320 research outputs found
Space-time symmetry restoration in cosmological models with Kalb--Ramond and scalar fields
We study symmetry of space-time in presence of a minimally coupled scalar
field interacting with a Kalb--Ramond tensor fields in a homogeneous but
initially anisotropic universe. The analysis is performed for the two relevant
cases of a pure cosmological constant and a minimal quadratic, renormalizable,
interaction term. In both cases, due to expansion, a complete spatial symmetry
restoration is dynamically obtained.Comment: Latex, 7 pages, 3 eps figure
Detecting planets around stars in nearby galaxies
The only way to detect planets around stars at distances of several kpc is by
(photometric or astrometric) microlensing observations. In this paper, we show
that the capability of photometric microlensing extends to the detection of
signals caused by planets around stars in nearby galaxies (e.g. M31) and that
there is no other method that can achieve this. Due to the large crowding,
microlensing experiments towards M31 can only observe the high-magnification
part of a lensing light curve. Therefore, the dominating channel for
microlensing signals by planets is in distortions near the peak of
high-magnification events as discussed by Griest and Safizadeh. We calculate
the probability to detect planetary anomalies for microlensing experiments
towards M31 and find that jupiter-like planets around stars in M31 can be
detected. Though the characterization of the planet(s) involved in this signal
will be difficult, the absence of such signals can yield strong constraints on
the abundance of jupiter-like planets.Comment: 16 LaTex Pages, including 1 Postscript Figures, submitted to A&A;
title changed, one more author added, completely revised version: central
point is detecting planet in nearby galaxies and one more technique is taken
into consideratio
Distances in inhomogeneous quintessence cosmology
We investigate the properties of cosmological distances in locally
inhomogeneous universes with pressureless matter and dark energy
(quintessence), with constant equation of state. We give exact solutions for
angular diameter distances in theempty beam approximation. In this hypothesis,
the distance-redshift equation is derived fron the multiple lens-plane theory.
The case of a flat universe is considered with particular attention. We show
how this general scheme makes distances degenerate with respect to w_X and the
smoothness parameters, alpha, accounting for the homogeneously distributed
fraction of energy of the i-components. We analyse how this degeneracy
influences the critical redshift where the angular diameter distance takes its
maximum, and put in evidence future prospects for measuring the smoothness
parameter of the pressureless matter, alpha_M.Comment: 24 pages, 9 ps figure
Acoustic emission (AE) as a diagnostic tool in geophysics
Acoustic Emissions (AE) are effective for monitoring ground deformation and temporal variation of its porosity. AE are complementary to seismic information, related to the same area, though AE and earthquakes focus on observational evidence concerned with substantially different space- and time-scales. AE information is pertinent (i) either for geodynamically stable areas, where it probes the diurnal thermal and/or tidal deformation, (ii) or for seismic areas where it provides some as yet unexploited precursors, (iii) or for volcanic areas, where it appears capable of recognising precursors originated by some hot fluid that penetrates by diffusion into rock pores, from those associated with eventual plutonic magma intrusions, (iv) and also for monitoring periods of time during which a volcano is «inflated» by underground hot fluids compared to others during which it «deflates». Upon direct comparison between 6 data sets concerned with different physical settings, it seems to be possible (fig. 3 and table II] to distinguish a few significantly different behaviours associated either (i) with a mere compression (such as it occurs for Stromboli, Vesuvius, and a sample compressed in the laboratory), or (ii) with a slip strain, such as it typically occurs in association with faulting or with diurnal thermal rock deformation
Coupling parameters and the form of the potential via Noether symmetry
We explore the conditions for the existence of Noether symmetries in the
dynamics of FRW metric, non minimally coupled with a scalar field, in the most
general situation, and with nonzero spatial curvature. When such symmetries are
present we find general exact solution for the Einstein equations. We also show
that non Noether symmetries can be found.
Finally,we present an extension of the procedure to the Kantowski- Sachs
metric which is particularly interesting in the case of degenerate Lagrangian.Comment: 13 pages, no figure
Slott-Agape Project
SLOTT-AGAPE (Systematic Lensing Observation at Toppo Telescope - Andromeda
Gravitational Amplification Pixel Lensing Experiment) is a new collaboration
project among international partners from England, France, Germany, Italy and
Switzerland that intends to perform microlensing observation by using M31 as
target. The MACHOs search is made thanks to the pixel lensing technique.Comment: 4 pages, 2 figures, proceeding of XLIII Congresso della Societa'
Astronomica Italiana, Napoli, 4-8 Maggio, 199
Oscillating dark energy: a possible solution to the problem of eternal acceleration
We present a dark energy model with a double exponential potential for a
minimally coupled scalar field, which allows general exact integration of the
cosmological equations. The solution can perfectly emulate a -term
model at low-medium redshift, exhibits tracking behavior, and does not show
eternal acceleration.Comment: 15 pages, 7 figures included, to appear in Physical Review
Acoustic Emission (AE) as a diagnostic tool in geophysics
Acoustic Emissions (AE) are effective for monitoring ground deformation and temporal variation of its porosity. AE are complementary to seismic information, related to the same area, though AE and earthquakes focus on observational evidence concerned with substantially different space- and time-scales. AE information is pertinent (i) either for geodynamically stable areas, where it probes the diurnal thermal and/or tidal deformation, (ii) or for seismic areas where it provides some as yet unexploited precursors, (iii) or for volcanic areas, where it appears capable of recognising precursors originated by some hot fluid that penetrates by diffusion into rock pores, from those associated with eventual plutonic magma intrusions, (iv) and also for monitoring periods of time during which a volcano is «inflated» by underground hot fluids compared to others during which it «deflates». Upon direct comparison between 6 data sets concerned with different physical settings, it seems to be possible (fig. 3 and table II] to distinguish a few significantly different behaviours associated either (i) with a mere compression (such as it occurs for Stromboli, Vesuvius, and a sample compressed in the laboratory), or (ii) with a slip strain, such as it typically occurs in association with faulting or with diurnal thermal rock deformation
On Some Exponential Potentials for a Cosmological Scalar Field as Quintessence
We present general exact solutions for two classes of exponential potentials
in scalar field models for quintessence. The coupling is minimal and we
consider only dust and scalar field. To some extent, it is possible to
reproduce experimental results from supernovae.Comment: revised version. To appear Gen. Rel. Gra
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