608 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
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
de Sitter limit of inflation and nonlinear perturbation theory
We study the fourth order action of the comoving curvature perturbation in an
inflationary universe in order to understand more systematically the de Sitter
limit in nonlinear cosmological perturbation theory. We derive the action of
the curvature perturbation to fourth order in the comoving gauge, and show that
it vanishes sufficiently fast in the de Sitter limit. By studying the de Sitter
limit, we then extrapolate to the n'th order action of the comoving curvature
perturbation and discuss the slow-roll order of the n-point correlation
function.Comment: 14 pages, 1 figure; typos corrected and discussion of tensor modes
adde
The role of social media in promoting special events: acceptance of Facebook âeventsâ
This study examines Facebook âeventsâ as a medium for promoting special events to consumers. This study proposes a Social Technology Acceptance Model, an extension of the TAM model, to examine the influence of trust, expected relationships and perceived enjoyment in forming consumer attitudes towards Facebook and consumers intentions to attend an event. Data was collected through an online survey administered through special event organizerâs Facebook âPagesâ. Findings of the study suggest that usersâ trust and expected relationship through Facebook had a significant effect on usersâ acceptance of Facebook and their intended offline behaviour to attend the event. Practical and theoretical implications are discussed
Large non-Gaussianities in the Effective Field Theory Approach to Single-Field Inflation: the Bispectrum
The methods of effective field theory are used to study generic theories of
inflation with a single inflaton field and to perform a general analysis of the
associated non-Gaussianities. We investigate the amplitudes and shapes of the
various generic three-point correlators, the bispectra, which may be generated
by different classes of single-field inflationary models. Besides the
well-known results for the DBI-like models and the ghost inflationary theories,
we point out that curvature-related interactions may give rise to large
non-Gaussianities in the form of bispectra characterized by a flat shape which,
quite interestingly, is independently produced by several interaction terms. In
a subsequent work, we will perform a similar general analysis for the
non-Gaussianities generated by the generic four-point correlator, the
trispectrum.Comment: Version matching the one published in JCAP, 2 typos fixed, references
added. 30 pages, 20 figure
A parton picture of de Sitter space during slow-roll inflation
It is well-known that expectation values in de Sitter space are afflicted by
infra-red divergences. Long ago, Starobinsky proposed that infra-red effects in
de Sitter space could be accommodated by evolving the long-wavelength part of
the field according to the classical field equations plus a stochastic source
term. I argue that--when quantum-mechanical loop corrections are taken into
account--the separate-universe picture of superhorizon evolution in de Sitter
space is equivalent, in a certain leading-logarithm approximation, to
Starobinsky's stochastic approach. In particular, the time evolution of a box
of de Sitter space can be understood in exact analogy with the DGLAP evolution
of partons within a hadron, which describes a slow logarithmic evolution in the
distribution of the hadron's constituent partons with the energy scale at which
they are probed.Comment: 36 pages; uses iopart.cls and feynmp.sty. v2: Minor typos corrected.
Matches version published in JCA
Large slow-roll corrections to the bispectrum of noncanonical inflation
Nongaussian statistics are a powerful discriminant between inflationary
models, particularly those with noncanonical kinetic terms. Focusing on
theories where the Lagrangian is an arbitrary Lorentz-invariant function of a
scalar field and its first derivatives, we review and extend the calculation of
the observable three-point function. We compute the "next-order" slow-roll
corrections to the bispectrum in closed form, and obtain quantitative estimates
of their magnitude in DBI and power-law k-inflation. In the DBI case our
results enable us to estimate corrections from the shape of the potential and
the warp factor: these can be of order several tens of percent. We track the
possible sources of large logarithms which can spoil ordinary perturbation
theory, and use them to obtain a general formula for the scale dependence of
the bispectrum. Our result satisfies the next-order version of Maldacena's
consistency condition and an equivalent consistency condition for the scale
dependence. We identify a new bispectrum shape available at next-order, which
is similar to a shape encountered in Galileon models. If fNL is sufficiently
large this shape may be independently detectable.Comment: v1: 37 pages, plus tables, figures and appendices. v2: supersedes
version published in JCAP; some clarifications and more detailed comparison
with earlier literature. All results unchanged. v3:improvements to some
plots; text unchange
Large non-Gaussianities in the Effective Field Theory Approach to Single-Field Inflation: the Trispectrum
We perform the analysis of the trispectrum of curvature perturbations
generated by the interactions characterizing a general theory of single-field
inflation obtained by effective field theory methods. We find that
curvature-generated interaction terms, which can in general give an important
contribution to the amplitude of the four-point function, show some new
distinctive features in the form of their trispectrum shape-function. These
interesting interactions are invariant under some recently proposed symmetries
of the general theory and, as shown explicitly, do allow for a large value of
the trispectrum.Comment: 29 pages, 13 figure
Signatures of Planck-scale interactions in the cosmic microwave background?
Based on a rather general low-energy effective action (interacting quantum
fields in classical curved space-times), we calculate potential signatures of
new physics (such as quantum gravity) at ultra-high energies (presumably the
Planck scale) in the anisotropies of the cosmic microwave background. These
Planck-scale interactions create non-Gaussian contributions, where special
emphasis is laid on the three-point function as the most promising observable,
which also allows the discrimination between models violating and those obeying
Lorentz invariance. PACS: 98.80.Cq, 04.62.+v, 98.70.Vc, 98.80.Qc.Comment: 4 page
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