QCD Corrections to Supersymmetric Higgs Boson Production: The Role of Squark Loops.

We calculate the two–loop QCD corrections to the production of the neutral supersymmetric Higgs bosons via the gluon fusion mechanism at hadron colliders, including the contributions of squark loops. To a good approximation, these additional contributions lead to the same QCD corrections as in the case where only top and bottom quark loops are taken into account. The QCD corrections are large and increase the Higgs production cross sections significantly. The search for Higgs particles is an important component of the experimental program at future high energy hadron colliders. As such it is vital to have reliable predictions for the production rates both in the Standard Model (SM) and in the minimal supersymmetric extension of the Standard Model (MSSM). The two–loop QCD corrections to the main production process, the gluon fusion mechanism [1], have been calculated in the SM in Refs. [2,3] and later generalized to the quark contributions in the MSSM [3,4]. The corrections are large and positive, increasing the production rates significantly. The MSSM requires the introduction of two Higgs doublets leading, after spontaneous symmetry breaking, to two neutral CP–even (h and H), a neutral CP–odd (A) and two charged (H ± ) Higgs particles [5]. While in the SM the dominant contribution to Higgs boson production in the gluon fusion mechanism originates from top and, to a lesser extent, bottom quark loops, in the MSSM there are additional contributions to the production of the CP– even Higgs bosons from scalar squark loops. These contributions can be neglected for very heavy squarks. However, many supergravity–inspired models predict squark (in particular stop and sbottom squark) masses significantly below 1 TeV [6]. In this case, squark loop contributions to the Higgs–gluon couplings can be of the same order, or even larger, as the standard quark contributions, as was recently stressed in Refs. [7]. In this letter, we present the O(� 3 ) QCD corrections to the cross sections �(pp ! H+X) of the fusion processes for the neutral CP–even Higgs particles H = h,H