On search for eV hidden-sector photons in Super-Kamiokande and CAST experiments

If light hidden sector photons (γ′s) exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical γ′-flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to the γ-γ′ mixing strength as small as 10−5≳χ≳10−9 for the γ′ mass region 10−4≲mγ′≲10−1 eV and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments for this mass region.