Minimal Tree-Level Seesaws with a Heavy Intermediate Fermion

Abstract

There exists a generic minimal tree-level diagram, with two external scalars and a heavy intermediate fermion, that can generate naturally small neutrino masses via a seesaw. This diagram has a mass insertion on the internal fermion line, and the set of such diagrams can be partitioned according to whether the mass insertion is of the Majorana or Dirac type. We show that, once subjected to the demands of naturalness (i.e. precluding small scalar vacuum expectation values that require fine-tuning), this set is finite, and contains a relatively small number of elements. Some of the corresponding models have appeared in the literature. We present the remaining original models, thus generalizing the Type-I and Type-III seesaws, and apparently exhausting the list of their minimal non-tuned variants.

1+16 pages. v2: JHEP version (Refs added, some changes in presentation, results unchanged)

References in corpus (8)

• Triplet Scalars and Dark Matter at the LHC
• A Class of Inert N-tuplet Models with Radiative Neutrino Mass and Dark Matter
• The Higgs boson mixes with an SU(2) septet representation
• Generalized Inverse Seesaws
• Constraining models with a large scalar multiplet
• Unique Neutrino Mass Operator at any Mass Dimension
• Cascade Seesaw for Tiny Neutrino Mass
• Phenomenological constraints on minimally coupled exotic lepton triplets

Cited by in corpus (4)

• Generalized Inverse Seesaws
• A Critical Analysis of One-Loop Neutrino Mass Models with Minimal Dark Matter
• Scale-Invariant Models with One-Loop Neutrino Mass and Dark Matter Candidates
• The Simplest Models of Radiative Neutrino Mass: Excluding Simplified Zee Models and Beyond