3,551 research outputs found
Acceleration field of a Universe modeled as a mixture of scalar and matter fields
A model of the Universe as a mixture of a scalar (inflaton or rolling tachyon
from the string theory) and a matter field (classical particles) is analyzed.
The particles are created at the expense of the gravitational energy through an
irreversible process whereas the scalar field is supposed to interact only with
itself and to be minimally coupled with the gravitational field. The
irreversible processes of particle creation are related to the non-equilibrium
pressure within the framework of the extended (causal or second-order)
thermodynamic theory. The scalar field (inflaton or tachyon) is described by an
exponential potential density added by a parameter which represents its
asymptotic value and can be interpreted as the vacuum energy. This model can
simulate three phases of the acceleration field of the Universe, namely,(a) an
inflationary epoch with a positive acceleration followed by a decrease of the
acceleration field towards zero, (b) a past decelerated period where the
acceleration field decreases to a maximum negative value followed by an
increase towards zero, and (c) a present accelerated epoch. For the energy
densities there exist also three distinct epochs which begin with a scalar
field dominated period followed by a matter field dominated epoch and coming
back to a scalar field dominated phase.Comment: 9 pages, 2 figures, to be published in General Relativity and
Gravitatio
Existence and concentration of ground state solutions for a critical nonlocal Schr\"odinger equation in
We study the following singularly perturbed nonlocal Schr\"{o}dinger equation
-\vr^2\Delta u +V(x)u =\vr^{\mu-2}\Big[\frac{1}{|x|^{\mu}}\ast F(u)\Big]f(u)
\quad \mbox{in} \quad \R^2, where is a continuous real function on
, is the primitive of , and \vr is a positive
parameter. Assuming that the nonlinearity has critical exponential
growth in the sense of Trudinger-Moser, we establish the existence and
concentration of solutions by variational methods.Comment: 3
Goldstone Gauginos
Models of supersymmetry with Dirac gauginos provide an attractive scenario
for physics beyond the standard model. The "supersoft" radiative corrections
and suppressed SUSY production at colliders provide for more natural theories
and an understanding of why no new states have been seen. Unfortunately, these
models are handicapped by a tachyon which is naturally present in existing
models of Dirac gauginos. We argue that this tachyon is absent, with the
phenomenological successes of the model preserved, if the right handed gaugino
is a (pseudo-)Goldstone field of a spontaneously broken anomalous flavor
symmetry.Comment: 5 pages, 1 figure. v2: minor changes to text, references added and
update
Models of Goldstone Gauginos
Models with Dirac gauginos provide appealing scenarios for physics beyond the
standard model. They have smaller radiative corrections to the Higgs mass, a
suppression of certain SUSY production processes, and ameliorated flavor
constraints. Unfortunately, they also generally have tachyons, the solutions to
which typically spoil these positive features. The recently proposed "Goldstone
Gaugino" mechanism provides a simple solution that eliminates these tachyonic
states. We provide details on this mechanism and explore models for its origin.
In particular, we find SUSY QCD models that realize this idea simply, and
discuss scenarios for unification.Comment: 33 pages, 4 figure
The Poker Face of Inelastic Dark Matter: Prospects at Upcoming Direct Detection Experiments
The XENON100 and CRESST experiments will directly test the inelastic dark
matter explanation for DAMA's 8.9? sigma anomaly. This article discusses how
predictions for direct detection experiments depend on uncertainties in
quenching factor measurements, the dark matter interaction with the Standard
Model and the halo velocity distribution. When these uncertainties are
accounted for, an order of magnitude variation is found in the number of
expected events at CRESST and XENON100.Comment: 5 pages, 3 figure
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