Axion searches with helioscopes and astrophysical signatures for axion(-like) particles

Axions should be produced copiously in stars such as the Sun. The first part of this paper reviews the capabilities and performance of axion helioscopes. The mechanism they rely on is described and the experimental results for the interaction of solar axions and axion-like particles with matter are given. The second part is actually observationally driven. New results obtained with Monte Carlo simulation reconstruct solar observations, previously dismissed, supporting an axion(-like) involvement with m a ≈1–2 × 10 −2 eV c −2 . To further quantify the suggested solar observations as being originated by axions, additional theoretical work is needed. However, the recently suggested axion interaction with magnetic field gradients is a generic theoretical example that seems to reconcile for the first time current limits, derived from axion helioscopes, and potential axion-related solar x-ray activity, thus avoiding contradictions with the best experimental limits. Magnetic quadrupoles can be used to experimentally test this idea, thus becoming a new catalyst in axion experiments. Finally, a short outlook for the future is given, in view of the experimental expansion of axion research with the state-of-the-art orbiting x-ray observatories.