Chiral perturbative relation for an almost massless neutrino in the type-I seesaw mechanism

In this paper, we perform chiral perturbative analysis of an approximate lepton number symmetry associated with a sufficiently light neutrino in the type-I seesaw mechanism. For Dirac mass matrix mD=(A,B,C), linearly independent components C from A and B are treated as symmetry-breaking parameters. deviation eigenvector massless mode δu occurs first-order perturbation lightest m1or 3∝det⁡mD2/M3 emerges second-order. By solving theory, obtained specific expressions 3. As result, two complex parameters mD bounded to some extent eigenvector. These constraints not susceptible renormalization.