6 research outputs found
Holographic dual of collimated radiation
We propose a new and simple method of estimating the radiation due to an
accelerated quark in a strongly coupled medium, within the framework of the
AdS/CFT correspondence. In particular, we offer a heuristic explanation of the
collimated nature of synchrotron radiation produced by a circling quark, which
was recently studied in Phys.Rev.D81 (2010) 126001. The gravitational dual of
such quark is a coiling string in AdS, whose backreaction on the spacetime
geometry remains tightly confined, as if 'beamed' towards the boundary. While
this appears to contradict conventional expectations from the scale/radius
duality, we resolve the issue by observing that the backreaction of a
relativistic string is reproduced by a superposition of gravitational shock
waves. We further demonstrate that this proposal allows us to reduce the
problem of computing the boundary stress tensor to merely calculating geodesics
in AdS, as opposed to solving linearized Einstein's equations.Comment: 26 pages, 6 figures, invited contribution to the New Journal of
Physics Focus Issue "Strongly Correlated Quantum Fluids: From Ultracold
Quantum Gases to QCD Plasmas
Conical Emission in Heavy Ion Collisions
A broadened or double humped away-side structure was observed in 2-particle
azimuthal jet-like correlations at RHIC and SPS. This modification can be
explained by conical emission, from either Mach-cone shock waves or Cherenkov
gluon radiation, and by other physics mechanisms, such as large angle gluon
radiation, jets deflected by radial flow and path-length dependent energy loss.
Three-particle jet-like correlations are studied for their power to distinguish
conical emission from other mechanisms. This article discusses Mach-cone shock
waves, Cherenkov gluon radiation and the experimental evidence for conical
emission from RHIC and SPS.Comment: Talk given at QM2008, Jaipur, India. 8 pages, 7 figure
Dressed spectral densities for heavy quark diffusion in holographic plasmas
We analyze the large frequency behavior of the spectral densities that govern
the generalized Langevin diffusion process for a heavy quark in the context of
the gauge/gravity duality. The bare Langevin correlators obtained from the
trailing string solution have a singular short-distance behavior. We argue that
the proper dressed spectral functions are obtained by subtracting the
zero-temperature correlators. The dressed spectral functions have a
sufficiently fast fall-off at large frequency so that the Langevin process is
well defined and the dispersion relations are satisfied. We identify the cases
in which the subtraction does not modify the associated low-frequency transport
coefficients. These include conformal theories and the non-conformal,
non-confining models. We provide several analytic and numerical examples in
conformal and non-conformal holographic backgrounds.Comment: 51 pages, 2 figure
Holographic Lessons for Quark Dynamics
We give a brief overview of recent results obtained through the gauge/gravity
correspondence, concerning the propagation of a heavy quark in strongly-coupled
conformal field theories (such as N=4 super-Yang-Mills), both at zero and
finite temperature. In the vacuum, we discuss energy loss, radiation damping,
signal propagation and radiation-induced fluctuations. In the presence of a
thermal plasma, our emphasis is on early-time energy loss, screening and
quark-antiquark evolution after pair creation. Throughout, quark dynamics is
seen to be efficiently encapsulated in the usual string worldsheet dynamics.Comment: Invited review for a Journal of Physics G topical volume on
gauge/gravity duality applications to QCD matter and ultrarelativistic
heavy-ion collisions. v2: Reference adde