Loop neutrino masses from d=7 operator

Understand

We discuss the generation of small neutrino masses from d=7 1-loop diagrams.

• We first systematically analyze all possible d=7 1-loop topologies.
• There is a total of 48 topologies, but only 8 of these can lead to "genuine" d=7 neutrino masses.
• Here, we define genuine models to be models in which neither d=5 nor d=7 tree-level masses nor a d=5 1-loop mass appear, such that the d=7 1-loop is the leading order contribution to the neutrino masses.