EXTENDING THE STANDARD MODEL: AN UPPER BOUND FOR A NEUTRINO MASS FROM THE RARE DECAY $K^+\rightarrow\pi^+\nu\bar\nu$

Abstract

The standard model seeming at a loss to account for the present experimental average rate for the rare decay [Formula: see text], we tackle the question with the extension of the Glashow–Salam–Weinberg model to an SU (2)L× U (1) gauge theory of J = 0 mesons proposed in Ref. 7, in which, in addition, the neutrinos are given Dirac masses from Yukawa couplings to the Higgs boson. The latter triggers a new contribution to this decay through flavor changing neutral currents that arise in the quartic term of the symmetry breaking potential; it becomes sizable for a neutrino mass in the MeV range; the experimental upper limit for the decay rate translates into an upper bound of 5.5 MeV for the mass of the neutrino, three times lower than the present direct bounds.