2,308 research outputs found
Drag force in a string model dual to large-N QCD
We compute the drag force exerted on a quark and a di-quark systems in a
background dual to large-N QCD at finite temperature. We find that appears a
drag force in the former setup with flow of energy proportional to the mass of
the quark while in the latter there is no dragging as in other studies. We also
review the screening length.Comment: 15 pages, typos removed, error corrected, refs adde
New Supergravity Backgrounds Dual to N=1 SQCD-like Theories with N_f=2N_c
We present new supergravity backgrounds generated by N_c D5-branes, wrapping
the S^2 of the resolved conifold, in the presence of N_f = 2 N_c smeared flavor
D5-branes. The smearing allows us to take their backreaction on the geometry
into account. We discuss the consistency, stability, and supersymmetry of these
types of setups. We find near horizon geometries that we expect to be
supergravity duals of SQCD-like theories with N_f= 2N_c. From these backgrounds
we numerically extract rectangular Wilson loops and beta functions of the dual
field theory for the regime where our approximations are valid.Comment: 22+24 pages, 17 figures, Figure 12 replace
The intrinsic three-dimensional shape of galactic bars
We present the first statistical study on the intrinsic three-dimensional
(3D) shape of a sample of 83 galactic bars extracted from the CALIFA survey. We
use the galaXYZ code to derive the bar intrinsic shape with a statistical
approach. The method uses only the geometric information (ellipticities and
position angles) of bars and discs obtained from a multi-component photometric
decomposition of the galaxy surface-brightness distributions. We find that bars
are predominantly prolate-triaxial ellipsoids (68%), with a small fraction of
oblate-triaxial ellipsoids (32%). The typical flattening (intrinsic C/A
semiaxis ratio) of the bars in our sample is 0.34, which matches well the
typical intrinsic flattening of stellar discs at these galaxy masses. We
demonstrate that, for prolate-triaxial bars, the intrinsic shape of bars
depends on the galaxy Hubble type and stellar mass (bars in massive S0 galaxies
are thicker and more circular than those in less massive spirals). The bar
intrinsic shape correlates with bulge, disc, and bar parameters. In particular
with the bulge-to-total (B/T) luminosity ratio, disc g-r color, and central
surface brightness of the bar, confirming the tight link between bars and their
host galaxies. Combining the probability distributions of the intrinsic shape
of bulges and bars in our sample we show that 52% (16%) of bulges are thicker
(flatter) than the surrounding bar at 1 level. We suggest that these
percentages might be representative of the fraction of classical and disc-like
bulges in our sample, respectively.Comment: 18 pages, 11 figures, accepted for publication in MNRA
No-Drag String Configurations for Steadily Moving Quark-Antiquark Pairs in a Thermal Bath
We investigate the behavior of stationary string configurations on a
five-dimensional AdS black hole background which correspond to quark-antiquark
pairs steadily moving in an N=4 super Yang-Mills thermal bath. There are many
branches of solutions, depending on the quark velocity and separation as well
as on whether Euclidean or Lorentzian configurations are examined.Comment: references added; statements corrected; eliminated computation of jet
quenching parameter from Wilson loop of [Liu, Rajagopal, Wiedemann,
hep-th/0605178] using Euclidean string configurations since those authors
advocate [hep-th/0607062, footnote 14] the use of spacelike Lorentzian string
configurations instea
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
Screening length and the direction of plasma winds
We study the screening length of a heavy quark-antiquark pair in strongly
coupled gauge theory plasmas flowing at velocity v following a proposal by Liu,
Rajagopal, and Wiedemann. We analyze the screening length as the direction of
the plasma winds vary. To leading order in v, this angle-dependence can be
studied analytically for many theories by extending our previous formalism. We
show that the screening length is locally a minimum (maximum) when the pair is
perpendicular (parallel) to the plasma winds, which has been observed for the
N=4 plasma. Also, we compare AdS/CFT results with weak coupling ones, and we
discuss the subleading dependence on v for the Dp-brane.Comment: 20 pages, 4 figures, JHEP3; v2: discussion added and modifie
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