335 research outputs found
Is nonperturbative inflatino production during preheating a real threat to cosmology?
We discuss toy models where supersymmetry is broken due to non-vanishing
time-varying vacuum expectation value of the inflaton field during preheating.
We discuss the production of inflatino the superpartner of inflaton due to
vacuum fluctuations and then we argue that they do not survive until
nucleosynthesis and decay along with the inflaton to produce a thermal bath
after preheating. Thus the only relevant remnant is the helicity \pm 3/2
gravitinos which can genuinely cause problem to nucleosynthesis.Comment: 10 pages, Updates to match the accepted version in Phys. Rev.
The Formation of Cosmic Structures in a Light Gravitino Dominated Universe
We analyse the formation of cosmic structures in models where the dark matter
is dominated by light gravitinos with mass of eV -- 1 keV, as predicted
by gauge-mediated supersymmetry (SUSY) breaking models. After evaluating the
number of degrees of freedom at the gravitinos decoupling (), we compute
the transfer function for matter fluctuations and show that gravitinos behave
like warm dark matter (WDM) with free-streaming scale comparable to the galaxy
mass scale. We consider different low-density variants of the WDM model, both
with and without cosmological constant, and compare the predictions on the
abundances of neutral hydrogen within high-redshift damped Ly-- systems
and on the number density of local galaxy clusters with the corresponding
observational constraints. We find that none of the models satisfies both
constraints at the same time, unless a rather small value (\mincir
0.4) and a rather large Hubble parameter (\magcir 0.9) is assumed.
Furthermore, in a model with warm + hot dark matter, with hot component
provided by massive neutrinos, the strong suppression of fluctuation on scales
of \sim 1\hm precludes the formation of high-redshift objects, when the
low-- cluster abundance is required. We conclude that all different variants
of a light gravitino DM dominated model show strong difficulties for what
concerns cosmic structure formation.
This gives a severe cosmological constraint on the gauge-mediated SUSY
breaking scheme.Comment: 28 pages,Latex, submitted for publication to Phys.Rev.
Supergravity Inflation Free from Harmful Relics
We present a realistic supergravity inflation model which is free from the
overproduction of potentially dangerous relics in cosmology, namely moduli and
gravitinos which can lead to the inconsistencies with the predictions of baryon
asymmetry and nucleosynthesis. The radiative correction turns out to play a
crucial role in our analysis which raises the mass of supersymmetry breaking
field to intermediate scale. We pay a particular attention to the non-thermal
production of gravitinos using the non-minimal Kahler potential we obtained
from loop correction. This non-thermal gravitino production however is
diminished because of the relatively small scale of inflaton mass and small
amplitudes of hidden sector fields.Comment: 10 pages, revtex, 1 eps figure, references added, conclusion section
expande
On the exact gravitational lens equation in spherically symmetric and static spacetimes
Lensing in a spherically symmetric and static spacetime is considered, based
on the lightlike geodesic equation without approximations. After fixing two
radius values r_O and r_S, lensing for an observation event somewhere at r_O
and static light sources distributed at r_S is coded in a lens equation that is
explicitly given in terms of integrals over the metric coefficients. The lens
equation relates two angle variables and can be easily plotted if the metric
coefficients have been specified; this allows to visualize in a convenient way
all relevant lensing properties, giving image positions, apparent brightnesses,
image distortions, etc. Two examples are treated: Lensing by a
Barriola-Vilenkin monopole and lensing by an Ellis wormhole.Comment: REVTEX, 11 pages, 12 eps-figures, figures partly improved, minor
revision
Energy conditions, traversable wormholes and dust shells
Firstly, we review the pointwise and averaged energy conditions, the quantum
inequality and the notion of the ``volume integral quantifier'', which provides
a measure of the ``total amount'' of energy condition violating matter.
Secondly, we present a specific metric of a spherically symmetric traversable
wormhole in the presence of a generic cosmological constant, verifying that the
null and the averaged null energy conditions are violated, as was to be
expected. Thirdly, a pressureless dust shell is constructed around the interior
wormhole spacetime by matching the latter geometry to a unique vacuum exterior
solution. In order to further minimize the usage of exotic matter, we then find
regions where the surface energy density is positive, thereby satisfying all of
the energy conditions at the junction surface. An equation governing the
behavior of the radial pressure across the junction surface is also deduced.
Lastly, taking advantage of the construction, specific dimensions of the
wormhole, namely, the throat radius and the junction interface radius, and
estimates of the total traversal time and maximum velocity of an observer
journeying through the wormhole, are also found by imposing the traversability
conditions.Comment: 11 pages, 3 figures, Revtex
Double Inflation in Supergravity and the Large Scale Structure
The cosmological implication of a double inflation model with hybrid + new
inflations in supergravity is studied. The hybrid inflation drives an inflaton
for new inflation close to the origin through supergravity effects and new
inflation naturally occurs. If the total e-fold number of new inflation is
smaller than , both inflations produce cosmologically relevant density
fluctuations. Both cluster abundances and galaxy distributions provide strong
constraints on the parameters in the double inflation model assuming
standard cold dark matter scenario. The future satellite
experiments to measure the angular power spectrum of the cosmic microwave
background will make a precise determination of the model parameters possible.Comment: 19 pages (RevTeX file
Inflationary Cosmology with Five Dimensional SO(10)
We discuss inflationary cosmology in a five dimensional SO(10) model
compactified on , which yields below the compactification scale. The gauge
symmetry is preserved on one of the fixed points, while
``flipped'' is on the other fixed point. Inflation is
associated with breaking, and is implemented through -term scalar
potentials on the two fixed points. A brane-localized Einstein-Hilbert term
allows both branes to have positive tensions during inflation. The scale of
breaking is fixed from measurements to be around
GeV, and the scalar spectral index . The inflaton field
decays into right-handed neutrinos whose subsequent out of equilibrium decay
yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in
PR
Optimal designs for rational function regression
We consider optimal non-sequential designs for a large class of (linear and
nonlinear) regression models involving polynomials and rational functions with
heteroscedastic noise also given by a polynomial or rational weight function.
The proposed method treats D-, E-, A-, and -optimal designs in a
unified manner, and generates a polynomial whose zeros are the support points
of the optimal approximate design, generalizing a number of previously known
results of the same flavor. The method is based on a mathematical optimization
model that can incorporate various criteria of optimality and can be solved
efficiently by well established numerical optimization methods. In contrast to
previous optimization-based methods proposed for similar design problems, it
also has theoretical guarantee of its algorithmic efficiency; in fact, the
running times of all numerical examples considered in the paper are negligible.
The stability of the method is demonstrated in an example involving high degree
polynomials. After discussing linear models, applications for finding locally
optimal designs for nonlinear regression models involving rational functions
are presented, then extensions to robust regression designs, and trigonometric
regression are shown. As a corollary, an upper bound on the size of the support
set of the minimally-supported optimal designs is also found. The method is of
considerable practical importance, with the potential for instance to impact
design software development. Further study of the optimality conditions of the
main optimization model might also yield new theoretical insights.Comment: 25 pages. Previous version updated with more details in the theory
and additional example
First isolation and characterization of Leptospira interrogans serogroup Australis from swine in Brazil
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