252 research outputs found
More about spontaneous Lorentz-violation and infrared modification of gravity
We consider a model with Lorentz-violating vector field condensates, in which
dispersion laws of all perturbations, including tensor modes, undergo
non-trivial modification in the infrared. The model is free of ghosts and
tachyons at high 3-momenta. At low 3-momenta there are ghosts, and at even
lower 3-momenta there exist tachyons. Still, with appropriate choice of
parameters, the model is phenomenologically acceptable. Beyond a certain large
distance scale and even larger time scale, the gravity of a static source
changes from that of General Relativity to that of van Dam--Veltman--Zakharov
limit of the Fierz--Pauli theory. Yet the late time cosmological evolution is
always determined by the standard Friedmann equation, modulo small correction
to the ``cosmological Planck mass'', so the modification of gravity cannot by
itself explain the accelerated expansion of the Universe. We argue that the
latter property is generic in a wide class of models with condensates.Comment: 15 pages, 1 figure, JHEP3.cls; Added reference
Quasi-localized states on noncommutative solitons
We consider noncommutative gauge theories which have zero mass states
propagating along both commutative and noncommutative dimensions. Solitons in
these theories generically carry U(m) gauge group on their world-volume. From
the point of view of string theory, these solitons correspond to
``branes within branes''. We show that once the world-volume U(m) gauge
theory is in the Higgs phase, light states become quasi-localized, rather than
strictly localized on the soliton, i.e. they mix with light bulk modes and have
finite widths to escape into the noncommutative dimensions. At small values of
U(m) symmetry breaking parameters, these widths are small compared to the
corresponding masses. Explicit examples considered are adjoint scalar field in
the background of a noncommutative vortex in U(1)-Higgs theory, and gauge
fields in instanton backgrounds in pure gauge noncommutative theories.Comment: 27 pages, references and comments added, final version to appear in
JHE
Ultra-large distance modification of gravity from Lorentz symmetry breaking at the Planck scale
We present an extension of the Randall--Sundrum model in which, due to
spontaneous Lorentz symmetry breaking, graviton mixes with bulk vector fields
and becomes quasilocalized. The masses of KK modes comprising the
four-dimensional graviton are naturally exponentially small. This allows to
push the Lorentz breaking scale to as high as a few tenth of the Planck mass.
The model does not contain ghosts or tachyons and does not exhibit the van
Dam--Veltman--Zakharov discontinuity. The gravitational attraction between
static point masses becomes gradually weaker with increasing of separation and
gets replaced by repulsion (antigravity) at exponentially large distances.Comment: 28 page
Creating semiclassical black holes in collider experiments and keeping them on a string
We argue that a simple modification of the TeV scale quantum gravity scenario
allows production of semiclassical black holes in particle collisions at the
LHC. The key idea is that in models with large extra dimensions the strength of
gravity in the bulk can be higher than on the brane where we live. A well-known
example of this situation is the case of warped extra dimensions. Even if the
energy of the collision is not sufficient to create a black hole on the brane,
it may be enough to produce a particle which accelerates into the bulk up to
trans-Planckian energy and creates a large black hole there. In a concrete
model we consider, the black hole is formed in a collision of the particle with
its own image at an orbifold plane. When the particle in question carries some
Standard Model gauge charges the created black hole gets attached to our brane
by a string of the gauge flux. For a 4-dimensional observer such system looks
as a long-lived charged state with the mass continuously decreasing due to
Hawking evaporation of the black hole. This provides a distinctive signature of
black hole formation in our scenario.Comment: Journal version, a misprint correcte
QED from six-dimensional vortex and gauge anomalies
Starting from an anomaly-free Abelian Higgs model coupled to gravity in a
6-dimensional space-time we construct an effective four-dimensional theory of
charged fermions interacting with U(1) Abelian gauge field and gravity, both
localised near the core of a Nielsen-Olesen vortex configuration. We show that
an anomaly free theory in 6-dimensions can give rise to an anomalous theory in
D=4, which suggests a possibility of consistent regularisation of abelian
anomalous chiral gauge theories in four dimensions. We also show that the
spectrum of charged bulk fermions has a mass gap.Comment: Latex, 19 page
Prospects for sgoldstino search at the LHC
In this paper we estimate the LHC sgoldstino discovery potential for the
signatures with gamma gamma and ZZ in a final state.Comment: 12 pages, 12 figures; journal version: minor change
Bumpy black holes from spontaneous Lorentz violation
We consider black holes in Lorentz violating theories of massive gravity. We
argue that in these theories black hole solutions are no longer universal and
exhibit a large number of hairs. If they exist, these hairs probe the
singularity inside the black hole providing a window into quantum gravity. The
existence of these hairs can be tested by future gravitational wave
observatories. We generically expect that the effects we discuss will be larger
for the more massive black holes. In the simplest models the strength of the
hairs is controlled by the same parameter that sets the mass of the graviton
(tensor modes). Then the upper limit on this mass coming from the inferred
gravitational radiation emitted by binary pulsars implies that hairs are likely
to be suppressed for almost the entire mass range of the super-massive black
holes in the centers of galaxies.Comment: 40 pages, 4 figure
Comment on 4D Lorentz invariance violations in the brane-world
The brane-world scenario offers the possibility for signals to travel outside
our visible universe and reenter it. We find the condition for a signal emitted
from the brane to return to the brane. We study the propagation of such signals
and show that, as seen by a 4D observer, these signals arrive earlier than
light traveling along the brane. We also study the horizon problem and find
that, while the bulk signals can travel far enough to homogenize the visible
universe, it is unlikely that they have a significant effect since they are
redshifted in the gravitational field of the bulk black hole.Comment: 21 pages, 6 figures, REVTEX, New section adde
Spontaneous breaking of Lorentz invariance, black holes and perpetuum mobile of the 2nd kind
We study the effect of spontaneous breaking of Lorentz invariance on black
hole thermodynamics. We consider a scenario where Lorentz symmetry breaking
manifests itself by the difference of maximal velocities attainable by
particles of different species in a preferred reference frame. The Lorentz
breaking sector is represented by the ghost condensate. We find that the
notions of black hole entropy and temperature loose their universal meaning. In
particular, the standard derivation of the Hawking radiation yields that a
black hole does emit thermal radiation in any given particle species, but with
temperature depending on the maximal attainable velocity of this species. We
demonstrate that this property implies violation of the second law of
thermodynamics, and hence, allows construction of a perpetuum mobile of the 2nd
kind. We discuss possible interpretation of these results.Comment: 13 pages; references adde
Non-renormalization of induced charges and constraints on strongly coupled theories
It is shown that global fermionic charges induced in vacuum by slowly
varying, topologically non-trivial background scalar fields are not
renormalized provided that expansion in momenta of background fields is valid.
This suggests that strongly coupled theories obey induced charge matching
conditions which are analogous, but generally not equivalent, to 't Hooft
anomaly matching conditions. We give a few examples of induced charge matching.
In particular, the corresponding constraints in softly broken supersymmetric
QCD suggest non-trivial low energy mass pattern, in full accord with the
results of direct analyses.Comment: 19 pages, LaTeX, two PS figures; Submitted to special issue of Phys.
Reports dedicated to 70th birthday of L.B.Oku
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