35 research outputs found
Momentum dependence of the bispectrum in two-field inflation
We examine the momentum dependence of the bispectrum of two-field
inflationary models within the long-wavelength formalism. We determine the
sources of scale dependence in the expression for the parameter of
non-Gaussianity fNL and study two types of variation of the momentum triangle:
changing its size and changing its shape. We introduce two spectral indices
that quantify the possible types of momentum dependence of the local type fNL
and illustrate our results with examples.Comment: 23 pages, 16 figures. v2: Final version. Minor textual change
The binned bispectrum estimator: template-based and non-parametric CMB non-Gaussianity searches
We describe the details of the binned bispectrum estimator as used for the
official 2013 and 2015 analyses of the temperature and polarization CMB maps
from the ESA Planck satellite. The defining aspect of this estimator is the
determination of a map bispectrum (3-point correlator) that has been binned in
harmonic space. For a parametric determination of the non-Gaussianity in the
map (the so-called fNL parameters), one takes the inner product of this binned
bispectrum with theoretically motivated templates. However, as a complementary
approach one can also smooth the binned bispectrum using a variable smoothing
scale in order to suppress noise and make coherent features stand out above the
noise. This allows one to look in a model-independent way for any statistically
significant bispectral signal. This approach is useful for characterizing the
bispectral shape of the galactic foreground emission, for which a theoretical
prediction of the bispectral anisotropy is lacking, and for detecting a
serendipitous primordial signal, for which a theoretical template has not yet
been put forth. Both the template-based and the non-parametric approaches are
described in this paper.Comment: Latex 42 pages with 10 figures and JCAP macros. v2: corrected small
mistake in section 5.3, changed colour scale of slice figures, other minor
changes and additions, matches published versio
Detecting Bispectral Acoustic Oscillations from Inflation Using a New Flexible Estimator
We present a new flexible estimator for comparing theoretical templates for
the predicted bispectrum of the CMB anisotropy to observations. This estimator,
based on binning in harmonic space, generalizes the optimal estimator of
Komatsu, Spergel, and Wandelt by allowing an adjustable weighting scheme for
masking possible foreground and other contaminants and detecting particular
noteworthy features in the bispectrum. The utility of this estimator is
illustrated by demonstrating how acoustic oscillations in the bispectrum and
other details of the bispectral shape could be detected in the future PLANCK
data provided that fNL is sufficiently large. The character and statistical
weight of the acoustic oscillations and the decay tail are described in detail.Comment: 15 pages, 9 jpeg and pdf figures, uses pdflatex and mn2e.cl
Isocurvature modes in the CMB bispectrum
We study the angular bispectrum of local type arising from the (possibly
correlated) combination of a primordial adiabatic mode with an isocurvature
one. Generically, this bispectrum can be decomposed into six elementary
bispectra. We estimate how precisely CMB data, including polarization, can
enable us to measure or constrain the six corresponding amplitudes, considering
separately the four types of isocurvature modes (CDM, baryon, neutrino density,
neutrino velocity). Finally, we discuss how the model-independent constraints
on the bispectrum can be combined to get constraints on the parameters of
multiple-field inflation models.Comment: 29 pages, 19 figures. v2: minor textual changes, matches published
versio
Constraining the bispectrum from bouncing cosmologies with Planck
Bouncing models of cosmology, as they arise e.g. in loop quantum cosmology,
can generate close-to-scale-invariant fluctuation spectra as observed in the
Cosmic Microwave Background (CMB). However, they are typically not Gaussian and
also generate a bispectrum. It was proposed that these models can help to
mitigate the large-scale anomalies of the CMB by considering large
non-Gaussianities on very large scales, which decay exponentially on
sub-horizon scales. It was therefore thought that this non-Gaussianity would
not be visible in observations, which can only probe sub-horizon scales. In
this letter we show that bouncing models with parameters such that they can
mitigate the large-scale anomalies of the CMB are excluded by the Planck data
with high significance of, depending on the specific model, or
standard deviations.Comment: 5 pages, 1 figur
Hunting for Isocurvature Modes in the CMB non-Gaussianities
We investigate new shapes of local primordial non-Gaussianities in the CMB.
Allowing for a primordial isocurvature mode along with the main adiabatic one,
the angular bispectrum is in general a superposition of six distinct shapes:
the usual adiabatic term, a purely isocurvature component and four additional
components that arise from correlations between the adiabatic and isocurvature
modes. We present a class of early Universe models in which various hierarchies
between these six components can be obtained, while satisfying the present
upper bound on the isocurvature fraction in the power spectrum. Remarkably,
even with this constraint, detectable non-Gaussianity could be produced by
isocurvature modes. We finally discuss the prospects of detecting these new
shapes with the Planck satellite.Comment: 9 pages, 2 figure
Gauge-invariant perturbations at second order in two-field inflation
We study the second-order gauge-invariant adiabatic and isocurvature
perturbations in terms of the scalar fields present during inflation, along
with the related fully non-linear space gradient of these quantities. We
discuss the relation with other perturbation quantities defined in the
literature. We also construct the exact cubic action of the second-order
perturbations (beyond any slow-roll or super-horizon approximations and
including tensor perturbations), both in the uniform energy density gauge and
the flat gauge in order to settle various gauge-related issues. We thus provide
the tool to calculate the exact non-Gaussianity beyond slow-roll and at any
scale.Comment: 28 pages, no figures. v2: Added a summary subsection 4.3 with further
discussion of the results. Generalized all super-horizon results of section 4
and appendix A to exact ones. Other minor textual changes and references
added. Conclusions unchanged. Matches published versio
Multiple-field inflation and the CMB
In this paper, we investigate some consequences of multiple-field inflation
for the cosmic microwave background radiation (CMB). We derive expressions for
the amplitudes, the spectral indices and the derivatives of the indices of the
CMB power spectrum in the context of a very general multiple-field theory of
slow-roll inflation, where the field metric can be non-trivial. Both scalar
(adiabatic, isocurvature and mixing) and tensor perturbations are treated and
the differences with single-field inflation are discussed. From these
expressions, several relations are derived that can be used to determine the
importance of multiple-field effects observationally from the CMB. We also
study the evolution of the total entropy perturbation during radiation and
matter domination and the influence of this on the isocurvature spectral
quantities.Comment: 24 pages. References added, some very minor textual changes, matches
version to be published in CQ