Type II Seesaw Higgsology and LEP/LHC constraints

TL;DR

This paper investigates the phenomenology of light scalar states in the type II seesaw model, analyzing constraints from LEP and LHC data, and explores potential signatures like invisible Higgs decays and charged scalar effects.

Contribution

It provides a detailed analysis of LEP and LHC constraints on light scalars in the type II seesaw model, highlighting regions compatible with neutrino mass generation and potential collider signatures.

Findings

Light scalars with masses 44-80 GeV can evade LEP limits under certain conditions.

Decays of the 125 GeV Higgs into light scalars can produce signatures mimicking dark matter.

Constraints on doubly-charged scalars are crucial for testing the model's viability.

Abstract

In the {\sl type II seesaw} model, if spontaneous violation of the lepton number conservation prevails over that of explicit violation, a rich Higgs sector phenomenology is expected to arise with light scalar states having mixed charged-fermiophobic/neutrinophilic properties. We study the constraints on these light CP-even ($h^0$) and CP-odd ($A^0$) states from LEP exclusion limits, combined with the so far established limits and properties of the $125-126$~GeV ${\cal H}$ boson discovered at the LHC. We show that, apart from a fine-tuned region of the parameter space, masses in the $\sim 44$ to $80$ GeV range escape from the LEP limits if the vacuum expectation value of the Higgs triplet is $\lesssim {\cal O}(10^{-3})$GeV, that is comfortably in the region for 'natural' generation of Majorana neutrino masses within this model. In the lower part of the scalar mass spectrum the decay channels ${\cal H} \to h^0 h^0, A^0 A^0$ lead predominantly to heavy flavor plus missing energy or to totally invisible Higgs decays, mimicking dark matter signatures without a dark matter candidate. Exclusion limits at the percent level of these (semi-)invisible decay channels would be needed, together with stringent bounds on the (doubly-)charged states, to constrain significantly this scenario. We also revisit complementary constraints from ${\cal H} \to \gamma \gamma$ and ${\cal H} \to Z \gamma$ channels on the (doubly)charged scalar sector of the model, pinpointing non-sensitivity regions, and carry out a likeliness study for the theoretically allowed couplings in the scalar potential.