65 research outputs found
Constraints on RG Flows from Holographic Entanglement Entropy
We examine the RG flow of a candidate c-function, extracted from the
holographic entanglement entropy of a strip-shaped region, for theories with
broken Lorentz invariance. We clarify the conditions on the geometry that lead
to a break-down of monotonic RG flows as is expected for generic
Lorentz-violating field theories. Nevertheless we identify a set of simple
criteria on the UV behavior of the geometry which guarantee a monotonic
c-function. Our analysis can thus be used as a guiding principle for the
construction of monotonic RG trajectories, and can also prove useful for
excluding possible IR behaviors of the theory.Comment: 5 pages, no figure
Criteria For Superfluid Instabilities of Geometries with Hyperscaling Violation
We examine the onset of superfluid instabilities for geometries that exhibit
hyperscaling violation and Lifshitz-like scaling at infrared and intermediate
energy scales, and approach AdS in the ultraviolet. In particular, we are
interested in the role of a non-trivial coupling between the neutral scalar
supporting the scaling regime, and the (charged) complex scalar which
condenses. The analysis focuses exclusively on unstable modes arising from the
hyperscaling-violating portion of the geometry. Working at zero temperature, we
identify simple analytical criteria for the presence of scalar instabilities,
and discuss under which conditions a minimal charge will be needed to trigger a
transition. Finite temperature examples are constructed numerically for a few
illustrative cases.Comment: 41 pages, 7 figure
Intertwined Orders in Holography: Pair and Charge Density Waves
Building on [1], we examine a holographic model in which a U(1) symmetry and
translational invariance are broken spontaneously at the same time. The
symmetry breaking is realized through the St\"{u}ckelberg mechanism, and leads
to a scalar condensate and a charge density which are spatially modulated and
exhibit unidirectional stripe order. Depending on the choice of parameters, the
oscillations of the scalar condensate can average out to zero, with a frequency
which is half of that of the charge density. In this case the system realizes
some of the key features of pair density wave order. The model also admits a
phase with co-existing superconducting and charge density wave orders, in which
the scalar condensate has a uniform component. In our construction the various
orders are intertwined with each other and have a common origin. The fully
backreacted geometry is computed numerically, including for the case in which
the theory contains axions. The latter can be added to explicitly break
translational symmetry and mimic lattice-type effects.Comment: 37 pages, 17 figure
Correlation Functions and Hidden Conformal Symmetry of Kerr Black Holes
Extremal scalar three-point correlators in the near-NHEK geometry of Kerr
black holes have recently been shown to agree with the result expected from a
holographically dual non-chiral two-dimensional conformal field theory. In this
paper we extend this calculation to extremal three-point functions of scalars
in a general Kerr black hole which need not obey the extremality condition
. It was recently argued that for low frequency scalars in the Kerr
geometry there is a dual conformal field theory description which determines
the interactions in this regime. Our results support this conjecture.
Furthermore, we formulate a recipe for calculating finite-temperature retarded
three-point correlation functions which is applicable to a large class of (even
non-extremal) correlators, and discuss the vanishing of the extremal couplings.Comment: 16 page
Dilaton Dynamics from Production of Tensionless Membranes
In this paper we consider classical and quantum corrections to cosmological
solutions of 11D SUGRA coming from dynamics of membrane states. We first
consider the supermembrane spectrum following the approach of Russo and
Tseytlin for consistent quantization. We calculate the production rate of BPS
membrane bound states in a cosmological background and find that such effects
are generically suppressed by the Planck scale, as expected. However, for a
modified brane spectrum possessing enhanced symmetry, production can be finite
and significant. We stress that this effect could not be anticipated given only
a knowledge of the low-energy effective theory. Once on-shell, inclusion of
these states leads to an attractive force pulling the dilaton towards a fixed
point of S-duality, namely . Although the SUGRA description breaks down
in this regime, inclusion of the enhanced states suggests that the center of
M-theory moduli space is a dynamical attractor. Morever, our results seem to
suggest that string dynamics does indeed favor a vacuum near fixed points of
duality.Comment: 39 pages, 7 figures, minor corrections and reference adde
Backreacted DBI Magnetotransport with Momentum Dissipation
We examine magnetotransport in a holographic Dirac-Born-Infeld model, taking
into account the effects of backreaction on the geometry. The theory we
consider includes axionic scalars, introduced to break translational symmetry
and generate momentum dissipation. The generic structure of the DC conductivity
matrix for these theories is extremely rich, and is significantly more complex
than that obtained in the probe approximation. We find new classes of black
brane solutions, including geometries that exhibit Lifshitz scaling and
hyperscaling violation, and examine their implications on the transport
properties of the system. Depending on the choice of theory parameters, these
backgrounds can lead to metallic or insulating behavior. Negative
magnetoresistance is observed in a family of dynoic solutions. Some of the new
backreacted geometries also support magnetic-field-induced metal-insulator
transitions.Comment: 34 pages, 9 figures; v2: references added, minor improvements, to
appear in JHE
Holographic RG flows with nematic IR phases
We construct zero-temperature geometries that interpolate between a Lifshitz
fixed point in the UV and an IR phase that breaks spatial rotations but
preserves translations. We work with a simple holographic model describing two
massive gauge fields coupled to gravity and a neutral scalar. Our construction
can be used to describe RG flows in non-relativistic, strongly coupled quantum
systems with nematic order in the IR. In particular, when the dynamical
critical exponent of the UV fixed point is z=2 and the IR scaling exponents are
chosen appropriately, our model realizes holographically the scaling properties
of the bosonic modes of the quadratic band crossing model.Comment: 19 pages, 2 figures. References added. Expanded discussion on nematic
orde
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