Effect on Higgs Boson Decays from Large Light-Heavy Neutrino Mixing in Seesaw Models

TL;DR

This paper investigates how large light-heavy neutrino mixing in seesaw models can significantly alter Higgs boson decay patterns, potentially increasing decay widths and revealing new physics at the LHC.

Contribution

It demonstrates that sizable light-heavy neutrino mixing can enhance Higgs decay channels, offering novel experimental signatures for seesaw models of types I and III.

Findings

Higgs decay into light and heavy neutrinos can increase total Higgs width by up to 30%.

Four-body Higgs decays can be several times larger than standard model predictions.

Large mixing effects could be observable at the LHC, providing evidence for seesaw mechanisms.

Abstract

In seesaw models with more than one generation of light and heavy neutrinos, nu and N, respectively, it is possible to have sizable mixing between them for heavy-neutrino masses of order 100 GeV or less. We explore this possibility further, taking into account current experimental constraints, and study its effect on Higgs-boson decays in the contexts of seesaw models of types I and III. We find that in the type-I case the Higgs decay into a pair of light and heavy neutrinos, h -> nu N, could increase the total Higgs width in the standard model by up to almost 30% for a relatively light Higgs-boson, which would significantly affect Higgs searches at the LHC. The subsequent prompt decay of N into three light fermions makes this Higgs decay effectively a four-body decay. We further find that, in the presence of the large light-heavy mixing, these four-body Higgs decays can have rates a few times larger than their standard-model counterparts and therefore could provide a potentially important window to reveal the underlying seesaw mechanism.