Ultralight Dirac neutrinos from nearly degenerate Higgs doublets

Two Higgs doublets respect a mirror symmetry with spontaneous violation so that their vacuum expectation values can realize a small difference. Under this symmetry, three newly introduced right-handed neutrinos rather than the standard model fermions perform an odd transformation. Accordingly the neutrino masses and the charged fermion masses respectively are proportional to the difference and sum of the vacuum expectation values of two Higgs doublets. From a phenomenological perspective, such nearly degenerate Higgs doublets with large cancellation are equivalent to a Dirac seesaw mechanism with high suppression.