Double beta decays and neutrino nuclear responses

Neutrino-less double beta decays (0νββ0νββ), which violate the lepton number conservation law by ΔL=2ΔL=2, are unique and realistic probes for studying the Majorana nature of neutrinos, the νν mass spectrum and the absolute mass scale, the lepton sector CP and others beyond the standard electro-weak theory. Neutrino nuclear responses (nuclear matrix elements M0νM0ν) are crucial to extract neutrino properties of the particle physics interests from experimental 0νββ0νββ rates. Subjects discussed include 0νββ0νββ processes and Majorana neutrinos, the present and future 0νββ0νββ experiments, and neutrino nuclear responses (M0νM0ν) and charge exchange reactions.