Form factors of the Kmu3 decay in the spectator approximation of the   Standard Model
  We have calculated the parameter Ksi(0)=f-(0)/f+(0) of the Kmu3 decay in the spectator approximation of the Standard Model. It was obtained that Ksi(0) ~ -0.02. 
V.P. Efrosinin, A.N. Khotyantsev