31 research outputs found
The Void Abundance with Non-Gaussian Primordial Perturbations
We use a Press-Schechter-like calculation to study how the abundance of voids
changes in models with non-Gaussian initial conditions. While a positive
skewness increases the cluster abundance, a negative skewness does the same for
the void abundance. We determine the dependence of the void abundance on the
non-Gaussianity parameter fnl for the local-model bispectrum-which approximates
the bispectrum in some multi-field inflation models-and for the equilateral
bispectrum, which approximates the bispectrum in e.g. string-inspired DBI
models of inflation. We show that the void abundance in large-scale-structure
surveys currently being considered should probe values as small as fnl < 10 and
fnl^eq < 30, over distance scales ~10 Mpc.Comment: Submitted to JCA
Gravitational Lensing and f(R) theories in the Palatini approach
We investigate gravitational lensing in the Palatini approach to the f(R)
extended theories of gravity. Starting from an exact solution of the f(R) field
equations, which corresponds to the Schwarzschild-de Sitter metric and, on the
basis of recent studies on this metric, we focus on some lensing observables,
in order to evaluate the effects of the non linearity of the gravity
Lagrangian. We give estimates for some astrophysical events, and show that
these effects are tiny for galactic lenses, but become interesting for
extragalactic ones.Comment: 7 Pages, RevTex, 1 eps figure; references added; revised to match the
version accepted for publication in General Relativity and Gravitatio
UHECR as Decay Products of Heavy Relics? The Lifetime Problem
The essential features underlying the top-down scenarii for UHECR are
discussed, namely, the stability (or lifetime) imposed to the heavy objects
(particles) whatever they be: topological and non-topological solitons,
X-particles, cosmic defects, microscopic black-holes, fundamental strings. We
provide an unified formula for the quantum decay rate of all these objects as
well as the particle decays in the standard model. The key point in the
top-down scenarii is the necessity to adjust the lifetime of the heavy object
to the age of the universe. This ad-hoc requirement needs a very high
dimensional operator to govern its decay and/or an extremely small coupling
constant. The natural lifetimes of such heavy objects are, however, microscopic
times associated to the GUT energy scale (sim 10^{-28} sec. or shorter). It is
at this energy scale (by the end of inflation) where they could have been
abundantly formed in the early universe and it seems natural that they decayed
shortly after being formed.Comment: 11 pages, LaTex, no figures, updated versio
Calibration of Super-Kamiokande Using an Electron Linac
In order to calibrate the Super-Kamiokande experiment for solar neutrino
measurements, a linear accelerator (LINAC) for electrons was installed at the
detector. LINAC data were taken at various positions in the detector volume,
tracking the detector response in the variables relevant to solar neutrino
analysis. In particular, the absolute energy scale is now known with less than
1 percent uncertainty.Comment: 24 pages, 16 figures, Submitted to NIM
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SRS ECOLOGY ENVIRONMENTAL INFORMATION DOCUMENT -1997 UPDATE
The purpose of the SRS Ecology: Environmental Information Document is to provide a source of information on the ecology of the Savannah River Site