42 research outputs found
On the dispersion of fundamental particles in QCD and N=4 Super Yang-Mills theory
We study thermal corrections to the dispersion relations of massive
fundamental particles immersed in weakly coupled non-Abelian plasmas. The cases
covered include quarks in the QCD (quark-gluon) plasma, as well as N=2 quarks
and scalars in an N=4 Super Yang-Mills plasma. We perform the calculations to
leading order in a weak coupling expansion, and consider all mass scales of the
fundamental fields, ranging from massless particles all the way to bare masses
parametrically larger than the temperature.Comment: 41 pages, 8 figures; v2 to be published in JHEP, with one table added
to summarize result
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
Spinning Dragging Strings
We use the AdS/CFT correspondence to compute the drag force experienced by a
heavy quark moving through a maximally supersymmetric SU(N) super Yang-Mills
plasma at nonzero temperature and R-charge chemical potential and at large 't
Hooft coupling. We resolve a discrepancy in the literature between two earlier
studies of such quarks. In addition, we consider small fluctuations of the
spinning strings dual to these probe quarks and find no evidence of
instabilities. We make some comments about suitable D7-brane boundary
conditions for the dual strings.Comment: 25 pages, 4 figures; v2 refs added; v3 to appear in JHEP, clarifying
comment
Debye screening in strongly coupled N=4 supersymmetric Yang-Mills plasma
Using the AdS/CFT correspondence, we examine the behavior of correlators of
Polyakov loops and other operators in N=4 supersymmetric Yang-Mills theory at
non-zero temperature. The implications for Debye screening in this strongly
coupled non-Abelian plasma, and comparisons with available results for thermal
QCD, are discussed.Comment: 21 pages, 5 figures, significantly expanded discussion of Polyakov
loop correlator and static quark-antiquark potentia
Heavy Quark Thermalization in Classical Lattice Gauge Theory: Lessons for Strongly-Coupled QCD
Thermalization of a heavy quark near rest is controlled by the correlator of
two electric fields along a temporal Wilson line. We address this correlator
within real-time, classical lattice Yang-Mills theory, and elaborate on the
analogies that exist with the dynamics of hot QCD. In the weak-coupling limit,
it can be shown analytically that the dynamics on the two sides are closely
related to each other. For intermediate couplings, we carry out
non-perturbative simulations within the classical theory, showing that the
leading term in the weak-coupling expansion significantly underestimates the
heavy quark thermalization rate. Our analytic and numerical results also yield
a general understanding concerning the overall shape of the spectral function
corresponding to the electric field correlator, which may be helpful in
subsequent efforts to reconstruct it from Euclidean lattice Monte Carlo
simulations.Comment: 22 pages. v2: a reference and clarifications added; published versio
Comparing different freeze-out scenarios in azimuthal hadron correlations induced by fast partons
I review the linearized hydrodynamical treatment of a fast parton traversing
a perturbative quark-gluon plasma. Using numerical solutions for the medium's
response to the fast parton, I obtain the medium's distribution function which
is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal
particle spectrum. Two different freeze-out scenarios are considered which
yield significantly different results. I conclude that any meaningful
comparison of azimuthal hadron correlation functions to RHIC data requires
implementing a realistic freeze-out scenario in an expanding medium.Comment: Contribution to the Proceedings for 2008 Hot Quarks in Estes Park,
CO, as accepted for publication in EPJ-
Heavy quark diffusion in QCD and N=4 SYM at next-to-leading order
We present the full details of a calculation at next-to-leading order of the
momentum diffusion coefficient of a heavy quark in a hot, weakly coupled, QCD
plasma. Corrections arise at O(g_s); physically they represent interference
between overlapping scatterings, as well as soft, electric scale (p ~ gT) gauge
field physics, which we treat using the hard thermal loop (HTL) effective
theory. In 3-color, 3-flavor QCD, the momentum diffusion constant of a
fundamental representation heavy quark at NLO is kappa = (16\pi/3) alpha_s^2
T^3 (log(1/g) + 0.07428 + 1.9026 g). We extend the computation to a heavy
fundamental representation ``probe'' quark in large N_c, N=4 Super Yang-Mills
theory, where the result is kappa^{SYM}= (lambda^2 T^3)(6\pi)
(log(1/\sqrt{\lambda}) + 0.4304 + 0.8010 \sqrt{lambda}) (where lambda=g_s^2 N_c
is the t'Hooft coupling). In the absence of some resummation technique, the
convergence of perturbation theory is poor.Comment: 40 pages, 14 figure
Remarks on Heavy-Light Mesons from AdS/CFT
We use the AdS/CFT correspondence to compute the energy spectrum of
heavy-light mesons in a N=2 SU(N) super Yang-Mills theory with two massive
hypermultiplets. In the heavy quark limit, similar to QCD, we find that the
excitation energies are independent of the heavy quark mass. We also make some
remarks about related AdS/CFT models of flavor with less supersymmetry.Comment: 29 pages, 9 figures; v2 section 5 rewritten to include discussion of
long strings, other minor improvements, ref adde
The Energy of a Moving Quark-Antiquark Pair in an N=4 SYM Plasma
We make use of the AdS/CFT correspondence to determine the energy of an
external quark-antiquark pair that moves through strongly-coupled thermal N=4
super-Yang-Mills plasma, both in the rest frame of the plasma and in the rest
frame of the pair. It is found that the pair feels no drag force, has an energy
that reproduces the expected 1/L (or gamma/L) behavior at small quark-antiquark
separations, and becomes unbound beyond a certain screening length whose
velocity-dependence we determine. We discuss the relation between the
high-velocity limit of our results and the lightlike Wilson loop proposed
recently as a definition of the jet-quenching parameter.Comment: LaTeX 2e, 27 pages, 8 eps figures; v2: added computation of the pair
energy in the plasma rest frame, clarified the comparison with
hep-ph/0607062, corrected typos, added reference
The dynamics of quark-gluon plasma and AdS/CFT
In these pedagogical lectures, we present the techniques of the AdS/CFT
correspondence which can be applied to the study of real time dynamics of a
strongly coupled plasma system. These methods are based on solving
gravitational Einstein's equations on the string/gravity side of the AdS/CFT
correspondence. We illustrate these techniques with applications to the
boost-invariant expansion of a plasma system. We emphasize the common
underlying AdS/CFT description both in the large proper time regime where
hydrodynamic dynamics dominates, and in the small proper time regime where the
dynamics is far from equilibrium. These AdS/CFT methods provide a fascinating
arena interrelating General Relativity phenomenae with strongly coupled gauge
theory physics.Comment: 35 pages, 3 figures. Lectures at the 5th Aegean summer school, `From
gravity to thermal gauge theories: the AdS/CFT correspondence'. To appear in
the proceedings in `Lecture Notes in Physics