155 research outputs found
constant-roll inflation
The previously introduced class of two-parametric phenomenological
inflationary models in General Relativity in which the slow-roll assumption is
replaced by the more general, constant-roll condition is generalized to the
case of gravity. A simple constant-roll condition is defined in the
original Jordan frame, and exact expressions for a scalaron potential in the
Einstein frame, for a function (in the parametric form) and for
inflationary dynamics are obtained. The region of the model parameters
permitted by the latest observational constraints on the scalar spectral index
and the tensor-to-scalar ratio of primordial metric perturbations generated
during inflation is determined.Comment: 8 pages, 3 figures; added Fig. 2 and Appendix, matches published
versio
Constant-roll inflation: confrontation with recent observational data
The previously proposed class of phenomenological inflationary models in
which the assumption of inflaton slow-roll is replaced by the more general,
constant-roll condition is compared with the most recent cosmological
observational data, mainly the Planck ones. Models in this two-parametric class
which remain viable appear to be close to the slow-roll ones, and their
inflaton potentials are close to (but still different from) that of the natural
inflation model. Permitted regions for the two model parameters are presented.Comment: 4 pages, 1 figure; published versio
Correlation Functions in Stochastic Inflation
Combining the stochastic and formalisms, we derive non
perturbative analytical expressions for all correlation functions of scalar
perturbations in single-field, slow-roll inflation. The standard, classical
formulas are recovered as saddle-point limits of the full results. This yields
a classicality criterion that shows that stochastic effects are small only if
the potential is sub-Planckian and not too flat. The saddle-point approximation
also provides an expansion scheme for calculating stochastic corrections to
observable quantities perturbatively in this regime. In the opposite regime, we
show that a strong suppression in the power spectrum is generically obtained,
and comment on the physical implications of this effect.Comment: 20 pages plus appendix, 4 figures, published in EPJC, typo corrected
in Eq. (3.37
Stochastic dark energy from inflationary quantum fluctuations
We study the quantum backreaction from inflationary fluctuations of a very
light, non-minimally coupled spectator scalar and show that it is a viable
candiate for dark energy. The problem is solved by suitably adapting the
formalism of stochastic inflation. This allows us to self-consistently account
for the backreaction on the background expansion rate of the Universe where its
effects are large. This framework is equivalent to that of semiclassical
gravity in which matter vacuum fluctuations are included at the one loop level,
but purely quantum gravitational fluctuations are neglected. Our results show
that dark energy in our model can be characterized by a distinct effective
equation of state parameter (as a function of redshift) which allows for
testing of the model at the level of the background.Comment: 32 pages, 5 figures; published version, significant change
What do WMAP and SDSS really tell about inflation?
We derive new constraints on the Hubble function H(phi) and subsequently on
the inflationary potential V(phi) from WMAP 3-year data combined with the Sloan
Luminous Red Galaxy survey (SDSS-LRG), using a new methodology which appears to
be more generic, conservative and model-independent than in most of the recent
literature, since it depends neither on the slow-roll approximation, nor on any
extrapolation scheme for the potential beyond the observable e-fold range, nor
on additional assumptions about initial conditions for the inflaton velocity.
This last feature represents the main improvement of this work, and is made
possible by the reconstruction of H(phi) prior to V(phi). Our results only rely
on the assumption that within the observable range, corresponding to ~ 10
e-folds, inflation is not interrupted and the function H(phi) is smooth enough
for being Taylor-expanded at order one, two or three. We conclude that the
variety of potentials allowed by the data is still large. However, it is clear
that the first two slow-roll parameters are really small while the validity of
the slow-roll expansion beyond them is not established.Comment: 5 pages, 3 figures. Numerical module available at
http://wwwlapp.in2p3.fr/~valkenbu/inflationH/ . References added, discussion
expande
Is cosmic acceleration slowing down?
We investigate the course of cosmic expansion in its `recent past' using the
Constitution SN Ia sample (which includes CfA data at low redshifts), jointly
with signatures of baryon acoustic oscillations (BAO) in the galaxy
distribution and fluctuations in the cosmic microwave background (CMB). Earlier
SN Ia data sets could not address this issue because of a paucity of data at
low redshifts. Allowing the equation of state of dark energy (DE) to vary, we
find that a coasting model of the universe (q_0=0) fits the data about as well
as LCDM. This effect, which is most clearly seen using the recently introduced
`Om' diagnostic, corresponds to an increase of Om(z) and q(z) at redshifts z
\lleq 0.3. In geometrical terms, this suggests that cosmic acceleration may
have already peaked and that we are currently witnessing its slowing down. The
case for evolving DE strengthens if a subsample of the Constitution set
consisting of SNLS+ESSENCE+CfA SN Ia data is analysed in combination with
BAO+CMB using the same statistical methods. The effect we observe could
correspond to DE decaying into dark matter (or something else). A toy model
which mimics this process agrees well with the combined SN Ia+BAO+CMB data.Comment: 6 pages, 5 figures, presentation expanded, results for a new
subsample of the Constitution set are added, new BAO data are accounted for,
main results unchange
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