IV.D198 — Koide parameter

The Koide parameter is Q = (m_e + m_mu + m_tau) / (sqrt(m_e) + sqrt(m_mu) + sqrt(m_tau))^2, a dimensionless ratio of the three charged lepton masses discovered by Yoshio Koide in 1982, experimentally equal to 0.666661 +/- 0.000007.