101 research outputs found
The Trispectrum in the Effective Field Theory of Large Scale Structure
We compute the connected four point correlation function (the trispectrum in
Fourier space) of cosmological density perturbations at one-loop order in
Standard Perturbation Theory (SPT) and the Effective Field Theory of Large
Scale Structure (EFT of LSS). This paper is a companion to our earlier work on
the non-Gaussian covariance of the matter power spectrum, which corresponds to
a particular wavenumber configuration of the trispectrum. In the present
calculation, we highlight and clarify some of the subtle aspects of the EFT
framework that arise at third order in perturbation theory for general
wavenumber configurations of the trispectrum. We consistently incorporate
vorticity and non-locality in time into the EFT counterterms and lay out a
complete basis of building blocks for the stress tensor. We show predictions
for the one-loop SPT trispectrum and the EFT contributions, focusing on
configurations which have particular relevance for using LSS to constrain
primordial non-Gaussianity.Comment: 25+3 pages, 7 figure
Partially Massless Fields During Inflation
The representation theory of de Sitter space allows for a category of
partially massless particles which have no flat space analog, but could have
existed during inflation. We study the couplings of these exotic particles to
inflationary perturbations and determine the resulting signatures in
cosmological correlators. When inflationary perturbations interact through the
exchange of these fields, their correlation functions inherit scalings that
cannot be mimicked by extra massive fields. We discuss in detail the squeezed
limit of the tensor-scalar-scalar bispectrum, and show that certain partially
massless fields can violate the tensor consistency relation of single-field
inflation. We also consider the collapsed limit of the scalar trispectrum, and
find that the exchange of partially massless fields enhances its magnitude,
while giving no contribution to the scalar bispectrum. These characteristic
signatures provide clean detection channels for partially massless fields
during inflation.Comment: 48 pages, 5 figures. v2: references added, published versio
Non-Gaussian Covariance of the Matter Power Spectrum in the Effective Field Theory of Large Scale Structure
We compute the non-Gaussian contribution to the covariance of the matter
power spectrum at one-loop order in Standard Perturbation Theory (SPT), and
using the framework of the effective field theory (EFT) of large scale
structure (LSS). The complete one-loop contributions are evaluated for the
first time, including the leading EFT corrections that involve seven
independent operators, of which four appear in the power spectrum and
bispectrum. We compare the non-Gaussian part of the one-loop covariance
computed with both SPT and EFT of LSS to two separate simulations. In one
simulation, we find that the one-loop prediction from SPT reproduces the
simulation well to 0.25 h/Mpc, while in the other simulation
we find a substantial improvement of EFT of LSS (with one free parameter) over
SPT, more than doubling the range of where the theory accurately reproduces
the simulation. The disagreement between these two simulations points to
unaccounted for systematics, highlighting the need for improved numerical and
analytic understanding of the covariance.Comment: v2 - 10+9 pages, 6 figures; minor changes + data analysis and
conclusions updated. Version accepted for publication in PR
Large scale structure from viscous dark matter
Cosmological perturbations of sufficiently long wavelength admit a fluid
dynamic description. We consider modes with wavevectors below a scale for
which the dynamics is only mildly non-linear. The leading effect of modes above
that scale can be accounted for by effective non-equilibrium viscosity and
pressure terms. For mildly non-linear scales, these mainly arise from momentum
transport within the ideal and cold but inhomogeneous fluid, while momentum
transport due to more microscopic degrees of freedom is suppressed. As a
consequence, concrete expressions with no free parameters, except the matching
scale , can be derived from matching evolution equations to standard
cosmological perturbation theory. Two-loop calculations of the matter power
spectrum in the viscous theory lead to excellent agreement with -body
simulations up to scales Mpc. The convergence properties in the
ultraviolet are better than for standard perturbation theory and the results
are robust with respect to variations of the matching scale.Comment: 30 pages, 7 figure
Higher-order statistics for DSGE models
Closed-form expressions for unconditional moments, cumulants and polyspectra of order
higher than two are derived for non-Gaussian or nonlinear (pruned) solutions to DSGE
models. Apart from the existence of moments and white noise property no distributional
assumptions are needed. The accuracy and utility of the formulas for computing
skewness and kurtosis are demonstrated by three prominent models: Smets and Wouters
(AER, 586-606, 97, 2007) (first-order approximation), An and Schorfheide (Econom.
Rev., 113-172, 26, 2007) (second-order approximation) and the neoclassical growth model
(third-order approximation). Both the Gaussian as well as Student's t-distribution are
considered as the underlying stochastic processes. Lastly, the efficiency gain of including
higher-order statistics is demonstrated by the estimation of a RBC model within a
Generalized Method of Moments framework
Non-linear dark energy clustering
We consider a dark energy fluid with arbitrary sound speed and equation of
state and discuss the effect of its clustering on the cold dark matter
distribution at the non-linear level. We write the continuity, Euler and
Poisson equations for the system in the Newtonian approximation. Then, using
the time renormalization group method to resum perturbative corrections at all
orders, we compute the total clustering power spectrum and matter power
spectrum. At the linear level, a sound speed of dark energy different from that
of light modifies the power spectrum on observationally interesting scales,
such as those relevant for baryonic acoustic oscillations. We show that the
effect of varying the sound speed of dark energy on the non-linear corrections
to the matter power spectrum is below the per cent level, and therefore these
corrections can be well modelled by their counterpart in cosmological scenarios
with smooth dark energy. We also show that the non-linear effects on the matter
growth index can be as large as 10-15 per cent for small scales.Comment: 33 pages, 7 figures. Improved presentation. References added. Matches
published version in JCA
Partially massless fields during inflation
The representation theory of de Sitter space allows for a category of partially massless particles which have no flat space analog, but could have existed during inflation. We study the couplings of these exotic particles to inflationary perturbations and determine the resulting signatures in cosmological correlators. When inflationary perturbations interact through the exchange of these fields, their correlation functions inherit scalings that cannot be mimicked by extra massive fields. We discuss in detail the squeezed limit of the tensor-scalar-scalar bispectrum, and show that certain partially massless fields can violate the tensor consistency relation of single-field inflation. We also consider the collapsed limit of the scalar trispectrum, and find that the exchange of partially massless fields enhances its magnitude, while giving no contribution to the scalar bispectrum. These characteristic signatures provide clean detection channels for partially massless fields during inflation
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