feynlag.vacuum.masses.seesaw_light_mass¶

feynlag.vacuum.masses.seesaw_light_mass(m_D, M_R)[source]¶

Light-neutrino mass matrix in the seesaw approximation M_R ≫ m_D.

Block-diagonalising seesaw_mass_matrix() for a heavy M_R gives the standard type-I result

m_ν ≈ − m_D M_R⁻¹ m_Dᵀ (symmetric, n_L × n_L),

which matches the light block of the exact Takagi diagonalisation to O(m_D²/M_R²) — verify both (dual, per CONVENTIONS.md).