Maximal atmospheric neutrino mixing and the small ratio of muon to tau mass

We discuss the problem of the small ratio of muon mass to tau mass in a class of seesaw models where maximal atmospheric neutrino mixing is enforced through a μ–τ interchange symmetry. We introduce into those models an additional symmetry K such that m μ = 0 in the case of exact K invariance. The symmetry K may be softly broken in the Higgs potential, and one thus achieves m μ ≪ m τ in a technically natural way. We speculate on a wider applicability of this mechanism.