NUCLEAR Nuclear Physics B406 (1993) 409—422 P H V S I C S B North-Holland Reconciling dark matter, solar and atmospheric neutrinos J.T. Peltoniemi 1 and J.W.F. Valle 2 Instifuto de FIsica Corpuscular — C.S.I. C., Departament de FIsica Teôrica, Uniersitat de València, 46100 Burjassot, València, Spain Received 4 March 1993 (Revised 18 May 1993) Accepted for publication 26 May 1993 We present models that can reconcile the solar and atmospheric neutrino data with the existence of a hot dark matter component in the universe. This dark matter is a quasi-Dirac neutrino whose mass mOM arises at the one-loop level. The solar neutrino deficit is explained via nonadiabatic conversions of r’~ to a sterile neutrino v~ and the atmospheric neutrino data via maximal to ~r oscillations generated by higher order loop diagrams. For mDM 30 eV the radiative neutrino decay can lead to photons that can ionize interstellar hydrogen. In one of the models one can have observable v.~to v~ oscillation rates, with no appreciable v.~ oscillations at accelerator experiments. In addition, there can be observable rates for tau number violating processes such as i- —~ 3e and r —~e + y. In the other model one can have sizeable v~to oscillation rates, as well as sizeable rates for muon number violating processes such as /L —3 e + y, p. —~e + majoron and p. —~3e. 1. Introduction The existing hints in favour of nonzero neutrino masses include the existence of a hot dark matter component as recently suggested by COBE data and the deficits observed in the solar r’e and atmospheric v~ fluxes [1—6]. Neutrino oscillations would provide the most attractive explanation of these fluxes, which seem to be in conflict with standard theoretical expectations [7,8]. A common understanding of these data seems problematic, even at the level of simultaneously fitting the three phenomena. For example, one could have Ve r~ oscillations in the sun with 8m 2 iO~eV2, with the ~-‘~ as the hot dark matter (HDM) component (m~ few eV). However, in this scenario there is no room for oscillations to account for the E-mail 16444::PELTONIE or PELTONIE@EVALVX. Present address: SISSA, 34100 Trieste, Italy. 2 E-mail 16444: : Valle or VALLE@EVALUN1 1 0550-3213/93/$06.00 © 1993 — Elsevier Science Publishers By. All rights reserved