The Weinberg operator is the unique dimension-5 operator that generates Majorana masses for
neutrinos after electroweak symmetry breaking. Thus, it seems natural that the way to have
small neutrino masses is that they are Majorana particles, with their masses obtained at tree level
suppressed by a heavy scale, i.e. the seesaw mechanism. We consider new dimension-5 operators
with additional scalars that transform under higher representations R under SU(2), up to R ≤ 5.
We analyse the constraints on the VEVs of the new scalar multiplets from the 𝜌 parameter, as well
as the generation of dimension-6 operators and non-unitarity constraints