Majorana neutrinos in rare meson decays
- PDF / 667,022 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 181 Views
EMENTARY PARTICLES AND FIELDS Theory
Majorana Neutrinos in Rare Meson Decays A. Ali1) , A. V. Borisov* , and М. V. Sidorova Moscow State University, Vorob’evy gory, Moscow, 119899 Russia Received April 18, 2005; in final form, August 15, 2005
Abstract—The rare meson decays K + → π − + and D+ → K − + (, = e, µ), which are induced by Majorana neutrino exchange and which are accompanied by lepton-number nonconservation, are considered. The effects of the meson structure are taken into account on the basis of the Gaussian model for the respective Bethe–Salpeter amplitudes. It is shown that existing direct experimental constraints on the decay branching ratios are overly lenient and therefore give no way to set realistic limits on effective Majorana masses. On the basis of the constraints on the lepton-mixing parameters and neutrino masses from precision measurements of electroweak processes, neutrino-oscillation experiments, searches for neutrinoless double-beta decay of nuclei, and cosmological data, indirect constraints on the branching ratios for the decays in question are obtained and found to be much more stringent than the above direct constraints. +
+
PACS numbers : 13.20.Eb, 13.20.Fc, 14.60.Pq DOI: 10.1134/S1063778806030100
1. In recent years, oscillations of solar, atmospheric, and reactor neutrinos have been recorded in a number of experiments, including SNO, SuperKamiokande, and KamLAND (see, for example, the review articles of Bilenky [1] and Giunti and Laveder [2]). The presence of oscillations implies [3] that the neutrinos are massive particles and are mixed: the neutrino having a specific flavor ν and entering into the weak current, together with the corresponding charged lepton = e, µ, τ , is a coherent superposition of neutrino mass eigenstates νi characterized by specific masses mi ; that is, Ui νi , (1) ν = i
where Ui are elements of the lepton-mixing matrix. Experimental data on neutrino oscillations and tritium beta decay and those from searches for neutrinoless double-beta decay and from precision measurements of cosmological parameters made it possible to obtain a number of constraints on the neutrino masses and lepton-mixing parameters [2, 4, 5]. However, the neutrino-mass nature (the Dirac versus the Majorana one), which is a fundamental problem in neutrino physics, has yet to be clarified. As is well known, neutrino oscillations are insensitive to the type of mass. The Dirac neutrino carries a lepton number that distinguishes it from the corresponding 1) *
DESY, Hamburg, Germany. E-mail: [email protected]
antineutrino, and the generation mechanism for Dirac neutrino masses is identical to that for the quark and charged-lepton masses. The Majorana neutrino is a true neutral particle, which is identical to its antiparticle. The Majorana mass term in the Lagrangian does not conserve the lepton number, changing it by two units [3]. Therefore, Majorana neutrinos may induce numerous processes accompanied by lepton-number nonconservation. Searches for such processes constitute o
Data Loading...
