Cosmological parameters from large scale structure - geometric versus shape information

TL;DR

This paper examines how geometric and shape information from large scale structure surveys independently influence cosmological parameter estimation, highlighting the dominant role of geometric data in simple models and the importance of shape data in complex models.

Contribution

It introduces a new dewiggling method for analyzing the matter power spectrum and clarifies the roles of shape and geometric information in different cosmological models.

Findings

Shape information is less impactful than geometric information in simple LambdaCDM models.

Shape data becomes crucial in extended models with extra light particles or variable dark energy.

Current neutrino mass limits are primarily driven by geometric information, not small-scale power suppression.

Abstract

The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of these two types of information on cosmological parameter estimation, and show that for the simplest cosmological models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features. An immediate corollary is that contrary to popular beliefs, the upper limit on the neutrino mass m_\nu presently derived from LSS combined with cosmic microwave background (CMB) data does not in fact arise from the possible small-scale power suppression due to neutrino free-streaming, if we limit the model framework to minimal LambdaCDM+m_\nu. However, in more complicated models, such as those extended with extra light degrees of freedom and a dark energy equation of state parameter w differing from -1, shape information becomes crucial for the resolution of parameter degeneracies. This conclusion will remain true even when data from the Planck surveyor become available. In the course of our analysis, we introduce a new dewiggling procedure that allows us to extend consistently the use of the SDSS HPS to models with an arbitrary sound horizon at decoupling. All the cases considered here are compatible with the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.