6,685 research outputs found
More Holographic Berezinskii-Kosterlitz-Thouless Transitions
We find two systems via holography that exhibit quantum
Berezinskii-Kosterlitz-Thouless (BKT) phase transitions. The first is the ABJM
theory with flavor and the second is a flavored (1,1) little string theory. In
each case the transition occurs at nonzero density and magnetic field. The BKT
transition in the little string theory is the first example of a quantum BKT
transition in (3+1) dimensions. As in the "original" holographic BKT transition
in the D3/D5 system, the exponential scaling is destroyed at any nonzero
temperature and the transition becomes second order. Along the way we construct
holographic renormalization for probe branes in the ABJM theory and propose a
scheme for the little string theory. Finally, we obtain the embeddings and
(half of) the meson spectrum in the ABJM theory with massive flavor.Comment: 24 pages, 5 figure
Improving the Excited Nucleon Spectrum in Hard-Wall AdS/QCD
We show that the nucleon spectrum in a hard-wall AdS/QCD model can be
improved by use of a relatively large IR cutoff. All of the spin-1/2 nucleon
masses listed in PDG can be fit quite well within 11%. The average error is
remarkably only 4.66%.Comment: 11 pages, 2 figures. v2: references added. v3: add a section about
the pion-nucleon coupling, published versio
Homological perturbation theory for nonperturbative integrals
We use the homological perturbation lemma to produce explicit formulas
computing the class in the twisted de Rham complex represented by an arbitrary
polynomial. This is a non-asymptotic version of the method of Feynman diagrams.
In particular, we explain that phenomena usually thought of as particular to
asymptotic integrals in fact also occur exactly: integrals of the type
appearing in quantum field theory can be reduced in a totally algebraic fashion
to integrals over an Euler--Lagrange locus, provided this locus is understood
in the scheme-theoretic sense, so that imaginary critical points and
multiplicities of degenerate critical points contribute.Comment: 22 pages. Minor revisions from previous versio
Heavy Quark Potential at Finite Temperature Using the Holographic Correspondence
We revisit the calculation of a heavy quark potential in N =4 supersymmetric
Yang-Mills theory at finite temperature using the AdS/CFT correspondence. As is
widely known, the potential calculated in the pioneering works of Rey et al.
and Brandhuber et al. is zero for separation distances r between the quark and
the anti-quark above a certain critical separation, at which the potential has
a kink. We point out that by analytically continuing the string configurations
into the complex plane, and using a slightly different renormalization
subtraction, one obtains a smooth non-zero (negative definite) potential
without a kink. The obtained potential also has a non-zero imaginary
(absorptive) part for separations r > r_c = 0.870/\pi T . At large separations
r the real part of the potential does not exhibit the exponential Debye falloff
expected from perturbation theory and instead falls off as a power law,
proportional to 1/r^4 for r > r_0 = 2.702 / \pi T.Comment: 5 pages, 3 figures. Title modified. Discussion extended and
references modifie
Topological Gravity versus Supergravity on Manifolds with Special Holonomy
We construct a topological theory for euclidean gravity in four dimensions,
by enforcing self-duality conditions on the spin connection. The corresponding
topological symmetry is associated to the SU(2) X diffeomorphism X U(1)
invariance. The action of this theory is that of d=4, N=2 supergravity, up to a
twist. The topological field theory is SU(2) invariant, but the full SO(4)
invariance is recovered after untwist. This suggest that the topological
gravity is relevant for manifolds with special holonomy. The situation is
comparable to that of the topological Yang-Mills theory in eight dimensions,
for which the SO(8) invariance is broken down to Spin(7), but is recovered
after untwisting the topological theory.Comment: LateX file, 19 page
Holography and Unquenched Quark-Gluon Plasmas
We employ the string/gauge theory correspondence to study properties of
strongly coupled quark-gluon plasmas in thermal gauge theories with a large
number of colors and flavors. In particular, we analyze non-critical string
duals of conformal (S)QCD, as well as ten dimensional wrapped fivebrane duals
of SQCD-like theories. We study general properties of the dual plasmas,
including the drag force exerted on a probe quark and the jet quenching
parameter. We find that these plasma observables depend on the number of colors
and flavors in the ``QCD dual''; in particular, we find that the jet quenching
parameter increases linearly with N_f/N_c at leading order in the probe limit.
