O(αs) QCD and O(αew) electroweak corrections to t(-)over-barth0 production in γ γ collision

We calculate the O(alpha(s)) QCD and O(alpha(ew)) electroweak one-loop corrections in the Standard Model framework, to the production of an intermediate Higgs boson associated with tt pair via gammagamma fusion at an electron-positron linear collider (LC). We find the O(alpha(s)) QCD corrections can be larger than the O(alpha(ew)) electroweak ones, with the variations of the Higgs boson mass m(h) and e(+)e(-) colliding energy roots. Both corrections may significantly decrease or increase the Born cross section. The numerical results show that the relative corrections from QCD to the process e(+)e(-) --> gammagamma --> tth(0) may reach 34.8%, when roots = 800 GeV and m(h) = 200 GeV, while those from electroweak can be -13.1, -15.8 and -12.0%, at roots = 800 GeV, 1 TeV and 2 TeV, respectively. (C) 2004 Elsevier B.V. All rights reserved.