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Register a new userThe Implementation of the Renormalized Complex MSSM in FeynArts and FormCalc
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We describe the implementation of the renormalized complex MSSM (cMSSM) in the diagram generator FeynArts and the calculational tool FormCalc. This extension allows to perform UV-finite one-loop calculations of cMSSM processes almost fully automatically. The Feynman rules for the cMSSM with counterterms are available as a new model file for FeynArts. Also included are default definitions of the renormalization constants; this fixes the renormalization scheme. Beyond that all model parameters are generic, e.g. we do not impose any relations to restrict the number of input parameters. The model file has been tested extensively for several non-trivial decays and scattering reactions. Our renormalization scheme has been shown to give stable results over large parts of the cMSSM parameter space.
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The analysis of the Higgs search results at LEP showed that a part of the MSSM parameter space with non-zero complex phases could not be excluded, where the lightest neutral Higgs boson, h_1, has a mass of only about 45 GeV and the second lightest neutral Higgs boson, h_2, has a sizable branching fraction into a pair of h_1 states. Full one-loop results for the Higgs cascade decay h_2 --> h_1 h_1 are presented and combined with two-loop Higgs propagator corrections taken from the program FeynHiggs. Using the improved theoretical prediction to analyse the limits on topological cross sections obtained at LEP, the existence of an unexcluded region at low Higgs mass is confirmed. The effect of the genuine vertex corrections on the size and shape of this region is discussed.
We review recent progress towards automated higher-order calculations in the MSSM with complex parameters (cMSSM). The consistent renormalization of all relevant sectors of the cMSSM and the inclusion into the FeynArts/FormCalc framework has recently been completed. Some example calculations applying this framework are briefly discussed. These include two-loop corrections to cMSSM Higgs boson masses as well as partial decay widths of electroweak supersymmetric particles decaying into a Higgs boson and another supersymmetric particle.
We present new developments in FeynArts 3.9 and FormCalc 8.4, in particular the MSSMCT model file including the complete one-loop renormalization, vectorization/parallelization issues, and the interface to the Ninja library for tensor reduction.
Complete one-loop results for the decay widths of neutral Higgs bosons (h_a) into lighter neutral Higgs bosons (h_b, h_c) are presented for the MSSM with complex parameters. The results are obtained in the Feynman-diagrammatic approach, taking into account the full dependence on the spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. The genuine triple-Higgs vertex contributions are supplemented with two-loop propagator-type corrections, yielding the currently most precise prediction for this class of processes. The genuine vertex corrections turn out to be very important, yielding a large increase of the decay width compared to a prediction based on the tree-level vertex. The new results are used to analyse the impact of the experimental limits from the LEP Higgs searches on the parameter space with a very light MSSM Higgs boson. It is found that a significant part of the parameter space of the CPX benchmark scenario exists where channels involving the decay h_2 --> h_1 h_1 have the highest search sensitivity, and the existence of an unexcluded region with M_{h_1} approx 45 GeV is confirmed.
We discuss various improvements of the prediction for the light MSSM Higgs boson mass in the hybrid framework of the public code FeynHiggs, which combines fixed-order and effective field theory results. First, we discuss the resummation of logarithmic contributions proportional to the bottom-Yukawa coupling including two-loop $Delta_b$ resummation. For large $tanbeta$, these improvements can lead to large upward shifts of the Higgs mass compared to the existing fixed-order calculations. Second, we improve the implemented EFT calculation by fully taking into account the effect of $mathcal{CP}$-violating phases. As a third improvement, we discuss the inclusion of partial N$^3$LL resummation. The presented improvements will be implemented into FeynHiggs.
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