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 super-partners. 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 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 phenomeno-logically interesting parameter regions where H can be traded for h as the experimentally observed Higgs particle.