Neutrino Spectroscopy with atoms

In this paper, two atomic processes, neutrino-less double electron capture (0νεε) and radiative emission of neutrino pair (RENP), are described. The 0νεε process has the same physics objective as the neutrino-less double beta-decay, and thus its observation proves non-conservation of the total lepton number and the rate measurement would provide information on the effective neutrino mass. The RENP process is sensitive to the neutrino absolute mass scale, the mass hierarchy pattern, the mass type (Majorana or Dirac), and the CP violating phases. Its key idea is to amplify otherwise small rates of |e〉→|g〉+γ+ν_iν_j (with ν_i, ν_j mass eigenstates), by developing the macro-coherent medium polarization among target atoms strongly coupled to fields inside the medium. Experiments using these two processes are now being planned to reveal nature of neutrinos.