In the ten dimensional case we find a non trivial drag coefficient but a
vanishing jet quenching parameter. We comment on the relation of this result
with total screening and argue that the same features are shared by all known
plasmas dual to fivebranes in ten dimensions. We also construct new D5 black
hole solutions with spherical horizon and show that they exhibit the same
features.Comment: 30 pages. v2: Comments in section 2 and references updated, a typo
fixe
Black holes in asymptotically Lifshitz spacetimes with arbitrary critical exponent
Recently, a class of gravitational backgrounds in 3+1 dimensions have been
proposed as holographic duals to a Lifshitz theory describing critical
phenomena in 2+1 dimensions with critical exponent . We numerically
explore black holes in these backgrounds for a range of values of . We find
drastically different behavior for and
() the Lifshitz fixed point is repulsive (attractive) when going to larger
radial parameter . For the repulsive backgrounds, we find a continuous
family of black holes satisfying a finite energy condition. However, for
we find that the finite energy condition is more restrictive, and we expect
only a discrete set of black hole solutions, unless some unexpected
cancellations occur. For all black holes, we plot temperature as a function
of horizon radius . For we find that this curve
develops a negative slope for certain values of possibly indicating a
thermodynamic instability.Comment: 23 pages, 6 figures, references corrected, graphs made readable in
greyscal
Compressible quantum phases from conformal field theories in 2+1 dimensions
Conformal field theories (CFTs) with a globally conserved U(1) charge Q can
be deformed into compressible phases by modifying their Hamiltonian, H, by a
chemical potential H -> H - \mu Q. We study 2+1 dimensional CFTs upon which an
explicit S duality mapping can be performed. We find that this construction
leads naturally to compressible phases which are superfluids, solids, or
non-Fermi liquids which are more appropriately called `Bose metals' in the
present context. The Bose metal preserves all symmetries and has Fermi surfaces
of gauge-charged fermions, even in cases where the parent CFT can be expressed
solely by bosonic degrees of freedom. Monopole operators are identified as
order parameters of the solid, and the product of their magnetic charge and Q
determines the area of the unit cell. We discuss implications for holographic
theories on asymptotically AdS4 spacetimes: S duality and monopole/dyon fields
play important roles in this connection.Comment: 30 pages, 2 figures; (v2) small corrections and more ref
Compressing nearly hard sphere fluids increases glass fragility
We use molecular dynamics to investigate the glass transition occurring at
large volume fraction, phi, and low temperature, T, in assemblies of soft
repulsive particles. We find that equilibrium dynamics in the (phi, T) plane
obey a form of dynamic scaling in the proximity of a critical point at T=0 and
phi=phi_0, which should correspond to the ideal glass transition of hard
spheres. This glass point, `point G', is distinct from athermal jamming
thresholds. A remarkable consequence of scaling behaviour is that the dynamics
at fixed phi passes smoothly from that of a strong glass to that of a very
fragile glass as phi increases beyond phi_0. Correlations between fragility and
various physical properties are explored.Comment: 5 pages, 3 figures; Version accepted at Europhys. Let
Near Zone Navier-Stokes Analysis of Heavy Quark Jet Quenching in an =4 SYM Plasma
The near zone energy-momentum tensor of a supersonic heavy quark jet moving
through a strongly-coupled SYM plasma is analyzed in terms of
first-order Navier-Stokes hydrodynamics. It is shown that the hydrodynamical
description of the near quark region worsens with increasing quark velocities.
For realistic quark velocities, , the non-hydrodynamical region is
located at a narrow band surrounding the quark with a width of approximately
in the direction parallel to the quark's motion and with a length of
roughly in the perpendicular direction. Our results can be
interpreted as an indication of the presence of coherent Yang-Mills fields
where deviation from hydrodynamics is at its maximum. In the region where
hydrodynamics does provide a good description of the system's dynamics, the
flow velocity is so small that all the nonlinear terms can be dropped. Our
results, which are compatible with the thermalization timescales extracted from
elliptic flow measurements, suggest that if AdS/CFT provides a good description
of the RHIC system, the bulk of the quenched jet energy has more than enough
time to locally thermalize and become encoded in the collective flow. The
resulting flow pattern close to the quark, however, is shown to be considerably
different than the superposition of Mach cones and diffusion wakes observed at
large distances.Comment: new revised version, 11 figures, as published in PR
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