The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

TL;DR

This paper reviews the theoretical motivation, astrophysical signatures, and experimental efforts related to Weakly Interacting Slim Particles (WISPs), highlighting Europe's leading role and future prospects in discovering these potential dark matter candidates.

Contribution

It provides a comprehensive overview of WISP research, including recent experimental searches, theoretical context, and a strategic roadmap for future discoveries in Europe.

Findings

Europe leads diverse WISP search programs

Potential for transformative discoveries in the next decade

Strong theoretical and experimental motivation for WISP research

Abstract

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.