1,107 research outputs found
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
A non-Gaussian landscape
Primordial perturbations with wavelengths greater than the observable universe shift the effective background fields in our observable patch from their global averages over the inflating space. This leads to a landscape picture where the properties of our observable patch depend on its location and may significantly differ from the expectation values predicted by the underlying fundamental inflationary model. We show that if multiple fields are present during inflation, this may happen even if our horizon exit would be preceded by only a few e-foldings of inflation. Non-Gaussian statistics are especially affected: for example models of local non-Gaussianity predicting |f_NL|>> 10 over the entire inflating volume can have a probability up to a few tens of percent to generate a non-detectable bispectrum in our observable patch |fNL^{obs.}|<10. In this work we establish systematic connections between the observable local properties of primordial perturbations and the global properties of the inflating space which reflect the underlying high energy physics. We study in detail the implications of both a detection and non-detection of primordial non-Gaussianity by Planck, and discover novel ways of characterising the naturalness of different observational configurations
The trispectrum in ghost inflation
We calculate the trispectrum in ghost inflation where both the contact
diagram and scale-exchange diagram are taken into account. The shape of
trispectrum is discussed carefully and we find that the local form is absent in
ghost inflation. In general, for the non-local shape trispectrum there are not
analogous parameters to and which can
completely characterize the size of local form trispectrum.Comment: 19 pages, 8 figures; clarifications and corrections added, 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
Scale-dependence of Non-Gaussianity in the Curvaton Model
We investigate the scale-dependence of f_NL in the self-interacting curvaton
model. We show that the scale-dependence, encoded in the spectral index
n_{f_NL}, can be observable by future cosmic microwave background observations,
such as CMBpol, in a significant part of the parameter space of the model. We
point out that together with information about the trispectrum g_NL, the
self-interacting curvaton model parameters could be completely fixed by
observations. We also discuss the scale-dependence of g_NL and its implications
for the curvaton model, arguing that it could provide a complementary probe in
cases where the theoretical value of n_{f_NL} is below observational
sensitivity.Comment: 14 pages, 5 figures, Eq.(10) correcte
Curvaton and the inhomogeneous end of inflation
We study the primordial density perturbations and non-Gaussianities generated
from the combined effects of an inhomogeneous end of inflation and curvaton
decay in hybrid inflation. This dual role is played by a single isocurvature
field which is massless during inflation but acquire a mass at the end of
inflation via the waterfall phase transition. We calculate the resulting
primordial non-Gaussianity characterized by the non-linearity parameter,
, recovering the usual end-of-inflation result when the field decays
promptly and the usual curvaton result if the field decays sufficiently late.Comment: 13 pages, 5 figure
The Trispectrum in the Multi-brid Inflation
The trispectrum is at least as important as the bispectrum and its size can
be characterized by two parameters and . In this short
paper, we focus on the Multi-brid inflation, in particular the two-brid
inflation model in arXiv.0805.0974, and find that is always
positive and roughly equals to for the low scale
inflation, but can be negative or positive and its order of magnitude
can be the same as that of or even largerComment: 12 pages; minor correction, refs added; further refs added, version
for publication in JCA
Trispectrum from Ghost Inflation
Ghost inflation predicts almost scale-invariant primordial cosmological
perturbations with relatively large non-Gaussianity. The bispectrum is known to
have a large contribution at the wavenumbers forming an equilateral triangle
and the corresponding nonlinear parameter is typically of
order . In this paper we calculate trispectrum from ghost inflation
and show that the corresponding nonlinear parameter is typically of
order . We investigate the shape dependence of the trispectrum and see
that it has some features different from DBI inflation. Therefore, our result
may be useful as a template to distinguish ghost inflation from other models of
inflation by future experiments.Comment: 25 pages, 10 figure
Revisiting donkey anaphora in Mandarin Chinese: A reply to Pan and Jiang (2015)
Theoretical and Experimental Linguistic
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