the theory and phenomenology of parton energy loss
in strongly coupled field theories with a gravity dual and its comparison with
parton energy loss in QCD at weak coupling.Comment: Invited lecture at Hard Probes 2010, Eilat, Israel. Error in Table 1
and Fig. 7 corrected (thanks to E. Iancu
Transition from ergodic to explosive behavior in a family of stochastic differential equations
We study a family of quadratic stochastic differential equations in the
plane, motivated by applications to turbulent transport of heavy particles.
Using Lyapunov functions, we find a critical parameter value
such that when the system is
ergodic and when solutions are not defined for all
times. H\"{o}rmander's hypoellipticity theorem and geometric control theory are
also utilized.Comment: 35 pages, 6 figure
Bulk viscosity of gauge theory plasma at strong coupling
We propose a lower bound on bulk viscosity of strongly coupled gauge theory
plasmas. Using explicit example of the N=2^* gauge theory plasma we show that
the bulk viscosity remains finite at a critical point with a divergent specific
heat. We present an estimate for the bulk viscosity of QGP plasma at RHIC.Comment: 5 pages, 4 figure
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