Solar neutrino limit on axions and keV-mass bosons
  The all-flavor solar neutrino flux measured by the Sudbury Neutrino Observatory (SNO) constrains nonstandard energy losses to less than about 10% of the Sun's photon luminosity, superseding a helioseismological argument and providing new limits on the interaction strength of low-mass particles. For the axion-photon coupling strength we find g_a\gamma < 7E-10 1/GeV. We also derive explicit limits on the Yukawa coupling to electrons of pseudoscalar, scalar and vector bosons with keV-scale masses. 
Paolo Gondolo, Georg Raffelt