1,262 research outputs found
Supercurvaton
We discuss observational consequences of the curvaton scenario, which
naturally appears in the context of the simplest model of chaotic inflation in
supergravity. The non-gaussianity parameter f_NL in this scenario can take
values in the observationally interesting range from O(10) to O(100). These
values may be different in different parts of the universe. The regions where
f_NL is particularly large form a curvaton web resembling a net of thick domain
walls, strings, or global monopoles.Comment: 17 pages, 1 figure. Non-perturbative effects related to
non-gaussianity in the curvaton scenario are discussed, some references are
added. This is the version accepted in JCA
Self-consistent description of nuclear compressional modes
Isoscalar monopole and dipole compressional modes are computed for a variety
of closed-shell nuclei in a relativistic random-phase approximation to three
different parametrizations of the Walecka model with scalar self-interactions.
Particular emphasis is placed on the role of self-consistency which by itself,
and with little else, guarantees the decoupling of the spurious
isoscalar-dipole strength from the physical response and the conservation of
the vector current. A powerful new relation is introduced to quantify the
violation of the vector current in terms of various ground-state form-factors.
For the isoscalar-dipole mode two distinct regions are clearly identified: (i)
a high-energy component that is sensitive to the size of the nucleus and scales
with the compressibility of the model and (ii) a low-energy component that is
insensitivity to the nuclear compressibility. A fairly good description of both
compressional modes is obtained by using a ``soft'' parametrization having a
compression modulus of K=224 MeV.Comment: 28 pages and 10 figures; submitted to PR
Limits on the gravity wave contribution to microwave anisotropies
We present limits on the fraction of large angle microwave anisotropies which
could come from tensor perturbations. We use the COBE results as well as
smaller scale CMB observations, measurements of galaxy correlations, abundances
of galaxy clusters, and Lyman alpha absorption cloud statistics. Our aim is to
provide conservative limits on the tensor-to-scalar ratio for standard
inflationary models. For power-law inflation, for example, we find T/S<0.52 at
95% confidence, with a similar constraint for phi^p potentials. However, for
models with tensor amplitude unrelated to the scalar spectral index it is still
currently possible to have T/S>1.Comment: 23 pages, 7 figures, accepted for publication in Phys. Rev. D.
Calculations extended to blue spectral index, Fig. 6 added, discussion of
results expande
Isoscalar Giant Dipole Resonance and Nuclear Matter Incompressibility Coefficient
We present results of microscopic calculations of the strength function,
S(E), and alpha-particle excitation cross sections sigma(E) for the isoscalar
giant dipole resonance (ISGDR). An accurate and a general method to eliminate
the contributions of spurious state mixing is presented and used in the
calculations. Our results provide a resolution to the long standing problem
that the nuclear matter incompressibility coefficient, K, deduced from sigma(E)
data for the ISGDR is significantly smaller than that deduced from data for the
isoscalar giant monopole resonance (ISGMR).Comment: 4 pages using revtex 3.0, 3 postscript figures created by Mathematica
4.
The Importance of Slow-roll Corrections During Multi-field Inflation
We re-examine the importance of slow-roll corrections during the evolution of
cosmological perturbations in models of multi-field inflation. We find that in
many instances the presence of light degrees of freedom leads to situations in
which next to leading order slow-roll corrections become significant. Examples
where we expect such corrections to be crucial include models in which modes
exit the Hubble radius while the inflationary trajectory undergoes an abrupt
turn in field space, or during a phase transition. We illustrate this with two
examples -- hybrid inflation and double quadratic inflation. Utilizing both
analytic estimates and full numerical results, we find that corrections can be
as large as 20%. Our results have implications for many existing models in the
literature, as these corrections must be included to obtain accurate
observational predictions -- particularly given the level of accuracy expected
from CMB experiments such as PlanckComment: v1: 21 pages, 3 figures, 1 appendix. v2: clarifications to
{\S}{\S}2.1, 3.1 and 4, {\S}5.3 added, references added, results unchanged.
Matches published version in JCA
CMB polarization from secondary vector and tensor modes
We consider a novel contribution to the polarization of the Cosmic Microwave
Background induced by vector and tensor modes generated by the non-linear
evolution of primordial scalar perturbations. Our calculation is based on
relativistic second-order perturbation theory and allows to estimate the
effects of these secondary modes on the polarization angular power-spectra. We
show that a non-vanishing B-mode polarization unavoidably arises from pure
scalar initial perturbations, thus limiting our ability to detect the signature
of primordial gravitational waves generated during inflation. This secondary
effect dominates over that of primordial tensors for an inflationary
tensor-to-scalar ratio . The magnitude of the effect is smaller than
the contamination produced by the conversion of polarization of type E into
type B, by weak gravitational lensing. However the lensing signal can be
cleaned, making the secondary modes discussed here the actual background
limiting the detection of small amplitude primordial gravitational waves.Comment: 14 pages, 3 figures, minor changes matching the version to be
published in Phys. Rev.
Light Lambda-Lambda Hypernuclei and the Onset of Stability for Lambda-Xi Hypernuclei
New Faddeev-Yakubovsky calculations for light Lambda-Lambda hypernuclei are
presented in order to assess the self consistency of the Lambda-Lambda
hypernuclear binding-energy world data and the implied strength of the
Lambda-Lambda interaction, in the wake of recent experimental reports on
Lambda-Lambda-4H and Lambda-Lambda-6He. Using Gaussian soft-core simulations of
Nijmegen one-boson-exchange model interactions, the Nijmegen soft-core model
NSC97 simulations are found close to reproducing the recently reported binding
energy of Lambda-Lambda-6He, but not those of other species. For stranger
systems, Faddeev calculations of light Lambda-Xi hypernuclei, using a
simulation of the strongly attractive Lambda-Xi interactions due to the same
model, suggest that Lambda-Xi-6He marks the onset of nuclear stability for Xi
hyperons.Comment: 5 pages, 3 postscript figures; fig.2 replaced, minor changes,
accepted as Rapid Communication in PR
Archaeological Landscapes during the 10â8 ka Lake Stanley Lowstand on the AlpenaâAmberley Ridge, Lake Huron
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136243/1/gea21590.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136243/2/gea21590_am.pd
Home range and diving behaviour of Heaviside's dolphins monitored by satellite off the west coast of South Africa
Three Heavisideâs dolphins Cephalorhynchus heavisidii were fitted with satellite depth recorders off the west
coast of South Africa during FebruaryâApril 1997 and monitored for 51, 73 and 130 days, respectively. In total,
345 locations were received from the three animals, but only 27 from one male. Using -local convex hull and
minimum convex polygon methods, respectively, the home range for the remaining male was estimated at 1 520 and
2 347 km2, with corresponding core-area estimates (50% of locations) of 134 and 123 km2. For the female, the home
range estimates were 672 and 1 027 km2, and those for the core area were 71 and 230 km2. The femaleâs home range
was the smallest yet described for this species, and the animal was resighted nearly three years later within 13 km
of the tagging site. Binned dive data were received at 6-hourly intervals. From comparison of maximum dive depth
and time-at-depth data, we concluded that dives <4 m deep were associated with surfacing bouts. Dives to below
4 m occurred throughout 24 h but were shallower during the day and deepest either at dusk or at night. This pattern
was consistent with earlier descriptions of offshore movement during the day and may be related to the diel vertical
migration of its principal prey, shallow-water hake Merluccius capensis.http://www.tandfonline.com/loi/tams202015-12-30hb201
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