Assessment of the Dimension-5 Seesaw Portal and Impact of Exotic Higgs Decays on Non-Pointing Photon Searches

TL;DR

This paper investigates the effects of dimension-5 operators in the Seesaw Portal model on heavy neutrino decays, constraints from collider data, and the potential for detecting long-lived neutrinos via exotic Higgs decays producing non-pointing photons.

Contribution

It provides a detailed recalculation of heavy neutrino decay widths, revisits experimental bounds on dipole operators, and analyzes collider signatures of long-lived neutrinos from Higgs decays.

Findings

Recalculated heavy neutrino decay widths including three-body decays.

Revised bounds on dipole operators and LEP constraints.

Projected sensitivity of non-pointing photon searches to heavy neutrino signals.

Abstract

The Dimension-5 Seesaw Portal is a Type-I Seesaw model extended by $d=5$ operators involving the sterile neutrino states, leading to new interactions between all neutrinos and the Standard Model neutral bosons. In this work we focus primarily on the implications of these new operators at the GeV-scale. In particular, we recalculate the heavy neutrino full decay width, up to three-body decays. We also review bounds on the dipole operator, and revisit LEP constraints on its coefficient. Finally, we turn to heavy neutrino pair production from Higgs decays, where the former are long-lived and disintegrate into a photon and a light neutrino. We probe this process by recasting two ATLAS searches for non-pointing photons, showing the expected event distribution in terms of arrival time $t_\gamma$ and pointing variable $|\Delta z_\gamma|$.