111 research outputs found
Horava-Lifshitz Gravity From Dynamical Newton-Cartan Geometry
Recently it has been established that torsional Newton-Cartan (TNC) geometry
is the appropriate geometrical framework to which non-relativistic field
theories couple. We show that when these geometries are made dynamical they
give rise to Horava-Lifshitz (HL) gravity. Projectable HL gravity corresponds
to dynamical Newton-Cartan (NC) geometry without torsion and non-projectable HL
gravity corresponds to dynamical NC geometry with twistless torsion
(hypersurface orthogonal foliation). We build a precise dictionary relating all
fields (including the scalar khronon), their transformations and other
properties in both HL gravity and dynamical TNC geometry. We use TNC invariance
to construct the effective action for dynamical twistless torsional
Newton-Cartan geometries in 2+1 dimensions for dynamical exponent 1<z\le 2 and
demonstrate that this exactly agrees with the most general forms of the HL
actions constructed in the literature. Further, we identify the origin of the
U(1) symmetry observed by Horava and Melby-Thompson as coming from the Bargmann
extension of the local Galilean algebra that acts on the tangent space to TNC
geometries. We argue that TNC geometry, which is manifestly diffeomorphism
covariant, is a natural geometrical framework underlying HL gravity and discuss
some of its implications.Comment: 48 page
Schroedinger Invariance from Lifshitz Isometries in Holography and Field Theory
We study non-relativistic field theory coupled to a torsional Newton-Cartan
geometry both directly as well as holographically. The latter involves gravity
on asymptotically locally Lifshitz space-times. We define an energy-momentum
tensor and a mass current and study the relation between conserved currents and
conformal Killing vectors for flat Newton-Cartan backgrounds. It is shown that
flat NC space-time realizes two copies of the Lifshitz algebra that together
form a Schroedinger algebra (without the central element). We show why the
Schroedinger scalar model has both copies as symmetries and the Lifshitz scalar
model only one. Finally we discuss the holographic dual of this phenomenon by
showing that the bulk Lifshitz space-time realizes the same two copies of the
Lifshitz algebra.Comment: 5 pages, modified abstract, clarifications added, typos fixed, refs
update
Extremal Black Hole Horizons
Using the blackfold effective theory applied to extremal Kerr branes we
provide evidence for the existence of new stationary extremal black hole
solutions in asymptotically flat spacetime with both single and multiple
disconnected horizons. These include extremal doubly-spinning black rings,
black saturns, di-rings and bi-rings in five spacetime dimensions as well as
extremal Myers-Perry black holes and black saturns in dimensions greater than
five. Some of these constructions constitute the first examples of black hole
solutions with extremal disconnected horizons in vacuum Einstein gravity.Comment: v2: 30pp, 12 figures; comments and reference added; comparison
between approximate and analytic black ring and Myers-Perry solutions added;
to be published in JHE
Electroelasticity of Charged Black Branes
We present the first-order corrected dynamics of fluid branes carrying
higher-form charge by obtaining the general form of their equations of motion
to pole-dipole order. Assuming linear response theory, we characterize the
corresponding effective theory of stationary bent charged (an)isotropic fluid
branes in terms of two sets of response coefficients, the Young modulus and the
piezoelectric moduli. We subsequently find large classes of examples in gravity
of this effective theory, by constructing stationary strained charged black
brane solutions to first order in a derivative expansion. Using solution
generating techniques and bent neutral black branes as a seed solution, we
obtain a class of charged black brane geometries carrying smeared Maxwell
charge in Einstein-Maxwell-dilaton gravity. In the specific case of
ten-dimensional space-time we furthermore use T-duality to generate bent black
branes with higher-form charge, including smeared D-branes of type II string
theory. By subsequently measuring the bending moment and the electric dipole
moment which these geometries acquire due to the strain, we uncover that their
form is captured by classical electroelasticity theory. In particular, we find
that the Young modulus and the piezoelectric moduli of our strained charged
black brane solutions are parameterized by a total of 4 response coefficients,
both for the isotropic as well as anisotropic cases.Comment: v2: 40pp; typos fixe
Observational signature of near-extremal Kerr-like black holes in a modified gravity theory at the Event Horizon Telescope
We study the shadows cast by near-extremal Kerr-MOG black holes for different
values of the parameter in modified gravity (MOG). In particular, we consider
an isotropic emitter orbiting near such black holes and analytically compute
the positions, fluxes and redshift factors of their images. The size of the
shadow decreases when the modified parameter is increased. For each shadow, the
images of the emitter appear on a special part of the shadow which has a rich
structure. The primary image and secondary images are similar to those produced
for the near-extremal (high spin) Kerr black hole, but the near-extremal
Kerr-MOG black hole can have a spin () which is finitely
lower than 1. When the modified parameter is varied, the typical positions of
the corresponding images do not change, nor does the typical redshift factor
associated with the primary image. However, another typical redshift factor
