The see-saw portal at future Higgs factories: the role of dimension six operators

Abstract

We study an extension of the Standard Model with electroweak scale right-handed singlet fermions $N$ that induces neutrino masses, plus a generic new physics sector at a higher scale $\Lambda$. The latter is parametrized in terms of effective operators in the language of the $\nu$SMEFT. We study its phenomenology considering operators up to $d=6$, where additional production and decay modes for $N$ are present in addition to those arising from the mixing with the active neutrinos. We focus on the production with four-Fermi operators and we identify the most relevant additional decay modes to be $N\to \nu \gamma$ and $N\to 3f$. We assess the sensitivity of future Higgs factories on the $\nu$SMEFT in regions of the parameter space where the new states decay promptly, displaced or are stable on detector lengths. We show that new physics scale up to $5-60$TeV can be explored, depending on the collider considered.

30 pages, 8 figures. v2: section with theoretical bounds added, matches version accepted for publication in JHEP

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Cited by in corpus (5)

• Searches for Long-Lived Particles at the Future FCC-ee
• Assessment of the Dimension-5 Seesaw Portal and Impact of Exotic Higgs Decays on Non-Pointing Photon Searches
• Re-examining $N_R$-EFT Upto Dimension Six
• Lepton collider probes for Majorana neutrino effective interactions
• Search for the $Z^{\prime }$ boson decaying to a right-handed neutrino pair in leptophobic $\mathrm{U}(1)$ models