V.D39 — CnuB echo surface

The CnuB echo surface Sigma_{CnuB} = H_partial[omega]|_{n=n_nu} is the boundary holonomy algebra at the neutrino decoupling depth, encoding the neutrino energy spectrum (Fermi-Dirac at T_nu), the number of neutrino species (3 from A-sector structure), and their mass spectrum.