Fuzzy Dark Matter from Infrared Confining Dynamics

TL;DR

This paper proposes a new model for fuzzy dark matter involving infrared confining dynamics, predicting observable cosmological effects and potential terrestrial tests, offering an alternative to string theory-based mechanisms.

Contribution

It introduces a concrete dynamical model for fuzzy dark matter with a scale from infrared confining dynamics, differing from string instanton approaches.

Findings

Suggests a period of mild inflation from a strong first order phase transition.

Predicts a larger effective number of neutrinos, N_eff > 3.

Proposes sterile neutrinos as part of the model, testable in experiments.

Abstract

A very light boson of mass $\mathcal{O}(10^{-22})$ eV may potentially be a viable dark matter (DM) candidate which can avoid phenomenological problems associated with cold DM. Such "fuzzy DM (FDM)" may naturally be an axion with a decay constant $f_a \sim 10^{16} \div 10^{18}$ GeV, and a mass $m_a \sim \mu^2/f_a$ with $\mu\sim 10^2$ eV. Here we propose a concrete model where $\mu$ arises as a dynamical scale from infrared confining dynamics, analogous to QCD. Our model is an alternative to the usual approach of generating $\mu$ through string theoretic instanton effects. We outline the features of this scenario that result from various cosmological constraints. We find that those constraints are suggestive of a period of mild of inflation, perhaps from a strong first order phase transition, that reheats the Standard Model (SM) sector only. A typical prediction of our scenario, broadly speaking, is a larger effective number of neutrinos compared to the SM value $N_{\text{eff}} \approx 3$, as inferred from precision measurements of the cosmic microwave background. Some of the new degrees of freedom may be identified as "sterile neutrinos," which may be required to explain certain neutrino oscillation anomalies. Hence, aspects of our scenario could be testable in terrestrial experiments, which is a novelty of our FDM model.