Lepton-number violation and right-handed neutrinos in Higgsless effective theories

Following previous work, we identify a symmetry S-nat that generalizes the concept of custodial symmetry, keeping under control deviations from the standard model (SM). To realize S-nat linearly, the space of gauge fields has to be extended. Covariant constraints formulated in terms of spurions reduce S-nat back to SU(2)(L)xU(1)(Y). This allows for a covariant introduction of explicit S-nat-breaking parameters. We assume that S-nat is at play in a theory of electroweak symmetry-breaking without a light Higgs particle. We describe some consequences of this assumption, using a nondecoupling effective theory in which the loop expansion procedure is based on both momentum and spurion power-counting, as in chiral perturbation theory. A hierarchy of lepton-number violating effects follows. Leading corrections to the SM are nonoblique. The effective theory includes stable light right-handed neutrinos, with an unbroken Z(2) symmetry forbidding neutrino Dirac masses. nu(R) contribution to dark matter places bounds on their masses.