V.T176 — Majorana CP Phases from sigma=C_tau Constraint: phi_2 = 0

Analytic result from sigma=C_tau involution: The sigma-odd eigenstate [1,0,-1]/sqrt(2) is the charge-conjugation eigenstate with lambda=-1. For a Majorana fermion psi=C*psibar, the phase constraint e^{i*alpha}=e^{-i*alpha} requires alpha=0 or pi. Since sigma-odd = nu_middle (in normal ordering, proven V.P127), phi_Majorana(nu_2)=0. The sigma-even eigenstates phi_1, phi_3 are unconstrained by sigma alone and require full PMNS determination.