The Effective Field Theory of Large Scale Structure for Mixed Dark Matter Scenarios

TL;DR

This paper develops an extension of the Effective Field Theory of Large Scale Structure to model mixed dark matter scenarios, enabling more accurate analysis of cosmological data involving non-cold dark matter components.

Contribution

It introduces a new EFT framework for coupled cold and non-cold dark matter fluctuations, including analytical solutions and a practical method for the one-loop galaxy power spectrum.

Findings

Refined constraints on ultra-light axion energy density using Planck and BOSS data.

The new model provides more accurate predictions for mixed dark matter scenarios.

Weaker bounds on axion density compared to previous studies.

Abstract

We initiate a systematic study of the perturbative nonlinear dynamics of cosmological fluctuations in dark sectors comprising a fraction of non-cold dark matter, for example ultra-light axions or light thermal relics. These mixed dark matter scenarios exhibit suppressed growth of perturbations below a characteristic, cosmologically relevant, scale associated with the microscopic nature of the non-cold species. As a consequence, the scale-free nonlinear solutions developed for pure cold dark matter and for massive neutrinos do not, in general, apply. We thus extend the Effective Field Theory of Large Scale Structure to model the coupled fluctuations of the cold and non-cold dark matter components, describing the latter as a perfect fluid with finite sound speed at linear level. We provide new analytical solutions wherever possible and devise an accurate and computationally tractable prescription for the evaluation of the one-loop galaxy power spectrum, which can be applied to probe mixed dark matter scenarios with current and upcoming galaxy survey data. As a first application of this framework, we derive updated constraints on the energy density in ultra-light axions using a combination of Planck and BOSS data. Our refined theoretical modeling leads to somewhat weaker bounds compared to previous analyses.