Neutrinoless double beta decay

The status of the search for neutrinoless double beta decay is reviewed. The effort to reach the sensitivity needed to cover the effective Majorana neutrino mass corresponding to the degenerate and inverted mass hierarchy is described. Various issues concerning the theory (and phenomenology) of the relation between the $0\nu\beta\beta$ decay rate and the absolute neutrino mass scale are discussed, in particular the issue of mechanism of the $0\nu\beta\beta$ decay. Finally, the relation between the neutrino magnetic moments and the charge conjugation property (Dirac vs. Majorana) is described.Comment: Lecture notes at TASI2006, Boulder, CO, June 2006; to be published in proceeding

Nuclear structure and double beta decay

Study of the neutrinoless double beta decay, $0\nu\beta\beta$, includes a variety of problems of nuclear structure theory. They are reviewed here. The problems range from the mechanism of the decay, i.e. exchange of the light Majorana neutrino neutrino versus the exchange of some heavy, so far unobserved particle. Next, the proper expressions for the corresponding operator are described that should include the effects of the nucleon size and of the recoil order terms in the hadronic current. The issue of proper treatment of the short range correlations, in particular for the case of the heavy particle exchange, is discussed also. The variety of methods employed these days in the theoretical evaluation of the nuclear matrix elements $M^{0\nu}$ is briefly described and the difficulties causing the spread and hence uncertainty in the values of $M^{0\nu}$ are discussed. Finally, the issue of the axial current quenching, and of the resonance enhancement in the case of double electron capture are described.Comment: Review paper accepted for publication in the special issue of J. Phys. G: Nucl. Phys. devoted to the double beta deca

Conversion of electron spectrum associated with fission into the antineutrino spectrum

The accuracy of the procedure that converts the experimentally determined electron spectrum associated with fission of the nuclear fuels ^{235}U, ^{239}Pu, ^{241}Pu, and ^{238}U into the $\bar{\nu}_e$ spectrum is examined. By using calculated sets of mutually consistent spectra it is shown that the conversion procedure can result in a small $\sim$1% error provided several conditions are met. Chief among them are the requirements that the average nuclear charge as a function of the $\beta$ decay endpoint energy is independently known and that the $\bar{\nu}_e$ spectrum is binned into bins that are several times larger than the width of the slices used to fit the electron spectrum.Comment: Accepted for publication in Phys. Rev.

Evaluation of reactor neutrino flux: issues and uncertainties

Evaluation of the reactor $\bar{\nu}_e$ flux and spectrum is an essential ingredient of their application in the neutrino oscillation studies. Two anomalies, i.e. discrepancies between the observed and expected count rates, are widely discussed at the resent time. The total rate is $\sim$ 6\% lower than the expectation at all distances $>$ 10 m from the reactor. And there is a shoulder (often referred to as "bump") at neutrino energies 5-7 MeV, not predicted in the calculated spectrum. I review the ways the flux and spectrum is evaluated and concentrate on the error budget. I argue that far reaching conclusions based on these anomalies should await a thorough understanding of the uncertainties of the spectrum, and point out possible standard physics sources of the anomalies.Comment: Talk presented at NuPhys2015 (London, 16-18 December 2015). 8 pages, LaTeX, 2 pdf figure