1,949 research outputs found
Gravity and non-gravity mediated couplings in multiple-field inflation
Mechanisms for the generation of primordial non-Gaussian metric fluctuations
in the context of multiple-field inflation are reviewed. As long as kinetic
terms remain canonical, it appears that nonlinear couplings inducing
non-gaussianities can be split into two types. The extension of the one-field
results to multiple degrees of freedom leads to gravity mediated couplings that
are ubiquitous but generally modest. Multiple-field inflation offers however
the possibility of generating non-gravity mediated coupling in isocurvature
directions that can eventually induce large non-Gaussianities in the metric
fluctuations. The robustness of the predictions of such models is eventually
examined in view of a case study derived from a high-energy physics
construction.Comment: 14 pages, 3 figures, invited review for CQG issue on non-linear
cosmolog
Scale dependence of in N-flation
Adopting the horizon-crossing approximation, we derive the spectral index of
in general N-flation model. Axion N-flation model is taken as a
typical model for generating a large which characterizes the size of
local form bispectrum. We find that its tilt is negligibly small
when all inflatons have the same potential, but a negative detectable
can be achieved in the axion N-flation with different decay
constants for different inflatons. The measurement of can be used
to support or falsify the axion N-flation in the near future.Comment: 15 pages, 2 figures; a subsection with detectable scale dependence of
f_NL added; more discussions added and version accepted for publication in
JCA
Scale-Dependent Non-Gaussianity as a Generalization of the Local Model
We generalize the local model of primordial non-Gaussianity by promoting the
parameter fNL to a general scale-dependent function fNL(k). We calculate the
resulting bispectrum and the effect on the bias of dark matter halos, and thus
the extent to which fNL(k) can be measured from the large-scale structure
observations. By calculating the principal components of fNL(k), we identify
scales where this form of non-Gaussianity is best constrained and estimate the
overlap with previously studied local and equilateral non-Gaussian models.Comment: Accepted to JCAP. 22 pages, 4 figure
Inhomogeneous non-Gaussianity
We propose a method to probe higher-order correlators of the primordial
density field through the inhomogeneity of local non-Gaussian parameters, such
as f_NL, measured within smaller patches of the sky. Correlators between
n-point functions measured in one patch of the sky and k-point functions
measured in another patch depend upon the (n+k)-point functions over the entire
sky. The inhomogeneity of non-Gaussian parameters may be a feasible way to
detect or constrain higher-order correlators in local models of
non-Gaussianity, as well as to distinguish between single and multiple-source
scenarios for generating the primordial density perturbation, and more
generally to probe the details of inflationary physics.Comment: 16 pages, 2 figures; v2: Minor changes and references added. Matches
the published versio
CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and \tau_{NL}) and a New Consistency Test of Single-Field Inflation
We outline the expected constraints on non-Gaussianity from the cosmic
microwave background (CMB) with current and future experiments, focusing on
both the third (f_{NL}) and fourth-order (g_{NL} and \tau_{NL}) amplitudes of
the local configuration or non-Gaussianity. The experimental focus is the
skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra
from weighted maps. In adition to a measurement of \tau_{NL} and g_{NL} with
WMAP 5-year data, our study provides the first forecasts for future constraints
on g_{NL}. We describe how these statistics can be corrected for the mask and
cut-sky through a window function, bypassing the need to compute linear terms
that were introduced for the previous-generation non-Gaussianity statistics,
such as the skewness estimator. We discus the ratio A_{NL} =
\tau_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary
models and discuss the physical significance of each statistic. Using these
estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the
cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL} and find -7.4 <
g_{NL}/10^5 < 8.2 and -0.6 < \tau_{NL}/10^4 < 3.3 improving the previous
COBE-based limit on \tau_{NL} < 10^8 nearly four orders of magnitude with WMAP.Comment: 15 pages. 14 figure
Local non-Gaussianity from inflation
The non-Gaussian distribution of primordial perturbations has the potential
to reveal the physical processes at work in the very early Universe. Local
models provide a well-defined class of non-Gaussian distributions that arise
naturally from the non-linear evolution of density perturbations on
super-Hubble scales starting from Gaussian field fluctuations during inflation.
I describe the delta-N formalism used to calculate the primordial density
perturbation on large scales and then review several models for the origin of
local primordial non-Gaussianity, including the cuvaton, modulated reheating
and ekpyrotic scenarios. I include an appendix with a table of sign conventions
used in specific papers.Comment: 21 pages, 1 figure, invited review to appear in Classical and Quantum
Gravity special issue on non-linear and non-Gaussian cosmological
perturbation
Scale-dependent non-Gaussianity probes inflationary physics
We calculate the scale dependence of the bispectrum and trispectrum in
(quasi) local models of non-Gaussian primordial density perturbations, and
characterize this scale dependence in terms of new observable parameters. They
can help to discriminate between models of inflation, since they are sensitive
to properties of the inflationary physics that are not probed by the standard
observables. We find consistency relations between these parameters in certain
classes of models. We apply our results to a scenario of modulated reheating,
showing that the scale dependence of non-Gaussianity can be significant. We
also discuss the scale dependence of the bispectrum and trispectrum, in cases
where one varies the shape as well as the overall scale of the figure under
consideration. We conclude providing a formulation of the curvature
perturbation in real space, which generalises the standard local form by
dropping the assumption that f_NL and g_NL are constants.Comment: 27 pages, 2 figures. v2: Minor changes to match the published versio
On the divergences of inflationary superhorizon perturbations
We discuss the infrared divergences that appear to plague cosmological
perturbation theory. We show that within the stochastic framework they are
regulated by eternal inflation so that the theory predicts finite fluctuations.
Using the formalism to one loop, we demonstrate that the infrared
modes can be absorbed into additive constants and the coefficients of the
diagrammatic expansion for the connected parts of two and three-point functions
of the curvature perturbation. As a result, the use of any infrared cutoff
below the scale of eternal inflation is permitted, provided that the background
fields are appropriately redefined. The natural choice for the infrared cutoff
would of course be the present horizon; other choices manifest themselves in
the running of the correlators. We also demonstrate that it is possible to
define observables that are renormalization group invariant. As an example, we
derive a non-perturbative, infrared finite and renormalization point
independent relation between the two-point correlators of the curvature
perturbation for the case of the free single field.Comment: 12 page
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