Cosmological parameters from large scale structure - geometric versus shape information
Jan Hamann, Steen Hannestad, Julien Lesgourgues, Cornelius Rampf, Yvonne Y. Y. Wong
TL;DR
The paper disentangles geometric BAO information from the broad-band shape of the LSS power spectrum to assess their separate impacts on cosmological parameter estimation. Using SDSS-DR7 halo power spectrum, BAO information often dominates constraints in the minimal ΛCDM+mν model, while the full shape becomes crucial in extended models with additional parameters like N_eff and w. A new dewiggling approach enables consistent use of the HPS across models, and Planck forecasts show that LSS shape can significantly improve constraints on neutrino mass and dark energy when combined with Planck data. These findings highlight the continued value of full power-spectrum information in complex cosmologies and guide future analyses of LSS data.
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models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features.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_νpresently 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_ν. 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_ν< 1.16 eV, N_eff = 4.8 \pm 2.0.