Abstract
In scenarios with sterile (right-handed) neutrinos that are subject to an approximate "lepton-number-like" symmetry, the heavy neutrinos (i.e. the mass eigenstates) can have masses around the electroweak scale and couple to the Higgs boson with, in principle, unsuppressed Yukawa couplings while accounting for the smallness of the light neutrinos' masses. In these scenarios, the on-shell production of heavy neutrinos and their subsequent decays into a light neutrino and a Higgs boson constitutes a hitherto unstudied resonant contribution to the Higgs production mechanism. We investigate the relevance of this resonant mono-Higgs production mechanism in leptonic collisions, including the present experimental constraints on the neutrino Yukawa couplings, and we determine the sensitivity of future lepton colliders to the heavy neutrinos. With Monte Carlo event sampling and a simulation of the detector response we find that, at future lepton colliders, neutrino Yukawa couplings below the percent level can lead to observable deviations from the SM and, furthermore, the sensitivity improves with higher center-of-mass energies (for identical integrated luminosities).
Highlights
Renormalisable terms for neutrino masses can be introduced when righthanded neutrinos are added to the field content of the SM
In scenarios with sterile neutrinos that are subject to an approximate “lepton-number-like” symmetry, the heavy neutrinos can have masses around the electroweak scale and couple to the Higgs boson with, in principle, unsuppressed Yukawa couplings while accounting for the smallness of the light neutrinos’ masses
We investigate the relevance of this resonant mono-Higgs production mechanism in leptonic collisions, including the present experimental constraints on the neutrino Yukawa couplings, and we determine the sensitivity of future lepton colliders to the heavy neutrinos
Summary
As mentioned in the introduction, it is possible to have sterile (right-handed) neutrinos with masses around the electroweak (EW) scale and unsuppressed (up to O(1)) Yukawa couplings, when a “lepton-number-like” symmetry is realized in the theory. The relevant features of seesaw models with such a protective symmetry may be represented in a benchmark scenario, which we refer to as the “symmetry protected seesaw scenario” (SPSS) (see [9]) in the following
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