189 research outputs found
Galilean symmetry in the effective theory of inflation: new shapes of non-Gaussianity
We study the consequences of imposing an approximate Galilean symmetry on the
Effective Theory of Inflation, the theory of small perturbations around the
inflationary background. This approach allows us to study the effect of
operators with two derivatives on each field, which can be the leading
interactions due to non-renormalization properties of the Galilean Lagrangian.
In this case cubic non-Gaussianities are given by three independent operators,
containing up to six derivatives, two with a shape close to equilateral and one
peaking on flattened isosceles triangles. The four-point function is larger
than in models with small speed of sound and potentially observable with the
Planck satellite.Comment: 23 pages, 6 figures. v2: minor changes to match JCAP published
versio
The consistency condition for the three-point function in dissipative single-clock inflation
We generalize the consistency condition for the three-point function in
single field inflation to the case of dissipative, multi-field, single-clock
models. We use the recently introduced extension of the effective field theory
of inflation that accounts for dissipative effects, to provide an explicit
proof to leading (non-trivial) order in the generalized slow roll parameters
and mixing with gravity scales. Our results illustrate the conditions necessary
for the validity of the consistency relation in situations with many degrees of
freedom relevant during inflation, namely that there is a preferred clock.
Departures from this condition in forthcoming experiments would rule out not
only single field but also a large class of multi-field models.Comment: 26+11 page
A Naturally Large Four-Point Function in Single Field Inflation
Non-Gaussianities of the primordial density perturbations have emerged as a
very powerful possible signal to test the dynamics that drove the period of
inflation. While in general the most sensitive observable is the three-point
function in this paper we show that there are technically natural inflationary
models where the leading source of non-Gaussianity is the four-point function.
Using the recently developed Effective Field Theory of Inflation, we are able
to show that it is possible to impose an approximate parity symmetry and an
approximate continuos shift symmetry on the inflaton fluctuations that allow,
when the dispersion relation is of the form , for a unique
quartic operator, while approximately forbidding all the cubic ones. The
resulting shape for the four-point function is unique. In the models where the
dispersion relation is of the form a similar construction
can be carried out and additional shapes are possible.Comment: 13 pages, 1 figure. v2: extended discussion on near-de-Sitter model
On Loops in Inflation III: Time Independence of zeta in Single Clock Inflation
Studying loop corrections to inflationary perturbations, with particular
emphasis on infrared factors, is important to understand the consistency of the
inflationary theory, its predictivity and to establish the existence of the
slow-roll eternal inflation phenomena and its recently found volume bound. In
this paper we prove that the zeta correlation function is time-independent at
one-loop level in single clock inflation. While many of the one-loop diagrams
lead to a time-dependence when considered individually, the time-dependence
beautifully cancels out in the overall sum. We identify two subsets of diagrams
that cancel separately due to different physical reasons. The first
cancellation is related to the change of the background cosmology due to the
renormalization of the stress tensor. It results in a cancellation between the
non-1PI diagrams and some of the diagrams made with quartic vertices. The
second subset of diagrams that cancel is made up of cubic operators, plus the
remaining quartic ones. We are able to write the sum of these diagrams as the
integral over a specific three-point function between two very short
wavelengths and one very long one. We then apply the consistency condition for
this three-point function in the squeezed limit to show that the sum of these
diagrams cannot give rise to a time dependence. This second cancellation is
thus a consequence of the fact that in single clock inflation the attractor
nature of the solution implies that a long wavelength zeta perturbation is
indistinguishable from a trivial rescaling of the background, and so results in
no physical effect on short wavelength modes.Comment: 47 pages, 7 figures; v2: JHEP published version, typos and minor
correction
Optimal limits on f_{NL}^{local} from WMAP 5-year data
We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP
data. Marginalizing over the amplitude of foreground templates we get -4 <
f_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses
are roughly 40% larger than these. The probability that a Gaussian simulation,
analyzed using our estimator, gives a result larger in magnitude than the one
we find is 7%. Our pipeline gives consistent results when applied to the three
and five year WMAP data releases and agrees well with the results from our own
sub-optimal pipeline. We find no evidence of any residual foreground
contamination.Comment: [v1] 21 pages, 7 figures. [v2] minor changes matching published
versio
Scale-Invariance and the Strong Coupling Problem
The effective theory of adiabatic fluctuations around arbitrary
Friedmann-Robertson-Walker backgrounds - both expanding and contracting -
allows for more than one way to obtain scale-invariant two-point correlations.
However, as we show in this paper, it is challenging to produce scale-invariant
fluctuations that are weakly coupled over the range of wavelengths accessible
to cosmological observations. In particular, requiring the background to be a
dynamical attractor, the curvature fluctuations are scale-invariant and weakly
coupled for at least 10 e-folds only if the background is close to de Sitter
space. In this case, the time-translation invariance of the background
guarantees time-independent n-point functions. For non-attractor solutions, any
predictions depend on assumptions about the evolution of the background even
when the perturbations are outside of the horizon. For the simplest such
scenario we identify the regions of the parameter space that avoid both
classical and quantum mechanical strong coupling problems. Finally, we present
extensions of our results to backgrounds in which higher-derivative terms play
a significant role.Comment: 17 pages + appendices, 3 figures; v2: typos fixe
Conformal consistency relations for single-field inflation
We generalize the single-field consistency relations to capture not only the
leading term in the squeezed limit---going as 1/q^3, where q is the small
wavevector---but also the subleading one, going as 1/q^2. This term, for an
(n+1)-point function, is fixed in terms of the variation of the n-point
function under a special conformal transformation; this parallels the fact that
the 1/q^3 term is related with the scale dependence of the n-point function.
For the squeezed limit of the 3-point function, this conformal consistency
relation implies that there are no terms going as 1/q^2. We verify that the
squeezed limit of the 4-point function is related to the conformal variation of
the 3-point function both in the case of canonical slow-roll inflation and in
models with reduced speed of sound. In the second case the conformal
consistency conditions capture, at the level of observables, the relation among
operators induced by the non-linear realization of Lorentz invariance in the
Lagrangian. These results mean that, in any single-field model, primordial
correlation functions of \zeta are endowed with an SO(4,1) symmetry, with
dilations and special conformal transformations non-linearly realized by \zeta.
We also verify the conformal consistency relations for any n-point function in
models with a modulation of the inflaton potential, where the scale dependence
is not negligible. Finally, we generalize (some of) the consistency relations
involving tensors and soft internal momenta.Comment: 26 pages, 1 figure. v2. Corrected typos, notably a sign error in eq.
(54). Matches JCAP published versio
- …