Quadratic Mass Corrections of Order $\alpha_s^3 m_q^2/s$ to the Decay   Rate of Z- and W- Bosons
  We analytically compute quadratic mass corrections of order $\alpha_s^3 m_q^2/s$ to the absorptive part of the (non-diagonal) correlator of two axial vector currents. This allows us to find the correction of order $\alpha_s^3 m_q^2/M^2_W$ to the $\Gamma(W -->hadrons)$ as well as similar corrections to $\Gamma(Z -->hadrons)$. 
K. G. Chetyrkin and J.H. Kuhn