17 research outputs found
Axion-like-particle search with high-intensity lasers
We study ALP-photon-conversion within strong inhomogeneous electromagnetic
fields as provided by contemporary high-intensity laser systems. We observe
that probe photons traversing the focal spot of a superposition of Gaussian
beams of a single high-intensity laser at fundamental and frequency-doubled
mode can experience a frequency shift due to their intermittent propagation as
axion-like-particles. This process is strongly peaked for resonant masses on
the order of the involved laser frequencies. Purely laser-based experiments in
optical setups are sensitive to ALPs in the mass range and can
thus complement ALP searches at dipole magnets.Comment: 25 pages, 2 figure
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Small dark energy and stable vacuum from DilatonâGaussâBonnet coupling in TMT
Abstract In two measures theories (TMT), in addition to the Riemannian measure of integration, being the square root of the determinant of the metric, we introduce a metric-independent density ÎŚ in four dimensions defined in terms of scalars Ď a by ÎŚ = Îľ Îź ν Ď Ď Îľ a b c d ( â Îź Ď a ) ( â ν Ď b ) ( â Ď Ď c ) ( â Ď Ď d ) . With the help of a dilaton field Ď we construct theories that are globally scale invariant. In particular, by introducing couplings of the dilaton Ď to the GaussâBonnet (GB) topological density - g Ď R Îź ν Ď Ď 2 - 4 R Îź ν 2 + R 2 we obtain a theory that is scale invariant up to a total divergence. Integration of the Ď a field equation leads to an integration constant that breaks the global scale symmetry. We discuss the stabilizing effects of the coupling of the dilaton to the GB-topological density on the vacua with a very small cosmological constant and the resolution of the âTMT Vacuum-Manifold Problemâ which exists in the zero cosmological-constant vacuum limit. This problem generically arises from an effective potential that is a perfect square, and it gives rise to a vacuum manifold instead of a unique vacuum solution in the presence of many different scalars, like the dilaton, the Higgs, etc. In the non-zero cosmological-constant case this problem disappears. Furthermore, the GB coupling to the dilaton eliminates flat directions in the effective potential, and it totally lifts the vacuum-manifold degeneracy
The dark side of the torsion: dark energy from propagating torsion
An extension to the Einstein-Cartan (EC) action is discussed in terms of
cosmological solutions. The torsion incorporated in the EC Lagrangian is
assumed to be totally anti-symmetric, represented by a time-like axial vector
. The dynamics of torsion is invoked by a novel kinetic term. Here we
show that this kinetic term gives rise to dark energy, while the quadratic
torsion term, emanating from the EC part, represents a stiff fluid that leads
to a bouncing cosmology solution. A constraint on the bouncing solution is
calculated using cosmological data from different epochs
Equivalent off-diagonal cosmological models and ekpyrotic scenarios in f ( R ) -modified, massive, and einstein gravity
We re-investigate how generic off-diagonal cosmological solutions depending,
in general, on all spacetime coordinates can be constructed in massive and
f-modified gravity using the anholonomic frame deformation method. There are
constructed new classes of locally anisotropic and (in) homogeneous
cosmological metrics with open and closed spatial geometries. By resorting such
solutions, we show that they describe the late time acceleration due to
effective cosmological terms induced by nonlinear off-diagonal interactions,
possible modifications of the gravitational action and graviton mass. The
cosmological metrics and related St\" uckelberg fields are constructed in
explicit form up to nonholonomic frame transforms of the
Friedmann-Lama\^{\i}tre-Robertson-Walker (FLRW) coordinates. The solutions
include matter, graviton mass and other effective sources modelling nonlinear
gravitational and matter fields interactions with polarization of physical
constants and deformations of metrics, which may explain dark energy and dark
matter effects. However, we argue that it is not obligatory always to modify
gravity if we consider effective generalized Einstein equations with nontrivial
vacuum and/or non-minimal coupling with matter. Indeed, we state certain
conditions when such configurations mimic interesting solutions in general
relativity and modifications, for instance, when we can extract the general
Painlev\' e-Gullstrand and FLRW metrics. In a more general context, we
elaborate on a reconstruction procedure for off-diagonal cosmological solutions
which describe cyclic and ekpyrotic universes. Finally, there are discussed
open issues and further perspectives.Comment: 16 pages, latex2e; it is a regular article variant extended and
modified following requests of the Editor and accepted by EPJC; this version
contains new results and details comparing to the letter variant
arXiv:1304.108