## [astro-ph/0207664] Stable clustering, the halo model and nonlinear cosmological power spectra

 Authors: R.E. Smith (Edinburgh, Nottingham), J.A. Peacock (Edinburgh), A. Jenkins (Durham), S.D.M. White (MPA), C.S. Frenk (Durham), F.R. Pearce (Nottingham), P.A. Thomas (Sussex), G. Efstathiou (IoA), H.M.P. Couchmann (McMaster), The Virgo Consortium Abstract: We present the results of a large library of cosmological N-body simulations, using power-law initial spectra. The nonlinear evolution of the matter power spectra is compared with the predictions of existing analytic scaling formulae based on the work of Hamilton et al. The scaling approach has assumed that highly nonlinear structures obey stable clustering' and are frozen in proper coordinates. Our results show that, when transformed under the self-similarity scaling, the scale-free spectra define a nonlinear locus that is clearly shallower than would be required under stable clustering. Furthermore, the small-scale nonlinear power increases as both the power-spectrum index n and the density parameter Omega decrease, and this evolution is not well accounted for by the previous scaling formulae. This breakdown of stable clustering can be understood as resulting from the modification of dark-matter haloes by continuing mergers. These effects are naturally included in the analytic halo model' for nonlinear structure; using this approach we are able to fit both our scale-free results and also our previous CDM data. This approach is more accurate than the commonly-used Peacock--Dodds formula and should be applicable to more general power spectra. Code to evaluate nonlinear power spectra using this method is available from this http URL Following publication, we will make the power-law simulation data available through the Virgo website this http URL [PDF]  [PS]  [BibTex]  [Bookmark]

Discussion related to specific recent arXiv papers
Sarah Bridle
Posts: 144
Joined: September 24 2004
Affiliation: University College London (UCL)
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### [astro-ph/0207664] Stable clustering, the halo model and non

This paper (the Smith et al HaloFit paper) says:
"our preliminary investigations show that the present formalism should cope naturally with spectra containing a realistic degree of baryonic features"
Does anyone know of any updates on this? esp is it OK to input a linear theory matter power spectrum containing baryon wiggles (e.g. from CMBFAST, CAMB etc) into HaloFit? (e.g. as implemented by "nonlinear_pk = F" in CAMB).

Pirin Erdogdu
Posts: 5
Joined: December 17 2004
Affiliation: UCL

### [astro-ph/0207664] Stable clustering, the halo model and non

Hey Sarah,
You are probably aware of this but CAMB now has an option which applies non-linear corrections to power spectrum from HALOFIT. And if it is CAMB, it must be correct!!!
Also Figure 6 in astro-ph/0607061 shows a comparison of the halofit power spectrum with the one calculated from n-body simulations using full boltzmann equations. They say the fit is not great but it looks pretty good to me! so I guess it depends on what you want to do.