Third-order QCD corrections to the charged-current structure function F3F3

We compute the coefficient function for the charge-averaged W±W±-exchange structure function F3F3 in deep-inelastic scattering (DIS) to the third order in massless perturbative QCD. Our new three-loop contribution to this quantity forms, at not too small values of the Bjorken variable x  , the dominant part of the next-to-next-to-next-to-leading order corrections. It thus facilitates improved determinations of the strong coupling αsαs and of 1/Q21/Q2 power corrections from scaling violations measured in neutrino–nucleon DIS. The expansion of F3F3 in powers of αsαs is stable at all values of x   relevant to measurements at high scales Q2Q2. At small x   the third-order coefficient function is dominated by diagrams with the colour structure dabcdabcdabcdabc not present at lower orders. At large x   the coefficient function for F3F3 is identical to that of F1F1 up to terms vanishing for x→1x→1.