# A coarse grained perturbation theory for the Large Scale Structure, with cosmology and time independence in the UV

## Abstract

Standard cosmological perturbation theory (SPT) for the Large Scale Structure (LSS) of the Universe fails at small scales (UV) due to strong nonlinearities and to multistreaming effects. In ref. [1] a new framework was proposed in which the large scales (IR) are treated perturbatively while the information on the UV, mainly small scale velocity dispersion, is obtained by nonlinear methods like N-body simulations. Here we develop this approach, showing that it is possible to reproduce the fully nonlinear power spectrum (PS) by combining a simple (and fast) 1-loop computation for the IR scales and the measurement of a single, dominant, correlator from N-body simulations for the UV ones. We measure this correlator for a suite of seven different cosmologies, and we show that its inclusion in our perturbation scheme reproduces the fully non-linear PS with percent level accuracy, for wave numbers up to k∼ 0.4 h Mpc{sup -1} down to 0z=. We then show that, once this correlator has been measured in a given cosmology, there is no need to run a new simulation for a different cosmology in the suite. Indeed, by rescaling this correlator by a proper function computable in SPT, the reconstruction procedure works also for the other cosmologies andmore »

- Authors:

- Kavli Institute for Cosmological Physics, Department of Astronomy and Astrophysics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States)
- School of Physics and Astronomy, University of Minnesota, Minneapolis, 55455 (United States)
- INFN, Sezione di Padova, via Marzolo 8, I-35131, Padova (Italy)
- INAF — Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34143 Trieste (Italy)

- Publication Date:

- OSTI Identifier:
- 22375860

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2014; Journal Issue: 09; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; CALCULATION METHODS; COSMOLOGY; FIELD THEORIES; NONLINEAR PROBLEMS; PERTURBATION THEORY; RED SHIFT; SIMULATION; UNIVERSE

### Citation Formats

```
Manzotti, Alessandro, Peloso, Marco, Pietroni, Massimo, Viel, Matteo, and Villaescusa-Navarro, Francisco, E-mail: manzotti.alessandro@gmail.com, E-mail: peloso@physics.umn.edu, E-mail: pietroni@pd.infn.it, E-mail: viel@oats.inaf.it, E-mail: villaescusa@oats.inaf.it.
```*A coarse grained perturbation theory for the Large Scale Structure, with cosmology and time independence in the UV*. United States: N. p., 2014.
Web. doi:10.1088/1475-7516/2014/09/047.

```
Manzotti, Alessandro, Peloso, Marco, Pietroni, Massimo, Viel, Matteo, & Villaescusa-Navarro, Francisco, E-mail: manzotti.alessandro@gmail.com, E-mail: peloso@physics.umn.edu, E-mail: pietroni@pd.infn.it, E-mail: viel@oats.inaf.it, E-mail: villaescusa@oats.inaf.it.
```*A coarse grained perturbation theory for the Large Scale Structure, with cosmology and time independence in the UV*. United States. doi:10.1088/1475-7516/2014/09/047.

```
Manzotti, Alessandro, Peloso, Marco, Pietroni, Massimo, Viel, Matteo, and Villaescusa-Navarro, Francisco, E-mail: manzotti.alessandro@gmail.com, E-mail: peloso@physics.umn.edu, E-mail: pietroni@pd.infn.it, E-mail: viel@oats.inaf.it, E-mail: villaescusa@oats.inaf.it. Mon .
"A coarse grained perturbation theory for the Large Scale Structure, with cosmology and time independence in the UV". United States.
doi:10.1088/1475-7516/2014/09/047.
```

```
@article{osti_22375860,
```

title = {A coarse grained perturbation theory for the Large Scale Structure, with cosmology and time independence in the UV},

author = {Manzotti, Alessandro and Peloso, Marco and Pietroni, Massimo and Viel, Matteo and Villaescusa-Navarro, Francisco, E-mail: manzotti.alessandro@gmail.com, E-mail: peloso@physics.umn.edu, E-mail: pietroni@pd.infn.it, E-mail: viel@oats.inaf.it, E-mail: villaescusa@oats.inaf.it},

abstractNote = {Standard cosmological perturbation theory (SPT) for the Large Scale Structure (LSS) of the Universe fails at small scales (UV) due to strong nonlinearities and to multistreaming effects. In ref. [1] a new framework was proposed in which the large scales (IR) are treated perturbatively while the information on the UV, mainly small scale velocity dispersion, is obtained by nonlinear methods like N-body simulations. Here we develop this approach, showing that it is possible to reproduce the fully nonlinear power spectrum (PS) by combining a simple (and fast) 1-loop computation for the IR scales and the measurement of a single, dominant, correlator from N-body simulations for the UV ones. We measure this correlator for a suite of seven different cosmologies, and we show that its inclusion in our perturbation scheme reproduces the fully non-linear PS with percent level accuracy, for wave numbers up to k∼ 0.4 h Mpc{sup -1} down to 0z=. We then show that, once this correlator has been measured in a given cosmology, there is no need to run a new simulation for a different cosmology in the suite. Indeed, by rescaling this correlator by a proper function computable in SPT, the reconstruction procedure works also for the other cosmologies and for all redshifts, with comparable accuracy. Finally, we clarify the relation of this approach to the Effective Field Theory methods recently proposed in the LSS context.},

doi = {10.1088/1475-7516/2014/09/047},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 09,

volume = 2014,

place = {United States},

year = {Mon Sep 01 00:00:00 EDT 2014},

month = {Mon Sep 01 00:00:00 EDT 2014}

}