6 research outputs found
Strongly coupled matter near phase transition
In the Hartree approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism of
the real scalar field theory, we show that for the strongly coupled scalar
system near phase transition, the shear viscosity over entropy density is
small, however, the bulk viscosity over entropy density is large. The large
bulk viscosity is related to the highly nonconformal equation of state. It is
found that the square of the sound velocity near phase transition is much
smaller than the conformal value 1/3, and the trace anomaly at phase transition
deviates far away from 0. These results agree well with the lattice results of
the complex QCD system near phase transition.Comment: 6 pages, 2 figures, 1 table, contributed to the International
Conference on Strangeness in Quark Matter 2008, Beijing, China, 6-10 October
200
Parton picture for the strongly coupled SYM plasma
Deep inelastic scattering off the strongly coupled N=4 supersymmetric
Yang-Mills plasma at finite temperature can be computed within the AdS/CFT
correspondence, with results which are suggestive of a parton picture for the
plasma. Via successive branchings, essentially all partons cascade down to very
small values of the longitudinal momentum fraction x and to transverse momenta
smaller than the saturation momentum Q_s\sim T/x. This scale Q_s controls the
plasma interactions with a hard probe, in particular, the jet energy loss and
its transverse momentum broadening.Comment: 4 pages, Talk given at Quark Matter 2008: 20th International
Conference on Ultra-Relativistic Nucleus Nucleus Collisions (QM 2008),
Jaipur, India, 4-10 Feb 200
Quantum criticality and black holes
Many condensed matter experiments explore the finite temperature dynamics of
systems near quantum critical points. Often, there are no well-defined
quasiparticle excitations, and so quantum kinetic equations do not describe the
transport properties completely. The theory shows that the transport
co-efficients are not proportional to a mean free scattering time (as is the
case in the Boltzmann theory of quasiparticles), but are completely determined
by the absolute temperature and by equilibrium thermodynamic observables.
Recently, explicit solutions of this quantum critical dynamics have become
possible via the AdS/CFT duality discovered in string theory. This shows that
the quantum critical theory provides a holographic description of the quantum
theory of black holes in a negatively curved anti-de Sitter space, and relates
its transport co-efficients to properties of the Hawking radiation from the
black hole. We review how insights from this connection have led to new results
for experimental systems: (i) the vicinity of the superfluid-insulator
transition in the presence of an applied magnetic field, and its possible
application to measurements of the Nernst effect in the cuprates, (ii) the
magnetohydrodynamics of the plasma of Dirac electrons in graphene and the
prediction of a hydrodynamic cyclotron resonance.Comment: 12 pages, 2 figures; Talk at LT25, Amsterda
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