Constraints on anharmonic corrections of Fuzzy Dark Matter

TL;DR

This paper investigates how anharmonic self-interactions in fuzzy dark matter models affect cosmological evolution and structure formation, deriving constraints from CMB and large-scale structure data.

Contribution

It provides the first detailed analysis of anharmonic corrections in fuzzy dark matter, exploring their impact on matter-radiation equality and the matter power spectrum.

Findings

Anharmonic terms can cause the field to behave as radiation, altering matter-radiation equality.

Presence of anharmonicities introduces a cut-off in the matter power spectrum.

Constraints are derived from CMB and large-scale structure data using modified cosmological codes.

Abstract

The cold dark matter (CDM) scenario has proved successful in cosmology. However, we lack a fundamental understanding of its microscopic nature. Moreover, the apparent disagreement between CDM predictions and subgalactic-structure observations has prompted the debate about its behaviour at small scales. These problems could be alleviated if the dark matter is composed of ultralight fields $m \sim 10^{-22}\ \text{eV}$, usually known as fuzzy dark matter (FDM). Some specific models, with axion-like potentials, have been thoroughly studied and are collectively referred to as ultralight axions (ULAs) or axion-like particles (ALPs). In this work we consider anharmonic corrections to the mass term coming from a repulsive quartic self-interaction. Whenever this anharmonic term dominates, the field behaves as radiation instead of cold matter, modifying the time of matter-radiation equality. Additionally, even for high masses, i.e. masses that reproduce the cold matter behaviour, the presence of anharmonic terms introduce a cut-off in the matter power spectrum through its contribution to the sound speed. We analyze the model and derive constraints using a modified version of CLASS and comparing with CMB and large-scale structure data.