Hadronic structure aspects of $K^{+}\to {\pi }^{-}+l_1^{+}+l_2^{+}$ decays

As is known from previous studies the lepton number violating decays $K^{+}\to {\pi }^{-}+l_1^{+}+l_2^{+}$ have good prospects to probe new physics beyond the standard model and provide valuable information on neutrino masses and mixing. We analyze these processes with an emphasis on their hadronic structure aspects applying the relativistic constituent quark model. We conclude that the previously ignored contribution associated with the t-channel Majorana neutrino exchange is comparable with the s-channel one in a wide range of neutrino masses. We also estimate model independent absolute upper bounds on the neutrino contributions to these decays.

Figure 1

The lowest order diagrams contributing to $K^{+}\to {\pi }^{-}{l}_1^{+}{l}_2^{+}$ decays.