10,190 research outputs found
Ground-based CCD astrometry with wide field imagers. IV. An improved Geometric Distortion Correction for the Blue prime-focus Camera at the LBT
High precision astrometry requires an accurate geometric distortion solution.
In this work, we present an average correction for the Blue Camera of the Large
Binocular Telescope which enables a relative astrometric precision of ~15 mas
for the B_Bessel and V_Bessel broad-band filters. The result of this effort is
used in two companion papers: the first to measure the absolute proper motion
of the open cluster M67 with respect to the background galaxies; the second to
decontaminate the color-magnitude diagram of M67 from field objects, enabling
the study of the end of its white dwarf cooling sequence. Many other
applications might find this distortion correction useful.Comment: 13 pages, 11 figures, 4 tables. accepted for publication on Astronomy
and Astrophysic
Thermodynamical properties of metric fluctuations during inflation
I study a thermodynamical approach to scalar metric perturbations during the
inflationary stage. In the power-law expanding universe here studied, I find a
negative heat capacity as a manifestation of superexponential growing for the
number of states in super Hubble scales. The power spectrum depends on the
Gibbons-Hawking and Hagedorn temperatures.Comment: 7 pages, no figures (accepted to publication in General Relativity
and Gravitation
Fresh inflation and decoherence of super Hubble fluctuations
I study a stochastic approach to the recently introduced fresh inflation
model for super Hubble scales. I find that the state loses its coherence at the
end of the fresh inflationary period as a consequence of the damping of the
interference function in the reduced density matrix. This fact should be a
consequence of a) the relative evolutions of both the scale factor and the
horizon and b) the additional thermal and dissipative effects. This implies a
relevant difference with respect to supercooled inflationary scenarios which
require a very rapid expansion of the scale factor to give the decoherence of
super Hubble fluctuations.Comment: version with minor changes. To appear in Phys. Rev.
Warm inflation and scalar perturbations of the metric
A second-order expansion for the quantum fluctuations of the matter field was
considered in the framework of the warm inflation scenario. The friction and
Hubble parameters were expended by means of a semiclassical approach. The
fluctuations of the Hubble parameter generates fluctuations of the metric.
These metric fluctuations produce an effective term of curvature. The power
spectrum for the metric fluctuations can be calculated on the infrared sector.Comment: 10 pages, no figures, to be published in General Rel. and Gravitatio
Astrometry and photometry with HST-WFC3. I. Geometric distortion corrections of F225W, F275W, F336W bands of the UVIS-channel
An accurate geometric distortion solution for the Hubble Space Telescope
UVIS-channel of Wide Field Camera 3 is the first step towards its use for high
precision astrometry. In this work we present an average correction that
enables a relative astrometric accuracy of ~1 mas (in each axis for well
exposed stars) in three broad-band ultraviolet filters (F225W, F275W, and
F336W). More data and a better understanding of the instrument are required to
constrain the solution to a higher level of accuracy.Comment: 20 pages, 7 figures (3 in low resolution), 3 tables. Accepted for
publication in PASP on October 16 200
Fresh inflation: a warm inflationary model from a zero temperature initial state
A two-components mixture fluid which complies with the gamma law is
considered in the framework of inflation with finite temperature. The model is
developed for a quartic scalar potential without symmetry breaking. The
radiation energy density is assumed to be zero when inflation starts and
remains below the GUT temperature during the inflationary stage. Furthermore,
provides the necessary number of e-folds and sufficient radiation energy
density to GUT baryogenesis can take place near the minimum energetic
configuration.Comment: 11 pages, no figures, to be published in Phys. Rev.
Geometric back-reaction in pre-inflation from relativistic quantum geometry
The pre-inflationary evolution of the universe describes the beginning of the
expansion from a static initial state, such that the Hubble parameter is
initially zero, but increases to an asymptotic constant value, in which it
could achieve a de Sitter (inflationary) expansion. The expansion is driven by
a background phantom field. The back-reaction effects at this moment should
describe vacuum geometrical excitations, which are studied with detail in this
work using Relativistic Quantum Geometry.Comment: improved versio
A confirmation of agreement of different approaches for scalar gauge-invariant metric perturbations during inflation
We revisit an extension of the well-known formalism for gauge-invariant
scalar metric fluctuations, to study the spectrums for both, the inflaton and
gauge invariant (scalar) metric fluctuations in the framework of a single field
inflationary model where the quasi-exponential expansion is driven by an
inflation which is minimally coupled to gravity. The proposal here examined is
valid also for fluctuations with large amplitude, but for cosmological scales,
where vector and tensor perturbations can be neglected and the fluid is
irrotacional.Comment: Version accepted in EPJC with new title. 11 pages, no figure
Charged and electromagnetic fields from relativistic quantum geometry
In the Relativistic Quantum Geometry (RQG) formalism recently introduced, was
explored the possibility that the variation of the tensor metric can be done in
a Weylian integrable manifold using a geometric displacement, from a Riemannian
to a Weylian integrable manifold, described by the dynamics of an auxiliary
geometrical scalar field , in order that the Einstein tensor (and the
Einstein equations) can be represented on a Weyl-like manifold. In this
framework we study jointly the dynamics of electromagnetic fields produced by
quantum complex vector fields, which describes charges without charges. We
demonstrate that complex fields act as a source of tetra-vector fields which
describe an extended Maxwell dynamics.Comment: improved versio
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