  Photo nuclear reactions are shown to be used for studying neutrino/weak
nuclear responses involved in astro-neutrino nuclear interactions and double
beta decays. Charged current weak responses for ground and excited states are
studied by using photo nuclear reactions through isobaric analog states of
those states, while neutral current weak responses for excited states are
studied by using photo nuclear reactions through the excited states. The weak
interaction strengths are studied by measuring the cross sections of the photo
nuclear reactions, and the spin and parity of the state are studied by
measuring angular correlations of particles emitted from the photo nuclear
reactions. Medium-energy polarized photons obtained from laser photons
scattered off GeV electrons are very useful. Nuclear responses studied by photo
nuclear reactions are used to evaluate neutrino/weak nuclear responses, i.e.
nuclear beta and double beta matrix elements and neutrino nuclear interactions,
and to verify theoretical calculations for them.
