Type-II seesaw triplet scalar effects on neutrino trident scattering.

In Type-II seesaw model, an electroweak triplet scalar field Δ with a non-zero vacuum expectation value (vev) v Δ is introduced to facilitate the generation of small neutrino masses. A non-zero v Δ also affects the W mass through the electroweak ρ parameter, making it to be less than 1 as predicted by standard model (SM). The component fields in Δ come along introduce additional contributions to reduce the SM rare neutrino trident scattering cross section. These fields also induce new processes not existed in SM, such as l i → l j ‾ l k l l and l i → l j γ. There are severe constraints on these processes which limit the effects on neutrino trident scattering and the ρ parameter and therefore the W mass. The newly measured W mass by CDF makes the central value of ρ parameter to be larger than 1, even larger than previously expected. Combining neutrinoless double beta decay, direct neutrino mass and oscillation data, we find a lower limit for v Δ as a function of the triplet scalar mass m Δ , v Δ > (6.3 ∼ 8.4) eV (100 GeV / m Δ). To have significant effect on ρ in this model, v Δ needs to be in the range of a GeV or so. However this implies a very small m Δ which is ruled out by data. We conclude that the effect of triplet vev v Δ on the W mass can be neglected. We also find that at 3 σ level, the deviation of the ratio for Type-II Seesaw to SM neutrino trident scattering cross section predictions is reduced to be below 1, but is restricted to be larger than 0.98. [ABSTRACT FROM AUTHOR]