Higher Order Corrections to the Hadronic Higgs Decay ∗

A Higgs boson in the intermediate mass range is considered. An effective Lagrangian approach is used in order to evaluate the top-induced QCD corrections of order α s to the decay into light quarks and O(α s ) corrections to the gluonic decay mode. The connection to the decoupling relations for αs and the light quark masses is discussed. The Higgs boson is the only still missing particle in the standard model. Currently only lower bounds of roughly 70 GeV have been obtained from the failure of finding the Higgs boson at the Large Electron-Positron Collider (LEP) at CERN. A global fit to the precision date also prefers a Higgs mass in the socalled intermediate mass range with MH ∼< 2MW . In this contribution we will concentrate on such a Higgs boson. The dominant decay mode is then the one into bottom quarks. In the “massless” theory corrections are known up to O(αs) [1]. In this contribution we will discuss the top-induced correction terms of the same order [2]. A second very interesting decay mode of a Higgs boson in the intermediate mass range is the decay into gluons. The lowest order process is mediated by a quark loop. It is interesting to note that in the limit where the internal quark mass is much larger than MH the amplitude gets independent of the quark mass. Therefore this process counts the number of heavy quarks. In contrast to the electroweak ρ parameter [3], the ggH coupling is also sensitive to quark isodoublets if they are mass-degenerate. The first order QCD corrections to the triangle diagram where a top quark is running around are known since long [4, 5, 6]. It turned out that the order αs corrections amount to approximately 70 %. These large corrections were a strong motivation to evaluate the next term in ∗To appear in Proceedings of the International Europhysics Conference on High Energy Physics, Jerusalem, Israel, 19-26 August 1997.