6,155 research outputs found
Quantization of scalar perturbations in brane-world inflation
We consider a quantization of scalar perturbations about a de Sitter brane in
a 5-dimensional anti-de Sitter (AdS) bulk spacetime. We first derive the second
order action for a master variable for 5-dimensional gravitational
perturbations. For a vacuum brane, there is a continuum of normalizable
Kaluza-Klein (KK) modes with . There is also a light radion mode with
which satisfies the junction conditions for two branes, but is
non-normalizable for a single brane model. We perform the quantization of these
bulk perturbations and calculate the effective energy density of the projected
Weyl tensor on the barne. If there is a test scalar field perturbation on the
brane, the mode together with the zero-mode and an infinite ladder
of discrete tachyonic modes become normalizable in a single brane model. This
infinite ladder of discrete modes as well as the continuum of KK modes with
introduce corrections to the scalar field perturbations at first-order
in a slow-roll expansion. We derive the second order action for the
Mukhanov-Sasaki variable coupled to the bulk perturbations which is needed to
perform the quantization and determine the amplitude of scalar perturbations
generated during inflation on the brane.Comment: 14 page
Ultra cold neutron trap as a tool to search for dark matter with long-range radius of forces
The problem of possible application of an ultracold neutron (UCN) trap as a
detector of dark matter particles with long-range radius of forces has been
considered. Transmission of small recoil energy in scattering is a
characteristic of long-range forces. The main advantage of the ultracold
neutron technique lies in possibility of detecting recoil energy as small as
eV. Here are presented constraints on the interaction potential
parameters: for dark matter particles and
neutrons, as well as on the density value of long-range dark matter on the
Earth. The possible mechanism of accumulation of long-range dark matter on the
Earth surface is considered and the factor of density increase on the Earth
surface is evaluated. The results of the first experiment on search of
astronomical day variation of ultracold neutron storage time are under
discussion.Comment: 17 pages, 19 figures. arXiv admin note: substantial text overlap with
arXiv:1109.339
Primordial perturbations from slow-roll inflation on a brane
In this paper we quantise scalar perturbations in a Randall-Sundrum-type
model of inflation where the inflaton field is confined to a single brane
embedded in five-dimensional anti-de Sitter space-time. In the high energy
regime, small-scale inflaton fluctuations are strongly coupled to metric
perturbations in the bulk and gravitational back-reaction has a dramatic effect
on the behaviour of inflaton perturbations on sub-horizon scales. This is in
contrast to the standard four-dimensional result where gravitational
back-reaction can be neglected on small scales. Nevertheless, this does not
give rise to significant particle production, and the correction to the power
spectrum of the curvature perturbations on super-horizon scales is shown to be
suppressed by a slow-roll parameter. We calculate the complete first order
slow-roll corrections to the spectrum of primordial curvature perturbations.Comment: 23 pages, 10 figure
Exciton correlations in coupled quantum wells and their luminescence blue shift
In this paper we present a study of an exciton system where electrons and
holes are confined in double quantum well structures. The dominating
interaction between excitons in such systems is a dipole - dipole repulsion. We
show that the tail of this interaction leads to a strong correlation between
excitons and substantially affects the behavior of the system. Making use of
qualitative arguments and estimates we develop a picture of the exciton -
exciton correlations in the whole region of temperature and concentration where
excitons exist. It appears that at low concentration degeneracy of the excitons
is accompanied with strong multi-particle correlation so that the system cannot
be considered as a gas. At high concentration the repulsion suppresses the
quantum degeneracy down to temperatures that could be much lower than in a Bose
gas with contact interaction. We calculate the blue shift of the exciton
luminescence line which is a sensitive tool to observe the exciton - exciton
correlations.Comment: 27 pages in PDF and DVI format, 8 figure
Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field
We report on magnetization, sound velocity, and magnetocaloric-effect
measurements of the Ising-like spin-1/2 antiferromagnetic chain system
BaCoVO as a function of temperature down to 1.3 K and applied
transverse magnetic field up to 60 T. While across the N\'{e}el temperature of
K anomalies in magnetization and sound velocity confirm the
antiferromagnetic ordering transition, at the lowest temperature the
