Generalized Inverse Seesaws

The seesaw mechanism can be generalized to a Type-III variant and a quintuplet variant. We present two models that provide analogous generalizations of the inverse seesaw mechanism. The first model employs a fermion triplet F ~ (1,3,0) and requires no additional multiplets or parameters relative to the standard inverse seesaw. We argue that, from a bottom-up perspective, there appears to be no particular reason to preference the usual scenario over this variant. The second model employs a fermion quintuplet F ~ (1,5,0) and requires an additional scalar S ~ (1,4,1). We also show that minimal inverse seesaws with even larger fermionic representations are not expected to realize naturally small neutrino masses.