  The accessibility to physics responsible for tiny neutrino mass suggests that
the mass should better originate from certain higher dimensional operators. The
conventional three types of seesaw operate at dimension five with the help of
either a new fermion or scalar multiplet. Here we propose a seesaw that
generates neutrino mass through a dimension-(5+4n) operator. The seesaw is
functioned by a fermion of isospin n+1 and zero hypercharge and a sequence of
scalar multiplets that share unity hypercharge but have isospin from 3/2 to
n+1/2 at a step of unity. Only the scalar of the highest isospin can couple to
the relevant fermions while only the scalar of the lowest isospin can directly
develop a naturally small vacuum expectation value (VEV). The VEV is then
transmitted to scalars of higher isospin through a cascading process. No global
symmetry is required to forbid lower dimensional operators. A neutrino mass of
desired order can thus be induced with a relatively low seesaw scale without
demanding too small couplings.

High Energy Physics - Phenomenology