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Home Brief CV – Research – Teaching Outreach Conferences Software Press Links Search Portal external: Higgs WG LHC and Philosophy | Research interests:
Supersymmetry at higher orders↳Supersymmetry (SUSY) is one of the prime candidates for the theory beyond the ↳Standard Model. It solves some of the most severe problems of the Standard Model, above all the so-called ↳fine-tuning problem.
Higgs mass in SupersymmetryThe ↳Minimal Supersymmetric extension of the Standard Model (MSSM) contains five physical ↳Higgs bosons whose masses are determined by only two SUSY parameters at lowest order in ↳perturbation theory. Radiative corrections soften this constraint and lead to relations among the Higgs boson masses and other SUSY parameters. Therefore, a precise measurement of one or more of these masses allows for stringent tests of the MSSM. We have calculated the lightest Higgs boson mass at three-loop level as a function of the other SUSY parameters [5], [7]. To our knowledge, this is the first observable which is known to this order in SUSY.Matching conditions for the strong coupling constantSUSY exhibits the remarkable feature of so-called ↳gauge coupling unification. This means that the three (energy dependent) gauge couplings of the strong, the weak, and the electromagnetic interaction are equal at one particular energy value MGUT. However, this value is about a trillion times larger than what will be achieved at the ↳Large Hadron Collider. Nevertheless, assuming that the SUSY parameters are known, one can predict the value of this unification energy very precisely. On the other hand, the requirement of unification allows one to restrict the parameter space of supersymmetry.The energy-dependence of the coupling constants is determined by ↳renormalization group equations and threshold matching conditions. In Ref. [1], we evaluated the matching conditions for the strong coupling at two-loop level, while the three-loop beta function was calculated in 6 (see also [ref]). This provides the most precise prediction of MGUT. Similar relations hold for the quark masses. In Ref. [4], we evaluated the energy dependence of the strong coupling and the bottom quark mass in the MSSM at three-loop level. Dimensional ReductionAs is the case for any field theory in general, quantum effects in SUSY lead to divergences which need to be regularized. In a non-supersymmetric theory, this can be done most efficiently by working in a D-dimensional space-time at intermediate steps of the calculation, and letting D→4 at the end. This procedure is called ↳Dimensional Regularization (DREG). However, since altering the number of space-time dimensions from 4 to D leads to a mismatch between the fermionic and the bosonic degrees of freedom, DREG breaks supersymmetry explicitely.For this reason, an alternative method to DREG has been suggested long ago, so called Dimensional Reduction (DRED) [ref]. Conversion formulas between the DRED and the DREG scheme have been evaluated at two-loop order in Ref. [2], and at three-loop order in Ref. [3].
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