Precise prediction of the MSSM Higgs boson masses for low MA

Precise predictions for Higgs boson masses in the Minimal Supersymmetric Standard Model can be obtained by combining fixed-order calculations with effective field theory (EFT) methods for the resummation of large logarithms in case of heavy superpartners. This hybrid approach is implemented in the computer code FeynHiggs and has been applied in previous studies for calculating the mass of the lightest CP-even Higgs boson for low, intermediate and high SUSY scales. In these works it was assumed that the non-standard Higgs bosons share a common mass scale with the supersymmetric squark particles, leaving the Standard Model as the low-energy EFT. In this article, we relax this restriction and report on the implemention of a Two-Higgs-Doublet Model (THDM) as effective theory below the SUSY scale into our hybrid approach. We explain in detail the various steps how our EFT calculation is consistently combined with the fixed-order calculation within the code FeynHiggs. In our numerical investigation we find effects on the mass of the lightest CP-even Higgs boson h of up to 9 GeV in scenarios with low $M_A$ , low $\tan\beta$ and high SUSY scales, when compared with previous versions of FeynHiggs. Comparisons to other publicly available pure EFT codes with a THDM show good agreement. Effects on the mass of the second lightest CP-even Higgs boson H are found to be negligible in the phenomenologically interesting parameter regions where H can be traded for h as the experimentally observed Higgs particle.