19,186 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.
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
Magnetic ordering in GaAlAs:Mn double well structure
The magnetic order in the diluted magnetic semiconductor barrier of double
AlAs/GaAs: Mn quantum well structures is investigated by Monte Carlo
simulations. A confinement adapted RKKY mechanism is implemented for indirect
exchange between Mn ions mediated by holes. It is shown that, depending on the
barrier width and the hole concentration a ferromagnetic or a spin-glass order
can be established.Comment: 3 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
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