Leading Electroweak Two-Loop Corrections to Precision Observables in the MSSM

The leading electroweak MSSM two-loop corrections to the electroweak precision observables are calculated. They are obtained by evaluating the two-loop O(αt ), O(αtαb), O(αb) contributions to the quantity ∆ρ in the limit of heavy scalar quarks, i.e. we consider the contributions of a Two-Higgs-Doublet model with MSSM restrictions. The full analytic result for arbitrary values of the lightest CP-even Higgs boson mass is presented. The numerical effects of the leading electroweak MSSM two-loop corrections on the precision observables MW and sin 2 θeff are analyzed. The electroweak two-loop contribution to MW amounts up to −12 MeV and up to +6 × 10−5 for sin θeff . The corrections from the bottom quark loops can become important for large values of tan β. They enter with a different sign than the O(αt ) corrections. We furthermore investigate the current sensitivity of the electroweak precision observables to the top Yukawa coupling in the SM and the MSSM. The prospects for indirectly determining this coupling at the next generation of colliders are discussed. email: [email protected] email: [email protected]