field-dependent measurements reveal a sharp softening of sound velocity
and a clear minimum of temperature at T,
indicating the suppression of the antiferromagnetic order. At higher fields,
the curve shows a broad minimum at T, accompanied by a
broad minimum in the sound velocity and a saturation-like magnetization. These
features signal a quantum phase transition which is further characterized by
the divergent behavior of the Gr\"{u}neisen parameter . By contrast, around the critical field, the
Gr\"{u}neisen parameter converges as temperature decreases, pointing to a
quantum critical point of the one-dimensional transverse-field Ising model.Comment: Phys. Rev. Lett., to appea
Spin and magnetization effects in plasmas
We give a short review of a number of different models for treating
magnetization effects in plasmas. In particular, the transition between kinetic
models and fluid models is discussed. We also give examples of applications of
such theories. Some future aspects are discussed.Comment: 18 pages, 1 figure. To appear in Plasma Physics and Controlled
Fusion, Special Issue for the 37th ICPP, Santiago, Chil
The optical depth of the Universe to ultrahigh energy cosmic ray scattering in the magnetized large scale structure
This paper provides an analytical description of the transport of ultrahigh
energy cosmic rays in an inhomogeneously magnetized intergalactic medium. This
latter is modeled as a collection of magnetized scattering centers such as
radio cocoons, magnetized galactic winds, clusters or magnetized filaments of
large scale structure, with negligible magnetic fields in between. Magnetic
deflection is no longer a continuous process, it is rather dominated by
scattering events. We study the interaction between high energy cosmic rays and
the scattering agents. We then compute the optical depth of the Universe to
cosmic ray scattering and discuss the phenomological consequences for various
source scenarios. For typical parameters of the scattering centers, the optical
depth is greater than unity at 5x10^{19}eV, but the total angular deflection is
smaller than unity. One important consequence of this scenario is the
possibility that the last scattering center encountered by a cosmic ray be
mistaken with the source of this cosmic ray. In particular, we suggest that
part of the correlation recently reported by the Pierre Auger Observatory may
be affected by such delusion: this experiment may be observing in part the last
scattering surface of ultrahigh energy cosmic rays rather than their source
population. Since the optical depth falls rapidly with increasing energy, one
should probe the arrival directions of the highest energy events beyond
10^{20}eV on an event by event basis to circumvent this effect.Comment: version to appear in PRD; substantial improvements: extended
introduction, sections added on angular images and on direction dependent
effects with sky maps of optical depth, enlarged discussion of Auger results
(conclusions unchanged); 27 pages, 9 figure
String-inspired cosmology
I discuss cosmological models either derived from, or inspired by, string
theory or M-theory. In particular I discuss solutions in the low-energy
effective theory and the role of the dilaton, moduli and antisymmetric form
fields in the dimensionally reduced effective action. The pre big bang model is
an attempt to use cosmological solutions to make observational predictions. I
then discuss the effective theory of gravity found in recent brane-world models
where we live on a 3-brane embedded in a five-dimensional spacetime and how the
study of cosmological perturbations may enable us to test these ideas.Comment: 15 pages, 5 figures, latex with iopart, invited talk at `The Early
Universe and Cosmological Observations: a Critical Review', Cape Town, July
200
Lorentz-violation and cosmological perturbations: a toy brane-world model
We study possible effects of Lorentz-violation on the generation of
cosmological perturbations at inflation by introducing a simple inflating
five-dimensional brane-world setup with violation of four-dimensional
Lorentz-invariance at an energy scale . We consider massless scalar field,
meant to mimic perturbations of inflaton and/or gravitational field, in this
background. At three-momenta below , there exists a zero mode localized on
the brane, whose behaviour coincides with that in four-dimensional theory. On
the contrary, at three-momenta above , the localized mode is absent and
physics is entirely five-dimensional. As three-momenta get redshifted, more
modes get localized on the brane, the phenomenon analogous to ``mode
generation''. We find that for , where is the inflationary Hubble
scale, the spectrum of perturbations coincides with that in four-dimensional
theory. For and time-dependent bulk parameters, the spectrum deviates,
possibly strongly, from the flat spectrum even for pure de Sitter inflation.Comment: 5 figures, iopart, minor changes, appendix adde
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