Figure 6: Constraints on the two-photon coupling g_{a γ} of axions and similar particles depending on their mass m_a.

Apart from the CAST limits updated with the result presented here, we show the results from the previous helioscope Sumico and the best limit from the Bragg technique (DAMA). Moreover, we show the latest limits from the laser propagation experiments OSQAR and PVLAS, high-energy photon propagation in astrophysical B -fields (H.E.S.S.), the SN1987A observation, and telescope limits for cosmic axion decay lines. Horizontal dashed lines provide limits from properties of the Sun and the energy loss of horizontal branch (HB) stars. The vertical dashed line denotes the cosmic hot dark-matter (HDM) limit which only applies to QCD axions. The haloscope limits assume that axions are the galactic dark matter. The yellow band of QCD axion models and the green KSVZ line are as in Fig. 2.