213 research outputs found
Constraints on Chaplygin quartessence from the CLASS gravitational lens statistics and supernova data
The nature of the dark components (dark matter and dark energy) that dominate
the current cosmic evolution is a completely open question at present. In
reality, we do not even know if they really constitute two separated
substances. In this paper we use the recent Cosmic All Sky Survey (CLASS)
lensing sample to test the predictions of one of the candidates for a unified
dark matter/energy scenario, the so-called generalized Chaplygin gas (Cg) which
is parametrized by an equation of state where
and are arbitrary constants. We show that, although the model is in
good agreement with this radio source gravitational lensing sample, the limits
obtained from CLASS statistics are only marginally compatible with the ones
obtained from other cosmological tests. We also investigate the constraints on
the free parameters of the model from a joint analysis between CLASS and
supernova data.Comment: 7 pages, 3 figures, to appear in Astronomy & Astrophysic
Supersymmetric Leptogenesis
We study leptogenesis in the supersymmetric standard model plus the seesaw.
We identify important qualitative differences that characterize supersymmetric
leptogenesis with respect to the non-supersymmetric case. The lepton number
asymmetries in fermions and scalars do not equilibrate, and are related via a
non-vanishing gaugino chemical potential. Due to the presence of new anomalous
symmetries, electroweak sphalerons couple to winos and higgsinos, and QCD
sphalerons couple to gluinos, thus modifying the corresponding chemical
equilibrium conditions. A new constraint on particles chemical potentials
corresponding to an exactly conserved -charge, that also involves the number
density asymmetry of the heavy sneutrinos, appears. These new ingredients
determine the matrices that mix up the density asymmetries of the
lepton flavours and of the heavy sneutrinos. We explain why in all temperature
ranges the particle thermodynamic system is characterized by the same number of
independent quantities. Numerical differences with respect to usual treatment
remain at the level.Comment: 30 pages, 2 figures. Typos corrected, one reference added. Version
published in JCA
Transition Redshift: New Kinematic Constraints from Supernovae
The transition redshift (deceleration/acceleration) is discussed by expanding
the deceleration parameter to first order around its present value. A detailed
study is carried out by considering two different parameterizations: and , and the associated free parameters () are constrained by 3 different supernova samples. The previous analysis
by Riess {\it{et al.}} [ApJ 607, 665, 2004] using the first expansion is
slightly improved and confirmed in light of their recent data ({\emph{Gold}}07
sample). However, by fitting the model with the Supernova Legacy Survey (SNLS)
type Ia sample we find that the best fit to the redshift transition is instead of as derived by the High-z Supernovae Search
(HZSNS) team. This result based in the SNLS sample is also in good agreement
with the Davis {\it{et al.}} sample, ().
Such results are in line with some independent analyzes and accommodates more
easily the concordance flat model (CDM). For both parameterizations,
the three SNe type Ia samples considered favor recent acceleration and past
deceleration with a high degree of statistical confidence level. All the
kinematic results presented here depend neither on the validity of general
relativity nor the matter-energy contents of the Universe.Comment: 19 pages, 15 figures, 1 table, revised version accepted for
publication in MNRA
CMBR Constraint on a Modified Chaplygin Gas Model
In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter , but allows it in the range .Comment: 4 pages, 3 figure
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Laboratory and field evaluation of acetic acid-based lures for male Asian citrus psyllid, Diaphorina citri.
The Asian citrus psyllid (ACP) is a vector of a pathogen associated with greening and thus a major problem in citriculture worldwide. Lures are much needed for improving ACP trapping systems for monitoring populations and surveillance. Previously, we have identified acetic acid as a putative sex pheromone and measured formic acid- and propionic acid-elicited robust electroantennographic responses. We have now thoroughly examined in indoor behavioral assays (4-way olfactometer) and field tests the feasibility of these three semiochemicals as potential lures for trapping ACP. Formic acid, acetic acid, and propionic acid at appropriate doses are male-specific attractants and suitable lures for ACP traps, but they do not act synergistically. An acetic acid-based homemade lure, prepared by impregnating the attractant in a polymer, was active for a day. A newly developed slow-release formulation had equal performance but lasted longer, thus leading to an important improvement in ACP trap capture at low population densities
SO(1,1) dark energy model and the universe transition
We suggest a scalar model of dark energy with the SO(1,1) symmetry. The model
may be reformulated in terms of a real scalar field and the scale factor
so that the Lagrangian may be decomposed as that of the real quintessence
model plus the negative coupling energy term of to . The existence of
the coupling term leads to a wider range of and overcomes the
problem of negative kinetic energy in the phantom universe model. We propose a
power-law expansion model of univese with time-dependent power, which can
describe the phantom universe and the universe transition from ordinary
acceleration to super acceleration.Comment: 12 pages. submitted to CQ
Dissipative Future Universe without Big Rip
The present study deals with dissipative future universe without big rip in
context of Eckart formalism. The generalized chaplygin gas, characterized by
equation of state , has been considered as
a model for dark energy due to its dark-energy-like evolution at late time. It
is demonstrated that, if the cosmic dark energy behaves like a fluid with
equation of state ; , as well as chaplygin gas
simultaneously then the big rip problem does not arises and the scale factor is
found to be regular for all time.Comment: 6 pages, 2 figures, To appear in Int. J. Theor. Phy
High-energy neutrino conversion and the lepton asymmetry in the universe
We study matter effects on oscillations of high-energy neutrinos in the
Universe. Substantial effect can be produced by scattering of the neutrinos
from cosmological sources (z\gta 1) on the relic neutrino background,
provided that the latter has large CP-asymmetry: \eta\equiv
(n_\nu-n_{\bar{\nu}})/n_\gamma\gta 1, where , and
are the concentrations of neutrinos, antineutrinos and photons. We
consider in details the dynamics of conversion in the expanding neutrino
background. Applications are given to the diffuse fluxes of neutrinos from
GRBs, AGN, and the decay of super-heavy relics. We find that the vacuum
oscillation probability can be modified by and in extreme cases
allowed by present bounds on the effect can reach .
Signatures of matter effects would consist (i) for both active-active and
active-sterile conversion, in a deviation of the numbers of events produced in
a detector by neutrinos of different flavours,
, and of their ratios from the values given by
vacuum oscillations; such deviations can reach , (ii) for
active-sterile conversion, in a characteristic energy dependence of the ratios
. Searches for these matter
effects will probe large CP and lepton asymmetries in the universe.Comment: 32 pages, RevTeX, 16 figures. Substantial changes in the treatment of
conversion effects in the relic neutrino background and of active-active
oscillations of high-energy neutrinos. Figures and references added;
conclusions partially modifie
Curvaton Dynamics in Brane-worlds
We study the curvaton dynamics in brane-world cosmologies. Assuming that the
inflaton field survives without decay after the end of inflation, we apply the
curvaton reheating mechanism to Randall-Sundrum and to its curvature
corrections: Gauss-Bonnet, induced gravity and combined Gauss-Bonnet and
induced gravity cosmological models. In the case of chaotic inflation and
requiring suppression of possible short-wavelength generated gravitational
waves, we constraint the parameters of a successful curvaton brane-world
cosmological model. If density perturbations are also generated by the curvaton
field then, the fundamental five-dimensional mass could be much lower than the
Planck massComment: 47 pages, 1 figure, references added, to be published in JCA
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