New interactions in neutrino oscillations with three light flavors

If one assumes solar and LSND neutrino oscillations to explain the corresponding data, then the atmospheric neutrino deficit cannot be accommodated within the Standard Model with three light flavors, unless one ignores the data’s zenith-angle dependence. We propose a novel solution to this problem by postulating large anomalous diagonal ντ -quark interactions which affect νμ − ντ oscillations traversing the Earth and induce the observed zenith-angle dependence. email: [email protected] email: [email protected] Three flavors of massless lefthanded weakly interacting neutrinos occur in the Standard Model. Experimental studies at the Large Electron Positron (LEP) collider have definitively established the number of light weak neutrino flavors to be three. However, the masslessness of any neutrino is not predicted on fundamental grounds. Beyond the Standard Model, theoretical arguments exist showing how neutrinos could acquire tiny Majorana [1] or Dirac [2] masses. On the experimental front, there is indirect evidence of small nonvanishing neutrino masses from three different kinds of phenomena pertaining to neutrino oscillations. (1) The observed depletion [3] of the solar neutrino flux from the prediction of the standard solar model in different segments of the solar neutrino energy spectrum, (2) the claimed discovery [4] of ν̄μ − ν̄e and νμ − νe oscillations by the Liquid Scintillator Neutrino Detector (LSND) experiment and (3) the deficit [5] in the atmospheric neutrino flux, measured on the ground in terms of the ratio of ratios R ≡ (νμ + ν̄μ) : (νe + ν̄e)expt./(νμ + ν̄μ) : (νe + ν̄e)MC , MC standing for the Monte-Carlo expectation – all point to nonzero neutrino masses. The canonical best fits to the data from the above three different experimental studies cannot be accommodated within the hypothesis of only three light neutrino flavors because of the three nonoverlapping ranges of δm involved. This and other considerations from astrophysics and cosmology have led to the speculation of the existence [6] of a fourth sterile (i.e. electroweak singlet) light neutrino as a possible way of reconciling all of the known data. On the other hand, if only three neutrino flavors are assumed, two of the three possible neutrino oscillations can be explained and the question is to what extent the third can be accommodated. Previous studies have chosen the exception to be either the atmospheric data [7] or the solar data [8]. A recent general analysis [9] shows that the former hypothesis is in fact favored. It seems to us that the results of the solar neutrino and the LSND experiments are quite unambiguous, assuming the absence of unknown sources of systematic error. In contrast, the detailed conclusions from the atmospheric neutrino experiment seem to depend sensitively