32 research outputs found
Fermion correlators in non-abelian holographic superconductors
We consider fermion correlators in non-abelian holographic superconductors.
The spectral function of the fermions exhibits several interesting features
such as support in displaced Dirac cones and an asymmetric distribution of
normal modes. These features are compared to similar ones observed in angle
resolved photoemission experiments on high T_c superconductors. Along the way
we elucidate some properties of p-wave superconductors in AdS_4 and discuss the
construction of SO(4) superconductors.Comment: 49 pages, 11 figure
Pointlike probes of superstring-theoretic superfluids
In analogy with an experimental setup used in liquid helium, we use a
pointlike probe to study superfluids which have a gravity dual. In the gravity
description, the probe is represented by a hanging string. We demonstrate that
there is a critical velocity below which the probe particle feels neither drag
nor stochastic forces. Above this critical velocity, there is power-law scaling
for the drag force, and the stochastic forces are characterized by a finite,
velocity-dependent temperature. This temperature participates in two simple and
general relations between the drag force and stochastic forces. The formula we
derive for the critical velocity indicates that the low-energy excitations are
massless, and they demonstrate the power of stringy methods in describing
strongly coupled superfluids.Comment: 17 pages, 2 figures, added a figure, a reference, and moved material
to an appendi
Gauge gravity duality for d-wave superconductors: prospects and challenges
We write down an action for a charged, massive spin two field in a fixed
Einstein background. Despite some technical problems, we argue that in an
effective field theory framework and in the context of the AdS/CFT
correspondence, this action can be used to study the properties of a superfluid
phase transition with a d-wave order parameter in a dual strongly interacting
field theory. We investigate the phase diagram and the charge conductivity of
the superfluid phase. We also explain how possible couplings between the spin
two field and bulk fermions affect the fermion spectral function.Comment: 42 pages, 6 figure
Scanning the Parameter Space of Holographic Superconductors
We study various physical quantities associated with holographic s-wave
superconductors as functions of the scaling dimensions of the dual condensates.
A bulk scalar field with negative mass squared , satisfying the
Breitenlohner-Freedman stability bound and the unitarity bound, and allowed to
vary in unit intervals, were considered. We observe that all the physical
quantities investigated are sensitive to the scaling dimensions of the dual
condensates. For all the , the characteristic lengths diverge at the
critical temperature in agreement with the Ginzburg-Landau theory. The
Ginzburg-Landau parameter, obtained from these length scales indicates that the
holographic superconductors can be type I or type II depending on the charge
and the scaling dimensions of the dual condensates. For a fixed charge, there
exists a critical scaling dimension, above which a holographic superconductor
is type I, below which it becomes a type II.Comment: 24 pages 47 figure
On the Beaming of Gluonic Fields at Strong Coupling
We examine the conditions for beaming of the gluonic field sourced by a heavy
quark in strongly-coupled conformal field theories, using the AdS/CFT
correspondence. Previous works have found that, contrary to naive expectations,
it is possible to set up collimated beams of gluonic radiation despite the
strong coupling. We show that, on the gravity side of the correspondence, this
follows directly (for arbitrary quark motion, and independently of any
approximations) from the fact that the string dual to the quark remains
unexpectedly close to the AdS boundary whenever the quark moves
ultra-relativistically. We also work out the validity conditions for a related
approximation scheme that proposed to explain the beaming effect though the
formation of shock waves in the bulk fields emitted by the string. We find that
these conditions are fulfilled in the case of ultra-relativistic uniform
circular motion that motivated the proposal, but unfortunately do not hold for
much more general quark trajectories.Comment: 1+33 pages, 2 figure
Absence of a Fermi surface in classical minimal four-dimensional gauged supergravity
We demonstrate that the two point function of the supercurrent dual to the
gravitino in the four-dimensional extremal anti-de Sitter Reissner-Nordstrom
black hole does not exhibit a Fermi surface singularity. In our analysis, we
utilize the ingoing Eddington-Finkelstein coordinate system, which enables us
to bypass certain complications in the determination of the allowed near
horizon behavior of the gravitino field at zero frequency. We check that our
method agrees with previous results for the massless charged Dirac field.Comment: 12 pages, 1 figur
Quark-Gluon Plasma - New Frontiers
As implied by organizers, this talk is not a conference summary but rather an
outline of progress/challenges/``frontiers'' of the theory. Some fundamental
questions addressed are:
Why is sQGP such a good liquid? Do we understand (de)confinement and what do
we know about ``magnetic'' objects creating it? Can we understand the AdS/CFT
predictions, from the gauge theory side? Can they be tested experimentally? Can
AdS/CFT duality help us understand rapid equilibration/entropy production? Can
we work out a complete dynamical ``gravity dual'' to heavy ion collisions?Comment: final talk at Quark Matter 2008, Jaipur, India, Feb.200
Drag force in a strongly coupled anisotropic plasma
We calculate the drag force experienced by an infinitely massive quark
propagating at constant velocity through an anisotropic, strongly coupled N=4
plasma by means of its gravity dual. We find that the gluon cloud trailing
behind the quark is generally misaligned with the quark velocity, and that the
latter is also misaligned with the force. The drag coefficient can be
larger or smaller than the corresponding isotropic value depending on the
velocity and the direction of motion. In the ultra-relativistic limit we find
that generically . We discuss the conditions under which this
behaviour may extend to more general situations.Comment: 25 pages, 13 figures; v2: minor changes, added reference
A theory of first order dissipative superfluid dynamics
We determine the most general form of the equations of relativistic
superfluid hydrodynamics consistent with Lorentz invariance, time-reversal
invariance, the Onsager principle and the second law of thermodynamics at first
order in the derivative expansion. Once parity is violated, either because the
symmetry is anomalous or as a consequence of a different parity-breaking
mechanism, our results deviate from the standard textbook analysis of
superfluids. Our general equations require the specification of twenty
parameters (such as the viscosity and conductivity). In the limit of small
relative superfluid velocities we find a seven parameter set of equations. In
the same limit, we have used the AdS/CFT correspondence to compute the parity
odd contributions to the superfluid equations of motion for a generic
holographic model and have verified that our results are consistent.Comment: v1: 84+1 pages; v2: a sign error corrected, and the assumption of
time-reversal invariance made explici