70 research outputs found
On holography for (pseudo-)conformal cosmology
We propose a holographic dual for (pseudo-)conformal cosmological scenario,
with a scalar field that forms a moving domain wall in adS_5. The domain wall
separates two vacua with unequal energy densities. Unlike in the existing
construction, the 5d solution is regular in the relevant space-time domain.Comment: 6 pages, 1 figur
Gravity waves from inflating brane or Mirrors moving in adS
We study tensor perturbations in a model with inflating Randall--Sundrum-type
brane embedded in five-dimensional anti-de Sitter (adS) bulk. In this
model, a natural {\it in}-vacuum of gravitons is the vacuum defined in static
adS frame. We show that this vacuum is, in fact, the same as the {\it
in}-vacuum defined in the frame with de Sitter (dS) slicing, in which the
brane is at rest. Thus, during inflation, gravitons on and off the brane remain
in their vacuum state. We then study graviton creation by the brane on which
inflation terminates at some moment of time. We mostly consider gravitons whose
wavelengths at the end of inflation exceed both the horizon size and the
adS radius. Creation of these gravitons is dominated by (zero mode)--(zero
mode) Bogoliubov coefficients and, apart from an overall factor, the spectrum
of produced gravitons is the same as in four-dimensional theory.
``Kaluza--Klein'' gravitons are also produced, but this effect is subdominant.
Graviton spectra at somewhat higher momenta are also presented for
completeness.Comment: 33 pages, 1 figur
Higgs inflation: consistency and generalisations
We analyse the self-consistency of inflation in the Standard Model, where the
Higgs field has a large non-minimal coupling to gravity. We determine the
domain of energies in which this model represents a valid effective field
theory as a function of the background Higgs field. This domain is bounded
above by the cutoff scale which is found to be higher than the relevant
dynamical scales throughout the whole history of the Universe, including the
inflationary epoch and reheating. We present a systematic scheme to take into
account quantum loop corrections to the inflationary calculations within the
framework of effective field theory. We discuss the additional assumptions that
must be satisfied by the ultra-violet completion of the theory to allow
connection between the parameters of the inflationary effective theory and
those describing the low-energy physics relevant for the collider experiments.
A class of generalisations of inflationary theories with similar properties is
constructed.Comment: 25 pages, 1 figur
Cosmological constraints on deviations from Lorentz invariance in gravity and dark matter
We consider a scenario where local Lorentz invariance is violated by the
existence of a preferred time direction at every space-time point. This
scenario can arise in the context of quantum gravity and its description at low
energies contains a unit time-like vector field which parameterizes the
preferred direction. The particle physics tests of Lorentz invariance preclude
a direct coupling of this vector to the fields of the Standard Model, but do
not bear implications for dark matter. We discuss how the presence of this
vector and its possible coupling to dark matter affect the evolution of the
Universe. At the level of homogeneous cosmology the only effect of Lorentz
invariance violation is a rescaling of the expansion rate. The physics is
richer at the level of perturbations. We identify three effects crucial for
observations: the rescaling of the matter contribution to the Poisson equation,
the appearance of an extra contribution to the anisotropic stress and the
scale-dependent enhancement of dark matter clustering. These effects result in
distinctive features in the power spectra of the CMB and density fluctuations.
Making use of the data from Planck and WiggleZ we obtain the most stringent
cosmological constraints to date on departures from Lorentz symmetry. Our
analysis provides the first direct bounds on deviations from Lorentz invariance
in the dark matter sector.Comment: 10 pages, 3 figures, revtex; footnote on isocurvature modes added,
discussion on the decoupling of the Standard Model fields from the aether
extended, a reference added; version to be published in JCA
Gauge theory solitons on noncommutative cylinder
We generalize to noncommutative cylinder the solution generation technique,
originally suggested for gauge theories on noncommutative plane. For this
purpose we construct partial isometry operators and complete set of orthogonal
projectors in the algebra of the cylinder, and an isomorphism between the free
module and its direct sum with the Fock module on the cylinder. We construct
explicitly the gauge theory soliton and evaluate the spectrum of perturbations
about this soliton.Comment: References added; to appear in Theor.Math.Phy
Unstable Semiclassical Trajectories in Tunneling
Some tunneling phenomena are described, in the semiclassical approximation,
by unstable complex trajectories. We develop a systematic procedure to
stabilize the trajectories and to calculate the tunneling probability,
including both the suppression exponent and prefactor. We find that the
instability of tunneling solutions modifies the power-law dependence of the
prefactor on h as compared to the case of stable solutions.Comment: Journal version; 4 pages, 2 figure
Self-accelerated brane Universe with warped extra dimension
We propose a cosmological model which exhibits the phenomenon of
self-acceleration: the Universe is attracted to the phase of accelerated
expansion at late times even in the absence of the cosmological constant. The
self-acceleration is inevitable in the sense that it cannot be neutralized by
any negative explicit cosmological constant. The model is formulated in the
framework of brane-world theories with a warped extra dimension. The key
ingredient of the model is the brane-bulk energy transfer which is carried by
bulk vector fields with a sigma-model-like boundary condition on the brane. We
explicitly find the 5-dimensional metric corresponding to the late-time de
Sitter expansion on the brane; this metric describes an AdS_5 black hole with
growing mass. The present value of the Hubble parameter implies the scale of
new physics of order 1 TeV, where the proposed model has to be replaced by
putative UV-completion. The mechanism leading to the self-acceleration has
AdS/CFT interpretation as occurring due to specific dynamics of conformal
matter interacting with external "electric" fields. The Universe expansion
history predicted by the model is distinguishable from the standard LambdaCDM
cosmology.Comment: 32 pages, 2 figure
Complex trajectories in chaotic dynamical tunneling
We develop the semiclassical method of complex trajectories in application to chaotic dynamical tunneling. First, we suggest a systematic numerical technique for obtaining complex tunneling trajectories by the gradual deformation of the classical ones. This provides a natural classification of the tunneling solutions. Second, we present a heuristic procedure for sorting out the least suppressed trajectory. As an illustration, we apply our technique to the process of chaotic tunneling in a quantum mechanical model with two degrees of freedom. Our analysis reveals rich dynamics of the system. At the classical level, there exists an infinite set of unstable solutions forming a fractal structure. This structure is inherited by the complex tunneling paths and plays the central role in the semiclassical study. The process we consider exhibits the phenomenon of optimal tunneling: the suppression exponent of the tunneling probability has a local minimum at a certain energy which is thus (locally) the optimal energy for tunneling. We test the proposed method by comparison of the semiclassical results with the results of the exact quantum computations and find a good agreement
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