Higgs radiation off top quarks in e(+)e(-) collisions

The strength of the Yukawa coupling of the leptons and quarks with the Higg s boson is uniquely determined by the Higgs mechanism for generating masses in the Standard Model. The top-Higgs coupling can be measured directly in the process e(+)e(-) --> <(tt)over bar>H. This process therefore provides a fundamental test of the Higgs mechanism. Extending earlier analyses carrie d out in the Born approximation, we have determined the cross section for t his process including QCD corrections, which turn out to be important. (C) 1998 Elsevier Science B.V. All rights reserved.