associated with the secondary image increases when the modified parameter is
increased. We also find that the fluxes increase in that case. These images
appear periodically with period greater than that of Kerr. This provides an
alternative signature away from the Kerr case which may be tested by the Event
Horizon Telescope.Comment: 16 pages, 5 figures and 1 table. Slight change in title , fixed
typos, added references. Published in PR
Stable Non-Supersymmetric Vacua in the Moduli Space of Non-Critical Superstrings
We study a set of asymmetric deformations of non-critical superstring
theories in various dimensions. The deformations arise as Kaehler and complex
structure deformations of an orthogonal two-torus comprising of a parallel and
a transverse direction in the near-horizon geometry of NS5-branes. The
resulting theories have the following intriguing features: Spacetime
supersymmetry is broken in a continuous fashion and the masses of the lightest
modes are lifted. In particular, no bulk or localized tachyons are generated in
the non-supersymmetric vacua. We discuss the effects of these deformations in
the context of the holographic duality between non-critical superstrings and
Little String Theories and find solutions of rotating fivebranes in
supergravity. We also comment on the generation of a one-loop cosmological
constant and determine the effects of the one-loop backreaction to leading
order.Comment: lanlmac, 41 pages, 1 figure; v2 an erroneous statement corrected in
section 6, version published in NP
Field Theory on Newton-Cartan Backgrounds and Symmetries of the Lifshitz Vacuum
Holography for Lifshitz space-times corresponds to dual field theories on a
fixed torsional Newton-Cartan (TNC) background. We examine the coupling of
non-relativistic field theories to TNC backgrounds and uncover a novel
mechanism by which a global U(1) can become local. This involves the TNC vector
which sources a particle number current, and which for flat NC
space-time satisfies with a Schroedinger symmetry
realized on . We discuss various toy model field theories on flat NC
space-time for which the new mechanism leads to extra global space-time
symmetries beyond the generic Lifshitz symmetry, allowing for an enhancement to
Schroedinger symmetry. On the holographic side, the source also appears in
the Lifshitz vacuum with exactly the same properties as for flat NC space-time.
In particular, the bulk diffeomorphisms that preserve the boundary conditions
realize a Schroedinger algebra on , allowing for a conserved particle number
current. Finally, we present a probe action for a complex scalar field on the
Lifshitz vacuum, which exhibits Schroedinger invariance in the same manner as
seen in the field theory models.Comment: 55 pages + 2 appendice
Null-Wave Giant Gravitons from Thermal Spinning Brane Probes
We construct and analyze thermal spinning giant gravitons in type II/M-theory
based on spherically wrapped black branes, using the method of thermal probe
branes originating from the blackfold approach. These solutions generalize in
different directions recent work in which the case of thermal (non-spinning)
D3-brane giant gravitons was considered, and reveal a rich phase structure with
various new properties. First of all, we extend the construction to M-theory,
by constructing thermal giant graviton solutions using spherically wrapped M2-
and M5-branes. More importantly, we switch on new quantum numbers, namely
internal spins on the sphere, which are not present in the usual extremal limit
for which the brane world volume stress tensor is Lorentz invariant. We examine
the effect of this new type of excitation and in particular analyze the
physical quantities in various regimes, including that of small temperatures as
well as low/high spin. As a byproduct we find new stationary dipole-charged
black hole solutions in AdS_m X S^n backgrounds of type II/M-theory. We finally
show, via a double scaling extremal limit, that our spinning thermal giant
graviton solutions lead to a novel null-wave zero-temperature giant graviton
solution with a BPS spectrum, which does not have an analogue in terms of the
conventional weakly coupled world volume theory.Comment: v1: 31p
Holographic Models for Theories with Hyperscaling Violation
We study in detail a variety of gravitational toy models for
hyperscaling-violating Lifshitz (hvLif) space-times. These space-times have
been recently explored as holographic dual models for condensed matter systems.
We start by considering a model of gravity coupled to a massive vector field
and a dilaton with a potential. This model supports the full class of hvLif
space-times and special attention is given to the particular values of the
scaling exponents appearing in certain non-Fermi liquids. We study linearized
perturbations in this model, and consider probe fields whose interactions mimic
those of the perturbations. The resulting equations of motion for the probe
fields are invariant under the Lifshitz scaling. We derive
Breitenlohner-Freedman-type bounds for these new probe fields. For the cases of
interest the hvLif space-times have curvature invariants that blow up in the
UV. We study the problem of constructing models in which the hvLif space-time
can have an AdS or Lifshitz UV completion. We also analyze reductions of
Schroedinger space-times and reductions of waves on extremal (intersecting)
branes, accompanied by transverse space reductions, that are solutions to
supergravity-like theories, exploring the allowed parameter range of the hvLif
scaling exponents.Comment: version 3: matches published versio
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