1,290 research outputs found
Constraints on inflation with LSS surveys: features in the primordial power spectrum
We analyse the efficiency of future large scale structure surveys to unveil
the presence of scale dependent features in the primordial spectrum --resulting
from cosmic inflation-- imprinted in the distribution of galaxies. Features may
appear as a consequence of non-trivial dynamics during cosmic inflation, in
which one or more background quantities experienced small but rapid deviations
from their characteristic slow-roll evolution. We consider two families of
features: localized features and oscillatory extended features. To characterise
them we employ various possible templates parametrising their scale dependence
and provide forecasts on the constraints on these parametrisations for LSST
like surveys. We perform a Fisher matrix analysis for three observables: cosmic
microwave background (CMB), galaxy clustering and weak lensing. We find that
the combined data set of these observables will be able to limit the presence
of features down to levels that are more restrictive than current constraints
coming from CMB observations only. In particular, we address the possibility of
gaining information on currently known deviations from scale invariance
inferred from CMB data, such as the feature appearing at the
multipole (which is the main contribution to the low- deficit) and a
potential feature appearing at .Comment: 37 pp., 5 Tabs., 10 Figs, v3: changed discussion around templates II,
III, added clarifications, comments and references. Matches JCAP versio
Thermodynamical aspects of running vacuum models
The thermal history of a large class of running vacuum models in which the
effective cosmological term is described by a truncated power series of the
Hubble rate, whose dominant term is , is discussed
in detail. Specifically, by assuming that the ultra-relativistic particles
produced by the vacuum decay emerge into space-time in such a way that its
energy density , the temperature evolution law and the
increasing entropy function are analytically calculated. For the whole class of
vacuum models explored here we findthat the primeval value of the comoving
radiation entropy density (associated to effectively massless particles) starts
from zero and evolves extremely fast until reaching a maximum near the end of
the vacuum decay phase, where it saturates. The late time conservation of the
radiation entropy during the adiabatic FRW phase also guarantees that the whole
class of running vacuum models predicts thesame correct value of the present
day entropy, (in natural units), independently of the
initial conditions. In addition, by assuming Gibbons-Hawking temperature as an
initial condition, we find that the ratio between the late time and primordial
vacuum energy densities is in agreement with naive estimates from quantum field
theory, namely, . Such results
are independent on the power and suggests that the observed Universe may
evolve smoothly between two extreme, unstable, nonsingular de Sitter phases.Comment: 15 pages in free style, 2 figures, to appear in European Phys.
Journal C.,(this work generalizes that of arXiv:1412.5196
Shapes and features of the primordial bispectrum
If time-dependent disruptions from slow-roll occur during inflation, the
correlation functions of the primordial curvature perturbation should have
scale-dependent features, a case which is marginally supported from the cosmic
microwave background (CMB) data. We offer a new approach to analyze the
appearance of such features in the primordial bispectrum that yields new
consistency relations and justifies the search of oscillating patterns
modulated by orthogonal and local templates. Under the assumption of sharp
features, we find that the cubic couplings of the curvature perturbation can be
expressed in terms of the bispectrum in two specific momentum configurations,
for example local and equilateral. This allows us to derive consistency
relations among different bispectrum shapes, which in principle could be tested
in future CMB surveys. Furthermore, based on the form of the consistency
relations, we construct new two-parameter templates for features that include
all the known shapes.Comment: (v1) 16 pages, 3 figures, 1 table; (v2) minor clarifications
including updated abstract, to appear in Journal of Cosmology and
Astroparticle Physic
On degenerate models of cosmic inflation
In this article we discuss the role of current and future CMB measurements in
pinning down the model of inflation responsible for the generation of
primordial curvature perturbations. By considering a parameterization of the
effective field theory of inflation with a modified dispersion relation arising
from heavy fields, we derive the dependence of cosmological observables on the
scale of heavy physics . Specifically, we show how the
non-linearity parameters are related to the phase velocity of
curvature perturbations at horizon exit, which is parameterized by
. Bicep2 and Planck findings are shown to be consistent with
a value . However, we find a
degeneracy in the parameter space of inflationary models that can only be
resolved with a detailed knowledge of the shape of the non-Gaussian bispectrum.Comment: 22pp., 1 fig; v2: added some clarifications and references, corrected
typos, matches published versio
Effective field theory of weakly coupled inflationary models
The application of Effective Field Theory (EFT) methods to inflation has
taken a central role in our current understanding of the very early universe.
The EFT perspective has been particularly useful in analyzing the
self-interactions determining the evolution of co-moving curvature
perturbations (Goldstone boson modes) and their influence on low-energy
observables. However, the standard EFT formalism, to lowest order in spacetime
differential operators, does not provide the most general parametrization of a
theory that remains weakly coupled throughout the entire low-energy regime.
Here we study the EFT formulation by including spacetime differential operators
implying a scale dependence of the Goldstone boson self-interactions and its
dispersion relation. These operators are shown to arise naturally from the
low-energy interaction of the Goldstone boson with heavy fields that have been
integrated out. We find that the EFT then stays weakly coupled all the way up
to the cutoff scale at which ultraviolet degrees of freedom become operative.
This opens up a regime of new physics where the dispersion relation is
dominated by a quadratic dependence on the momentum \omega ~ p^2. In addition,
provided that modes crossed the horizon within this energy range, the
prediction of inflationary observables - including non-Gaussian signatures -
are significantly affected by the new scales characterizing it.Comment: 36 pages, v2: references added, minor changes to match published
versio
Scale invariance of the primordial tensor power spectrum
Future cosmic microwave background polarization experiments will search for
evidence of primordial tensor modes at large angular scales, in the multipole
range Because in that range there is some mild evidence
of departures from scale invariance in the power spectrum of primordial
curvature perturbations, one may wonder about the possibility of similar
deviations appearing in the primordial power spectrum of tensor modes. Here we
address this issue and analyze the possible presence of features in the tensor
spectrum resulting from the dynamics of primordial fluctuations during
inflation. We derive a general, model independent, relation linking features in
the spectra of curvature and tensor perturbations. We conclude that even with
large deviations from scale invariance in the curvature power spectrum, the
tensor spectrum remains scale invariant for all observational purposes.Comment: 22 pages, 4 figures; v2: added references and clarifying comments;
v3: added reference and few more comments. Matches published versio
The Weyl tensor two-point function in de Sitter spacetime
We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.Comment: 9 pages, no figure
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