22,421 research outputs found
Gravitationally Induced Particle Production and its Impact on the WIMP Abundance
A large set of independent astronomical observations have provided a strong
evidence for nonbaryonic dark matter in the Universe. One of the most
investigated candidates is an unknown long-lived Weakly Interacting Massive
Particle (WIMP) which was in thermal equilibrium with the primeval plasma. Here
we investigate the WIMP abundance based on the relativistic kinetic treatment
for gravitationally induced particle production recently proposed in the
literature (Lima \& Baranov, Phys. Rev. D {\bf 90}, 043515, 2014). The new
evolution equation is deduced and solved both numerically and also through a
semi-analytical approach. The predictions of the WIMP observables are discussed
and compared with the ones obtained in the standard approach.Comment: 15 pages, 4 figures, discussion added in section 4. Accepted for
publication in Phys. Lett.
Gravitational Wave Emission and Mass Extraction from a Perturbed Schwarzschild Black Hole (continue)
A relativistic model for the emission of gravitational waves from an
initially unperturbed Schwarzschild black hole, or spherical collapsing
configuration, is completely integrated. The model consists basically of
gravitational perturbations of the Robinson-Trautman type on the Schwarzschild
spacetime. In our scheme of perturbation, gravitational waves may extract mass
from the collapsing configuration. Robinson-Trautmann perturbations also
include another mode of emission of mass, which we denote shell emission mode:
in the equatorial plane of the configuration, a timelike shell of
matter may be present, whose stress-energy tensor is modelled by neutrinos and
strings emitted radially on the shell; no gravitational waves are present in
this mode. The invariant characterization of gravitational wave perturbations
and of the gravitational wave zone is made through the analysis of the
structure of the curvature tensor and the use of the Peeling Theorem.Comment: 26 pages, LaTex, no figure
The specific entropy of elliptical galaxies: an explanation for profile-shape distance indicators?
Dynamical systems in equilibrium have a stationary entropy; we suggest that
elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may
have a unique specific entropy. This uniqueness, a priori unknown, should be
reflected in correlations between the parameters describing the mass (light)
distribution in galaxies. Following recent photometrical work (Caon et al.
1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to
describe the light profile of elliptical galaxies and an analytical
approximation to its three dimensional deprojection. The specific entropy is
calculated supposing that the galaxy behaves as a spherical, isotropic,
one-component system in hydrostatic equilibrium, obeying the ideal gas state
equations. We predict a relation between the 3 parameters of the Sersic,
defining a surface in the parameter space, an `Entropic Plane', by analogy with
the well-known Fundamental Plane. We have analysed elliptical galaxies in Coma
and ABCG 85 clusters and a group of galaxies (associated with NGC 4839). We
show that the galaxies in clusters follow closely a relation predicted by the
constant specific entropy hypothesis with a one-sigma dispersion of 9.5% around
the mean value of the specific entropy. Assuming that the specific entropy is
also the same for galaxies of different clusters, we are able to derive
relative distances between the studied clusters. If the errors are only due to
the determination of the specific entropy (about 10%), then the error in the
relative distance determination should be less than 20% for rich clusters. We
suggest that the unique specific entropy may provide a physical explanation for
the distance indicators based on the Sersic profile put forward by Young &
Currie (1994, 1995) and discussed by Binggeli & Jerjen (1998).Comment: Submitted to MNRAS (05/05/99), 15 pages, 10 figure
A tale of two Bethe ans\"atze
We revisit the construction of the eigenvectors of the single and double-row
transfer matrices associated with the Zamolodchikov-Fateev model, within the
algebraic Bethe ansatz method. The left and right eigenvectors are constructed
using two different methods: the fusion technique and Tarasov's construction. A
simple explicit relation between the eigenvectors from the two Bethe ans\"atze
is obtained. As a consequence, we obtain the Slavnov formula for the scalar
product between on-shell and off-shell Tarasov-Bethe vectors.Comment: 28 pages; v2: 30 pages, added proof of (4.40) and (5.39), minor
changes to match the published versio
On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer
A self-consistent calculation of the density of states and the spectral
density function is performed in a two-dimensional spin-polarized hole system
based on a multiple-scattering approximation. Using parameters corresponding to
GaMnAs thin layers, a wide range of Mn concentrations and hole densities have
been explored to understand the nature, localized or extended, of the
spin-polarized holes at the Fermi level for several values of the average
magnetization of the Mn ystem. We show that, for a certain interval of Mn and
hole densities, an increase on the magnetic order of the Mn ions come together
with a change of the nature of the states at the Fermi level. This fact
provides a delocalization of spin-polarized extended states anti-aligned to the
average Mn magnetization, and a higher spin-polarization of the hole gas. These
results are consistent with the occurrence of ferromagnetism with relatively
high transition temperatures observed in some thin film samples and
multilayered structures of this material.Comment: 3 page
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