66 research outputs found
Screening in perturbative approaches to LSS
A specific value for the cosmological constant, \Lambda, can account for
late-time cosmic acceleration. However, motivated by the so-called cosmological
constant problem(s), several alternative mechanisms have been explored. To
date, a host of well-studied dynamical dark energy and modified gravity models
exists. Going beyond \Lambda CDM often comes with additional degrees of freedom
(dofs). For these to pass existing observational tests, an efficient screening
mechanism must be in place. The linear and quasi-linear regimes of structure
formation are ideal probes of such dofs and can capture the onset of screening.
We propose here a semi-phenomenological treatment to account for screening
dynamics on LSS observables, with special emphasis on Vainshtein-type
screening.Comment: 7 pages, two figure
Exploring redshift-space distortions in large-scale structure
We explore and compare different ways large-scale structure observables in
redshift-space and real space can be connected. These include direct
computation in Lagrangian space, moment expansions and two formulations of the
streaming model. We derive for the first time a Fourier space version of the
streaming model, which yields an algebraic relation between the real- and
redshift-space power spectra which can be compared to earlier, phenomenological
models. By considering the redshift-space 2-point function in both
configuration and Fourier space, we show how to generalize the Gaussian
streaming model to higher orders in a systematic and computationally tractable
way. We present a closed-form solution to the Zeldovich power spectrum in
redshift space and use this as a framework for exploring convergence properties
of different expansion approaches. While we use the Zeldovich approximation to
illustrate these results, much of the formalism and many of the relations we
derive hold beyond perturbation theory, and could be used with ingredients
measured from N-body simulations or in other areas requiring decomposition of
Cartesian tensors times plane waves. We finish with a discussion of the
redshift-space bispectrum, bias and stochasticity and terms in Lagrangian
perturbation theory up to 1-loop order.Comment: 62 pages, 12 figure
Large-scale structure perturbation theory without losing stream crossing
We suggest an approach to perturbative calculations of large-scale clustering
in the Universe that includes from the start the stream crossing (multiple
velocities for mass elements at a single position) that is lost in traditional
calculations. Starting from a functional integral over displacement, the
perturbative series expansion is in deviations from (truncated) Zel'dovich
evolution, with terms that can be computed exactly even for stream-crossed
displacements. We evaluate the one-loop formulas for displacement and density
power spectra numerically in 1D, finding dramatic improvement in agreement with
N-body simulations compared to the Zel'dovich power spectrum (which is exact in
1D up to stream crossing). Beyond 1D, our approach could represent an
improvement over previous expansions even aside from the inclusion of stream
crossing, but we have not investigated this numerically. In the process we show
how to achieve effective-theory-like regulation of small-scale fluctuations
without free parameters.Comment: added pedagogical explanation of key math trick in appendi
A Tale of Two Scales: Screening in Large Scale Structure
The perturbative treatment of dark matter in structure formation relies on
the existence of a well-defined expansion parameter, , with
signalling the onset and ultimately the leading role of
non-linearities in the system. Cosmologies beyond the {\Lambda}CDM model often
come with additional degree(s) of freedom. The scale at which
non-linearities become important in the additional sector(s) can be rather
different from . For theories endowed with a Vainshtein-type
screening mechanism, sets the scale where screening becomes
efficient and restores continuity with the predictions of general relativity.
This is precisely the dynamics that allows such theories to pass existing
observational tests at scales where general relativity has been tested with
exquisite precision (e.g. solar system scales). We consider here the
mildly-non-linear scales of a dark matter component coupled to a galileon-type
field and focus in particular on the case of a <
hierarchy. We put forward a phenomenological framework that describes the
effects of screening dynamics on large scale structure observables.Comment: 4 pages, 1 figure, submitted to the Proceedings of the 43rd
"Rencontres de Moriond
Fast Large Scale Structure Perturbation Theory using 1D FFTs
The usual fluid equations describing the large-scale evolution of mass
density in the universe can be written as local in the density, velocity
divergence, and velocity potential fields. As a result, the perturbative
expansion in small density fluctuations, usually written in terms of
convolutions in Fourier space, can be written as a series of products of these
fields evaluated at the same location in configuration space. Based on this, we
establish a new method to numerically evaluate the 1-loop power spectrum (i.e.,
Fourier transform of the 2-point correlation function) with one-dimensional
Fast Fourier Transforms. This is exact and a few orders of magnitude faster
than previously used numerical approaches. Numerical results of the new method
are in excellent agreement with the standard quadrature integration method.
This fast model evaluation can in principle be extended to higher loop order
where existing codes become painfully slow. Our approach follows by writing
higher order corrections to the 2-point correlation function as, e.g., the
correlation between two second-order fields or the correlation between a linear
and a third-order field. These are then decomposed into products of
correlations of linear fields and derivatives of linear fields. The method can
also be viewed as evaluating three-dimensional Fourier space convolutions using
products in configuration space, which may also be useful in other contexts
where similar integrals appear.Comment: 10+4 pages, published versio
A Lagrangian effective field theory
We have continued the development of Lagrangian, cosmological perturbation
theory for the low-order correlators of the matter density field. We provide a
new route to understanding how the effective field theory (EFT) of large-scale
structure can be formulated in the Lagrandian framework and a new resummation
scheme, comparing our results to earlier work and to a series of
high-resolution N-body simulations in both Fourier and configuration space. The
`new' terms arising from EFT serve to tame the dependence of perturbation
theory on small-scale physics and improve agreement with simulations (though
with an additional free parameter). We find that all of our models fare well on
scales larger than about two to three times the non-linear scale, but fail as
the non-linear scale is approached. This is slightly less reach than has been
seen previously. At low redshift the Lagrangian model fares as well as EFT in
its Eulerian formulation, but at higher the Eulerian EFT fits the data to
smaller scales than resummed, Lagrangian EFT. All the perturbative models fare
better than linear theory.Comment: 19 pages, 3 figure
The Gaussian streaming model and Lagrangian effective field theory
We update the ingredients of the Gaussian streaming model (GSM) for the
redshift-space clustering of biased tracers using the techniques of Lagrangian
perturbation theory, effective field theory (EFT) and a generalized Lagrangian
bias expansion. After relating the GSM to the cumulant expansion, we present
new results for the real-space correlation function, mean pairwise velocity and
pairwise velocity dispersion including counter terms from EFT and bias terms
through third order in the linear density, its leading derivatives and its
shear up to second order. We discuss the connection to the Gaussian peaks
formalism. We compare the ingredients of the GSM to a suite of large N-body
simulations, and show the performance of the theory on the low order multipoles
of the redshift-space correlation function and power spectrum. We highlight the
importance of a general biasing scheme, which we find to be as important as
higher-order corrections due to non-linear evolution for the halos we consider
on the scales of interest to us.Comment: 28 pages, 5 figures. Revised to match version accepted by journa
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