Homework Statement
Give a simple estimate of the ratio of decay rates for K^+ \rightarrow e^+ \nu_e / K^+ \rightarrow \mu^+ \nu_\mu.
Homework Equations
Fermi's Golden Rule for decay width \Gamma = \hbar W = 2\pi (dn/dE_f)|M_{if}|^2.
For comparison, from the PDG, \Gamma / \Gamma_i are 1.55...