17 research outputs found
Dominance of gauge artifact in the consistency relation for the primordial bispectrum
The conventional cosmological perturbation theory has been performed under
the assumption that we know the whole spatial region of the universe with
infinite volume. This is, however, not the case in the actual observations
because observable portion of the universe is limited. To give a theoretical
prediction to the observable fluctuations, gauge-invariant observables should
be composed of the information in our local observable universe with finite
volume. From this point of view, we reexamine the primordial non-Gaussianity in
single field models, focusing on the bispectrum in the squeezed limit. A
conventional prediction states that the bispectrum in this limit is related to
the power spectrum through the so-called consistency relation. However, it
turns out that, if we adopt a genuine gauge invariant variable which is
naturally composed purely of the information in our local universe, the leading
term for the bispectrum in the squeezed limit predicted by the consistency
relation vanishes.Comment: 12 pages; v2: accepted version in JCA
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
Quadra-Spectrum and Quint-Spectrum from Inflation and Curvaton Models
We calculate the quadra-spectrum and quint-spectrum, corresponding to five
and six point correlation functions of the curvature perturbation. For single
field inflation with standard kinetic term, the quadra-spectrum and
quint-spectrum are small, which are suppressed by slow roll parameters. The
calculation can be generalized to multiple fields. When there is no entropy
perturbation, the quadra-spectrum and quint-spectrum are suppressed as well.
With the presence of entropy perturbation, the quadra-spectrum and
quint-spectrum can get boosted. We illustrate this boost in the multi-brid
inflation model. For the curvaton scenario, the quadra-spectrum and
quint-spectrum are also large in the small r limit. We also calculate
representative terms of quadra-spectrum and quint-spectrum for inflation with
generalized kinetic terms, and estimate their order of magnitude for
quasi-single field inflation.Comment: 16 pages; v2: references added
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
Large non-Gaussianity from two-component hybrid inflation
We study the generation of non-Gaussianity in models of hybrid inflation with
two inflaton fields, (2-brid inflation). We analyse the region in the parameter
and the initial condition space where a large non-Gaussianity may be generated
during slow-roll inflation which is generally characterised by a large f_NL,
tau_NL and a small g_NL. For certain parameter values we can satisfy
tau_NL>>f_NL^2. The bispectrum is of the local type but may have a significant
scale dependence. We show that the loop corrections to the power spectrum and
bispectrum are suppressed during inflation, if one assume that the fields
follow a classical background trajectory. We also include the effect of the
waterfall field, which can lead to a significant change in the observables
after the waterfall field is destabilised, depending on the couplings between
the waterfall and inflaton fields.Comment: 16 pages, 6 figures; v2: comments and references added, typos
corrected, matches published versio
Primordial Trispectrum from Entropy Perturbations in Multifield DBI Model
We investigate the primordial trispectra of the general multifield DBI
inflationary model. In contrast with the single field model, the entropic modes
can source the curvature perturbations on the super horizon scales, so we
calculate the contributions from the interaction of four entropic modes
mediating one adiabatic mode to the trispectra, at the large transfer limit
(). We obtained the general form of the 4-point correlation
functions, plotted the shape diagrams in two specific momenta configurations,
"equilateral configuration" and "specialized configuration". Our figures showed
that we can easily distinguish the two different momenta configurations.Comment: 17pages, 7 figures, version to appear in JCA
Affleck-Dine baryogenesis with modulated reheating
Modulated reheating scenario is one of the most attractive models that
predict possible detections of not only the primordial non-Gaussianity but also
the tensor fluctuation through future CMB observations such as the Planck
satellite, the PolarBeaR and the LiteBIRD satellite experiments. We study the
baryonic-isocurvature fluctuations in the Affleck-Dine baryogenesis with the
modulated reheating scenario. We show that the Affleck-Dine baryogenesis can be
consistent with the modulated reheating scenario with respect to the current
observational constraint on the baryonic-isocurvature fluctuations.Comment: 7 page
Non-Gaussianity from Lifshitz Scalar
A Lifshitz scalar with the dynamical critical exponent z = 3 obtains
scale-invariant, super-horizon field fluctuations without the need of an
inflationary era. Since this mechanism is due to the special scaling of the
Lifshitz scalar and persists in the presence of unsuppressed self-couplings,
the resulting fluctuation spectrum can deviate from a Gaussian distribution. We
study the non-Gaussian nature of the Lifshitz scalar's intrinsic field
fluctuations, and show that primordial curvature perturbations sourced from
such field fluctuations can have large non-Gaussianity of order f_NL = O(100),
which will be detected by upcoming CMB observations. We compute the bispectrum
and trispectrum of the fluctuations, and discuss their configurations in
momentum space. In particular, the bispectrum is found to take various shapes,
including the local, equilateral, and orthogonal shapes. Intriguingly, all
integrals in the in-in formalism can be performed analytically.Comment: 17 pages, 15 figures, v2: published in JCA
Loop Corrections to Cosmological Perturbations in Multi-field Inflationary Models
We investigate one-loop quantum corrections to the power spectrum of
adiabatic perturbation from entropy modes/adiabatic mode cross-interactions in
multiple DBI inflationary models. We find that due to the non-canonical kinetic
term in DBI models, the loop corrections are enhanced by slow-varying parameter
and small sound speed . Thus, in general the loop-corrections
in multi-DBI models can be large. Moreover, we find that the loop-corrections
from adiabatic/entropy cross-interaction vertices are IR finite.Comment: 21 pages, 7 figures; v2, typos corrected, ref added; v3 typos
corrected, version for publishing 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