Classical Nonrelativistic Effective Field Theory and the Role of Gravitational Interactions

TL;DR

This paper extends non-relativistic effective field theory to include gravitational interactions, providing a systematic way to analyze axion star stability, configuration, and lifetime without ad hoc assumptions.

Contribution

It develops a gravitationally inclusive EFT framework for axion stars, clarifies the expansion scheme, and derives stability conditions and lifetime estimates.

Findings

EFT with gravity accurately models axion star configurations.

A simple stability criterion against small perturbations is derived.

The approach enables lifetime calculations without ad hoc assumptions.

Abstract

Coherent oscillation of axions or axion-like particles may give rise to long-lived clumps, called axion stars, because of the attractive gravitational force or its self-interaction. Such a kind of configuration has been extensively studied in the context of oscillons without the effect of gravity, and its stability can be understood by an approximate conservation of particle number in a non-relativistic effective field theory (EFT). We extend this analysis to the case with gravity to discuss the longevity of axion stars and clarify the EFT expansion scheme in terms of gradient energy and Newton's constant. Our EFT is useful to calculate the axion star configuration and its classical lifetime without any ad hoc assumption. In addition, we derive a simple stability condition against small perturbations. Finally, we discuss the consistency of other non-relativistic effective field theories proposed in the literature.