We need lab experiments to look for axion-like particles

TL;DR

The paper addresses the tension between the PVLAS-suggested ALP interpretation of a light, two-photon-coupled boson with $m_{\phi}$ and $g$ in the meV–$10^{-6}$ GeV$^{-1}$ range and stringent astrophysical bounds from solar energy loss and CAST. It proposes environment-dependent ALP models where $m_{\phi}(\mathrm{env})$ and $M_{\phi}(\mathrm{env})$ suppress ALP production in the sun via a simple step-function criterion, quantified by a suppression factor $S(R_{0})$ and compatible with PVLAS under certain conditions. The authors quantify standard bounds such as $L_{\mathrm{ALP}}=0.063\,g_{10}^{2}\,L_\odot$ and discuss how suppression can create regions in parameter space (e.g., red/green shaded areas) where PVLAS-like signals remain viable. They argue that laboratory tests, particularly light-shining-through-walls experiments like APFEL, offer a decisive probe of the PVLAS ALP hypothesis, independent of solar environments, potentially within 1–2 years.

Abstract

The PVLAS signal has renewed the interest in light bosons coupled to the electromagnetic field. However, astrophysical bounds coming from the lifetime of the sun and the CAST experiment are seemingly in conflict with this result. We discuss effective models that allow to suppress production of axion-like particles in the sun and thereby relax the bounds by some orders of magnitude. This stresses the importance of laboratory searches.

Figures (1)

• Figure 1: Various bounds on the coupling $g$ and mass $m_{\phi}$ of a (light) boson coupled to two photons (areas above single lines are excluded). The green vertically shaded strip gives the range of all reasonable axion models. The two lines within its boundaries give a typical KSVZ and DFSZ model. The green and red diagonally shaded areas give the additional area allowed when we suppress the production of ALP's in the sun (the green smaller one is a little bit more conservative).