119 research outputs found
Constraining non standard recombination: A worked example
We fit the BOOMERANG, MAXIMA and COBE/DMR measurements of the cosmic
microwave background anisotropy in spatially flat cosmological models where
departures from standard recombination of the primeval plasma are parametrized
through a change in the fine structure constant compared to its
present value. In addition to we vary the baryon and dark matter
densities, the spectral index of scalar fluctuations, and the Hubble constant.
Within the class of models considered, the lack of a prominent second acoustic
peak in the measured spectrum can be accomodated either by a relatively large
baryon density, by a tilt towards the red in the spectrum of density
fluctuations, or by a delay in the time at which neutral hydrogen formed. The
ratio between the second and first peak decreases by around 25% either if the
baryon density is increased or the spectral index decreased
by a comparable amount, or if neutral hydrogen formed at a redshift about
15% smaller than its standard value. We find that the present data is best
fitted by a delay in recombination, with a lower baryon density than the best
fit if recombination is standard. Our best fit model has ,
, , and . Compatible with
present data at 95% confidence level ,
, and .Comment: 9 pages, 6 figs. Version accepted for publication in Phys.Rev.
Variation of the fine-structure constant: an update of statistical analyses with recent data
We analyze the consistency of different astronomical data of the variation in
the fine-structure constant obtained with KECK and VLT. We tested the
consistency using the Student test and confidence intervals. We splited the
data sets in to smaller intervals and grouped them acording to redshift and
angular position. Another statistical analysis is proposed that considers
phenomenological models for the variation in \alpha. Results show consistency
for the reduced intervals for each pair of data sets and suggests that the
variation in \alpha is significant at higher redshifts. Even though the dipole
model seems to be the most accurate phenomenological model, the statistical
analyses indicate that the variation in \alpha might be depending on both
redshift and angular position.Comment: 13 pages, 6 figures, Astronomy & Astrophysics, Accepted 25 June, 201
Primordial gravitational waves and the collapse of the wave function
"The self-induced collapse hypothesis" was introduced by D. Sudarsky and
collaborators to explain the origin of cosmic structure from a perfect
isotropic and homogeneous universe during the inflationary regime. In this
paper, we calculate the power spectrum for the tensor modes, within the
semiclassical gravity approximation, with the additional hypothesis of a
generic self-induced collapse of the inflaton's wave function; we also compute
an estimate for the tensor-to-scalar ratio. Based on this calculation, we show
that the considered proposal exhibits a strong suppression of the tensor modes
amplitude; nevertheless, the corresponding amplitude is still consistent with
the joint BICEP/KECK and Planck Collaboration's limit on the tensor-to-scalar
ratio.Comment: 18 pages, 2 figures. Replaced to match published versio
Quasi-matter bounce and inflation in the light of the CSL model
The Continuous Spontaneous Localization (CSL) model has been proposed as a
possible solution to the quantum measurement problem by modifying the
Schr\"{o}dinger equation. In this work, we apply the CSL model to two
cosmological models of the early Universe: the matter bounce scenario and slow
roll inflation. In particular, we focus on the generation of the classical
primordial inhomogeneities and anisotropies that arise from the dynamical
evolution, provided by the CSL mechanism, of the quantum state associated to
the quantum fields. In each case, we obtained a prediction for the shape and
the parameters characterizing the primordial spectra (scalar and tensor), i.e.
the amplitude, the spectral index and the tensor-to-scalar ratio. We found that
there exist CSL parameter values, allowed by other non-cosmological
experiments, for which our predictions for the angular power spectrum of the
CMB temperature anisotropy are consistent with the best fit canonical model to
the latest data released by the Planck Collaboration.Comment: 27 pages, including 6 figures, 2 tables and one Appendix. Final
version. Accepted in EPJ
Inflation including collapse of the wave function: The quasi-de Sitter case
The precise physical mechanism describing the emergence of the seeds of
cosmic structure from a perfect isotropic and homogeneous universe has not been
fully explained by the standard version of inflationary models. To handle this
shortcoming, D. Sudarsky and collaborators have developed a proposal: the
self-induced collapse hypothesis. In this scheme, the objective collapse of the
inflaton wave function is responsible for the emergence of inhomogeneity and
anisotropy at all scales. In previous papers, the proposal was developed with
an almost exact de Sitter space-time approximation for the background that led
to a perfect scale-invariant power spectrum. In the present article, we
consider a full quasi-de Sitter expansion and calculate the primordial power
spectrum for three different choices of the self-induced collapse. The
consideration of a quasi-de Sitter background allow us to distinguish
departures from an exact scale-invariant power spectrum that are due to the
inclusion of the collapse hypothesis. These deviations are also different from
the prediction of standard inflationary models with running spectral index.
Comparison with the primordial power spectrum and the CMB temperature
fluctuation spectrum preferred by the latest observational data is also
discussed. From the analysis performed in this work, it follows that most of
the collapse schemes analysed in this paper are viable candidates to explain
present observations of the CMB fluctuation spectrum.Comment: 24 pages, 12 figures. Replaced to match published versio
Supernovae, CMB, and Gravitational Leakage into Extra Dimensions
We discuss observational constraints coming from CMB and type Ia supernovae,
for the model of accelerated universe produced by gravitational leakage into
extra dimensions. Our fits indicate that the model is currently in agreement
with the data. We also give the equations governing the evolution of
cosmological perturbations. Future observations will be able to severely
constrain the model.Comment: 20 pages, 6 figures, typos corrected and minor changes before
publicatio
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