13,620 research outputs found
Gravitino Production Suppressed by Dynamics of Sgoldstino
In supersymmetric theories, the gravitino is abundantly produced in the early
Universe from thermal scattering, resulting in a strong upper bound on the
reheat temperature after inflation. We point out that the gravitino problem may
be absent or very mild due to the early dynamics of a supersymmetry breaking
field, i.e. a sgoldstino. In models of low scale mediation, the field value of
the sgoldstino determines the mediation scale and is in general different in
the early Universe from the present one. A large initial field value since the
era of the inflationary reheating suppresses the gravitino production
significantly. We investigate in detail the cosmological evolution of the
sgoldstino and show that the reheat temperature may be much higher than the
conventional upper bound, restoring the compatibility with thermal
leptogenesis.Comment: 23 pages, 3 figures; v2: discussions added and one figure updated,
matches version published in JHE
Useful residual hearing despite radiological findings suggestive of anacusis
A severe malformation of the inner ear, often referred to as severe labyrinthine dysplasia or common cavity deformity, consists of an absent or dilated cochlear basal coil, wide communication with the vestibule and a tapered internal acoustic meatus and can be associated with absent hearing. We discuss two children with severe labyrinthine dysplasia as shown by computed tomography (CT) scans and, in the first case, an absent VIIIth nerve bilaterally shown by magnetic resonance imaging (MRT). In 1995, both cases were precluded from cochlear implantation, on the basis of the absent VIIIth nerve (first case) and increased risk of CSF leak during operation (second case). However, audiometric results and vocalization patterns of both children suggested the presence of some residual hearing function, while recently reported specific surgical techniques have been found to be safe and effective in the cochlear implantation of the common cavity deformity. The management of such cases should be decided on the grounds of a full audiological assessment in conjunction with the radiological features, in the light of current surgical trends shown to be safe and effective
Gravitino or Axino Dark Matter with Reheat Temperature as high as GeV
A new scheme for lightest supersymmetric particle (LSP) dark matter is
introduced and studied in theories of TeV supersymmetry with a QCD axion, ,
and a high reheat temperature after inflation, . A large overproduction of
axinos () and gravitinos () from scattering at , and
from freeze-in at the TeV scale, is diluted by the late decay of a saxion
condensate that arises from inflation. The two lightest superpartners are
, with mass of order the TeV scale, and with mass
anywhere between the keV and TeV scales, depending on the mediation
scale of supersymmetry breaking. Dark matter contains both warm and cold
components: for LSP the warm component arises from , while for LSP the warm component arises
from . The free-streaming scale for the warm
component is predicted to be of order 1 Mpc (and independent of in
the case of LSP). can be as high as GeV, for any
value of , solving the gravitino problem. The PQ symmetry breaking
scale depends on and and can be anywhere in the range
GeV. Detailed predictions are made for the lifetime of
the neutralino LOSP decaying to and ,
which is in the range of m over much of parameter space. For an
axion misalignment angle of order unity, the axion contribution to dark matter
is sub-dominant, except when approaches GeV.Comment: 43 pages, 16 figure
Saxion Cosmology for Thermalized Gravitino Dark Matter
In all supersymmetric theories, gravitinos, with mass suppressed by the
Planck scale, are an obvious candidate for dark matter; but if gravitinos ever
reached thermal equilibrium, such dark matter is apparently either too abundant
or too hot, and is excluded. However, in theories with an axion, a saxion
condensate is generated during an early era of cosmological history and its
late decay dilutes dark matter. We show that such dilution allows previously
thermalized gravitinos to account for the observed dark matter over very wide
ranges of gravitino mass, keV < < TeV, axion decay constant,
GeV < < GeV, and saxion mass, 10 MeV < < 100 TeV.
Constraints on this parameter space are studied from BBN, supersymmetry
breaking, gravitino and axino production from freeze-in and saxion decay, and
from axion production from both misalignment and parametric resonance
mechanisms. Large allowed regions of remain, but differ
for DFSZ and KSVZ theories. Superpartner production at colliders may lead to
events with displaced vertices and kinks, and may contain saxions decaying to
or a pair of Standard Model fermions. Freeze-in
may lead to a sub-dominant warm component of gravitino dark matter, and saxion
decay to axions may lead to dark radiation.Comment: 30 pages, 4 figure
A Taskable Space Vehicle: Realizing Cost Savings by Combining Orbital and Suborbital Flight
The use of space gives the United States distinct advantages in any battlefield environment, but the high cost of space operations increasingly jeopardizes those advantages. Although the United States pioneered much of the current space technology, declining budgets for space research, development, and operations leave our legacy systems vulnerable to adversaries around the world. Other nations formerly incapable of space exploitation are quickly learning to counter US space technologies at surprisingly low costs. In order to reduce the expense of deploying and maintaining a robust space capability, the Department of Defense (DOD) must change the status quo in space operations or risk losing its dominance
Wave scattering by a partial flexible porous barrier in the presence of a step-type bottom topography
A semi-analytic model is presented for oblique wave scattering by a bottom-standing or surface-piercing flexible porous barrier in water of finite depth with a step-type bottom topography. The physical problem is solved using the methods of least-squares and multi-mode approximation associated with the modified mild-slope equation. Effects on the wave scattering due to bed profile, structural rigidity, compressive force, angle of incidence, barrier length, porosity, and height of the step are examined. The study reveals that under some special conditions, nearly zero/full reflection may occur in the case of wave scattering by a partial flexible porous barrier in the presence of an undulated bottom topography.
Further, the study predicts that the Bragg resonance may not occur in the case of wave scattering by a topography of sinusoidal profile. The present study provides insights to help understand how waves are transformed in a marine environment with/without flexible porous barriers in the presence of a bottom topography. The concept and methodology can be generalized to analyze problems of similar nature arising in ocean engineering.postprin
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