Some consequences of a Higgs triplet

Abstract

We consider an extension of the scalar sector of the Standard Model with a single complex Higgs triplet $X$. Such extensions are the most economic, model-independent way of generating neutrino masses through triplet interactions. We show that a term like $\azero\Phi\Phi X^\dag$ must be included in the most general potential of such a scenario, in order to avoid a massless neutral physical scalar. We also demonstrate that $\azero$ must be real, thus ruling out any additional source of CP-violation. We then examine the implications of this term in the mass matrices of the singly-and doubly-charged scalar, neutral scalar and pseudoscalar fields. We find that, for small values of $\azero/\vtwo$, where $\vtwo$ is the triplet vev, the spectrum allows the decay of heavier scalars into lighter ones via gauge interactions. For large $\azero/\vtwo$, the doubly-charged, singly-charged and neutral pseudoscalar bosons become practically degenerate, while the even-parity neutral scalars remain considerably lighter, thus emphasizing the possibility of decay of the singly-charged or neutral pseudoscalar states into the neutral scalars. Constraints from the $\rho$-parameter are used to find nontrivial limits on the charged Higgs mass depending on $\azero$. We also study the couplings of the various physical states in this scenario. For small values of $|\azero|/\vtwo$, we find the lightest neutral scalar field to be triplet-dominated, and thus having extremely suppressed interactions with fermion as well as gauge boson pairs.