1,772 research outputs found
Three-form inflation and non-Gaussianity
We calculate the perturbed action, at second and third order, for a massive
three-form field minimally coupled to gravity, and use it to explore the
observational predictions of three-form inflation. One intriguing result is
that the value of the spectral index is nearly independent of the three-form
potential, being fixed solely by the number of e-folds of inflation, with
n_s=0.97 for the canonical number of 60. Considering the bispectrum, we employ
standard techniques to give explicit results for two models, one of which
produces a large non-Gaussianity. Finally, we confirm our results by employing
a duality relating the three-form theory to a non-canonical scalar field theory
and explicitly re-computing results in this dual picture.Comment: 23 pages, 6 figures. Typos corrected and addition of one appendix.
Accepted in JCA
Inflation in a two 3-form fields scenario
A setting constituted by 3-form fields, without any direct
interaction between them, minimally coupled to gravity, is introduced in this
paper as a framework to study the early evolution of the universe. We focus
particularly on the two 3-forms case. An inflationary scenario is found,
emerging from the coupling to gravity. More concretely, the fields coupled in
this manner exhibit a complex interaction, mediated by the time derivative of
the Hubble parameter. Our investigation is supported by means of a suitable
choice of potentials, employing numerical methods and analytical
approximations. In more detail, the oscillations on the small field limit
become correlated, and one field is intertwined with the other. In this type of
solution, a varying sound speed is present, together with the generation of
isocurvature perturbations. The mentioned features allow to consider an
interesting model, to test against observation. It is subsequently shown how
our results are consistent with current CMB data (viz.Planck and BICEP2).Comment: Version accepted in JCAP. 22 pages, 12 figures, new refs adde
A Review on the Cosmology of the de Sitter Horndeski Models
We review the most general scalar-tensor cosmological models with up to
second-order derivatives in the field equations that have a fixed spatially
flat de Sitter critical point independent of the material content or vacuum
energy. This subclass of the Horndeski Lagrangian is capable of dynamically
adjusting any value of the vacuum energy of the matter fields at the critical
point. We present the cosmological evolution of the linear models and the
non-linear models with shift symmetry. We come to the conclusion that the shift
symmetric non-linear models can deliver a viable background compatible with
current observations.Comment: 7 pages, 2 figures. Proceedings accepted for publication in
"Universe", Special Issue "Varying Constants and Fundamental Cosmology" for
the VARCOSMOFUN16 in Szczecin, Poland, 12-17 September, 201
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