Constraining inflation with future galaxy redshift surveys

TL;DR

Future galaxy redshift surveys, combined with CMB data, significantly enhance constraints on inflationary models by improving parameter precision and enabling detection of subtle features in the primordial power spectrum.

Contribution

This paper demonstrates how upcoming galaxy surveys can complement CMB data to better constrain inflationary parameters and detect features in the primordial power spectrum.

Findings

Galaxy surveys nearly halve errors on spectral index and its running.

Adding large scale structure data improves feature constraints by over a factor of two.

Galaxy surveys can detect small amplitude oscillations undetectable by CMB alone.

Abstract

With future galaxy surveys, a huge number of Fourier modes of the distribution of the large scale structures in the Universe will become available. These modes are complementary to those of the CMB and can be used to set constraints on models of the early universe, such as inflation. Using a MCMC analysis, we compare the power of the CMB with that of the combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. We base our analysis on the Planck satellite and a spectroscopic redshift survey with configuration parameters close to those of the Euclid mission as examples. We first consider models of slow-roll inflation, and show that the inclusion of large scale structure data improves the constraints by nearly halving the error bars on the scalar spectral index and its running. If we attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached on the parameters characterizing the potential. We then study models with features in the power spectrum. In particular, we consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding large scale structures improves the constraints on features by more than a factor of two. In axion monodromy we show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.