Axions: From Magnetars and Neutron Star Mergers to Beam Dumps and BECs

TL;DR

This review explores axion-like particles in extreme astrophysical environments, recent laboratory searches, and the potential role of Bose-Einstein Condensates in ultralight dark matter detection, highlighting new signals and experimental approaches.

Contribution

It provides a comprehensive overview of ALP signals in neutron stars, recent laboratory search techniques, and the connection between BECs and ultralight dark matter, integrating astrophysical and experimental perspectives.

Findings

Potential ALP signals in neutron star spectra identified

Laboratory beam-dump experiments discussed in detail

Properties of BECs linked to dark matter detection strategies

Abstract

We review topics in searches for axion-like-particles (ALPs), covering material that is complementary to other recent reviews. The first half of our review covers ALPs in the extreme environments of neutron star cores, the magnetospheres of highly magnetized neutron stars (magnetars), and in neutron star mergers. The focus is on possible signals of ALPs in the photon spectrum of neutron stars and gravitational wave/electromagnetic signals from neutron star mergers. We then review recent developments in laboratory-produced ALP searches, focusing mainly on accelerator-based facilities including beam-dump type experiments and collider experiments. We provide a general-purpose discussion of the ALP search pipeline from production to detection, in steps, and our discussion is straightforwardly applicable to most beam-dump type and reactor experiments. We end with a selective look at the rapidly developing field of ultralight dark matter, specifically the formation of Bose-Einstein Condensates (BECs). We review the properties of BECs of ultralight dark matter and bridge these properties with developments in numerical simulations, and ultimately with their impact on experimental searches.