Two-loop QCD corrections to semileptonic b-quark decays near maximum recoil

Two-gluon radiative corrections to the $b\to c\mathrm{\ell }\nu$ decay width have been computed analytically as an expansion in terms of \frac{m_c}{m_b} << 1 in the kinematical limit of zero lepton invariant mass. The obtained results match smoothly with a previously known expansion around (1 - \frac{m_c}{m_b} << 1. Together they describe the process $b\to c\mathrm{\ell }\nu$ for all mass ratios \frac{m_c}{m_b}.