36 research outputs found
Semi-Classical Isotropization of the Universe during a de Sitter phase
Semi-classical states for the Wheeler-DeWitt equation of a Bianchi type I
model in the presence of a scalar field are analyzed. It is outlined how this
scheme can effectively describe more general situations, where the curvature of
the Bianchi type IX model and a proper potential term for the scalar field are
present. The introduction of a cosmological constant term accounts for the
quasi-isotropization mechanism which bridges the proposed framework with a late
isotropic phase. This result makes the semi-classical Bianchi I model a
plausible scenario for the Universe pre-inflationary phase.Comment: 6 pages, accepted for publication in Phys. Rev.
Healing the cosmological constant problem during inflation through a unified quasi-quintessence matter field
We heal the cosmological constant problem by means of a \emph{cancellation
mechanism} that adopts a phase transition during which quantum fluctuations are
eliminated. To this purpose, we propose that a generalized scalar (dark) matter
field with a non-vanishing pressure term can remove the vacuum energy
contribution, if its corresponding thermodynamics is written in terms of a
\emph{quasi-quintessence} representation. In such a picture, pressure differs
from quintessence as it shows a zero kinetic contribution. Using this field, we
investigate a metastable transition phase, in which the universe naturally
passes through an inflationary phase. To reach this target, we single out a
double exponential potential, describing the metastable inflationary dynamics
by considering suitable boundaries and thermodynamic conditions. We analyze
stability investigating saddle, stable and unstable points and we thus predict
a chaotic inflation that mimics the Starobinsky exponential potential.
Consequently, the role of the proposed dark matter field is investigated
throughout the overall universe evolution. To do so, we provide a physical
explanation on unifying the dark sector with inflation by healing the
cosmological constant problem.Comment: 12 pages, 3 figures, 2 table
New measurements of from gamma-ray bursts
Context: Data from cosmic microwave background radiation (CMB), baryon
acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark
energy equation of state with . Measuring the evolution of
along the redshift is one of the most demanding challenges for observational
cosmology. Aims: We discuss the existence of a close relation for GRBs, named
Combo-relation, based on characteristic parameters of GRB phenomenology such as
the prompt intrinsic peak energy , the X-ray afterglow, the initial
luminosity of the shallow phase , the rest-frame duration of the
shallow phase, and the index of the late power-law decay . We use it
to measure and the evolution of the dark energy equation of state.
We also propose a new calibration method for the same relation, which reduces
the dependence on SNe Ia systematics. Methods: We have selected a sample of
GRBs with 1) a measured redshift ; 2) a determined intrinsic prompt peak
energy , and 3) a good coverage (0.3-10) keV afterglow light curves.
The fitting technique of the rest.frame (0.3-10) keV luminosity light curves
represents the core of the Combo-relation. We separate the early steep decay,
considered a part of the prompt emission, from the X-ray afterglow additional
component. Data with the largest positive residual, identified as flares, are
automatically eliminated until the p-value of the fit becomes greater than 0.3.
Results: We strongly minimize the dependency of the Combo-GRB calibration on
SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation,
which allows us to infer from GRBs alone
(1) for the CDM cosmological model, and , for the flat-Universe
variable equation of state case.Comment: 10 pages, 9 figures, 3 tables. Accepted for publication in A&A.
Truncated abstract tex
Neutrino oscillation in the -metric
We investigate neutrino oscillation in the field of an axially symmetric
space-time, employing the so-called -metric, in the context of general
relativity. Following the standard approach, we compute the phase shift
invoking the weak and strong field limits and small deformation. To do so, we
consider neutron stars, white dwarfs and supernovae as strong gravitational
regimes whereas the Solar System as weak field regime. We argue that the
inclusion of the quadrupole parameter leads to the modification of the
well-known results coming from the spherical solution due to the Schwarschild
space-time. Hence, we show that in the Solar System regime, considering the
Earth and Sun, there is a weak probability to detect deviations from the flat
case, differently from the case of neutron stars and white dwarfs in which this
probability is larger. Thus, we heuristically discuss some implications on
constraining the free parameters of the phase shift by means of astrophysical
neutrinos. A few consequences in cosmology and possible applications for future
space experiments are also discussed throughout the text.Comment: 2 figures, 3 tables, accepted for publication in EPJ