369 research outputs found
The constancy of \zeta in single-clock Inflation at all loops
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 show that \zeta-correlators are time-independent at large
distances at all-loop level in single clock inflation. We write the n-th order
correlators of \dot\zeta\ as the time-integral of Green's functions times the
correlators of local sources that are function of the lower order fluctuations.
The Green's functions are such that only non-vanishing correlators of the
sources at late times can lead to non-vanishing correlators for \dot\zeta\ at
long distances. When the sources are connected by high wavenumber modes, the
correlator is peaked at short distances, and these diagrams cannot lead to a
time-dependence by simple diff. invariance arguments. When the sources are
connected by long wavenumber modes one can use similar arguments once the
constancy of \zeta\ at lower orders was established. Therefore the conservation
of \zeta\ at a given order follows from the conservation of \zeta\ at the lower
orders. Since at tree-level \zeta\ is constant, this implies constancy at
all-loops by induction.Comment: 14 pages, 3 figure
The IR-resummed Effective Field Theory of Large Scale Structures
We present a new method to resum the effect of large scale motions in the
Effective Field Theory of Large Scale Structures. Because the linear power
spectrum in CDM is not scale free the effects of the large scale flows
are enhanced. Although previous EFT calculations of the equal-time density
power spectrum at one and two loops showed a remarkable agreement with
numerical results, they also showed a 2% residual which appeared related to the
BAO oscillations. We show that this was indeed the case, explain the physical
origin and show how a Lagrangian based calculation removes this differences. We
propose a simple method to upgrade existing Eulerian calculations to
effectively make them Lagrangian and compare the new results with existing fits
to numerical simulations. Our new two-loop results agrees with numerical
results up to Mpc to within 1% with no oscillatory residuals. We
also compute power spectra involving momentum which is significantly more
affected by the large scale flows. We show how keeping track of these
velocities significantly enhances the UV reach of the momentum power spectrum
in addition to removing the BAO related residuals. We compute predictions for
the real space correlation function around the BAO scale and investigate its
sensitivity to the EFT parameters and the details of the resummation technique.Comment: 37 pages, 9 figures. v2: JCAP published version, added references and
extended explanation
CMB Anisotropies from a Gradient Mode
A linear gradient mode must have no observable dynamical effect on short
distance physics. We confirm this by showing that if there was such a gradient
mode extending across the whole observable Universe, it would not cause any
hemispherical asymmetry in the power of CMB anisotropies, as long as
Maldacena's consistency condition is satisfied. To study the effect of the long
wavelength mode on short wavelength modes, we generalize the existing second
order Sachs-Wolfe formula in the squeezed limit to include a gradient in the
long mode and to account for the change in the location of the last scattering
surface induced by this mode. Next, we consider effects that are of second
order in the long mode. A gradient mode generated in Single-field inflation is shown to induce an observable
quadrupole moment. For instance, in a matter-dominated model it is equal to
. This quadrupole can be canceled
by superposition of a quadratic perturbation. The result is shown to be a
nonlinear extension of Weinberg's adiabatic modes: a long-wavelength physical
mode which looks locally like a coordinate transformation.Comment: 21+8 pages. improved presentatio
Double Soft Limits of Cosmological Correlations
Correlation functions of two long-wavelength modes with several
short-wavelength modes are shown to be related to lower order correlation
functions, using the background wave method, and independently, by exploiting
symmetries of the wavefunction of the Universe. These soft identities follow
from the non-linear extension of the adiabatic modes of Weinberg, and their
generalization by Hinterbichler et. al. The extension is shown to be unique. A
few checks of the identities are presented.Comment: 18+16 page
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