Direct photon production by positive- and negative-pion beams

Large-p/sub T/ direct photon production by ..pi../sup - +/ beams in the framework of QCD is studied in detail. Higher-order corrections (K factors), photon bremsstrahlung, partons' intrinsic transverse momentum, and higher-twist effects are taken into account. The various ambiguities which beset a theoretical calculation are carefully considered. Comparisons with all available data and further predictions are presented in detail. At fixed energy the ratio of the inclusive cross sections by ..pi../sup -/ and ..pi../sup +/ shows a clear increase with p/sub T/. Certain preliminary data do not support this prediction. It is concluded that precise measurements of this ratio offer an important test of QCD.