We compute the decoupling constant ζ<inf>m</inf> relating light quark masses of effective n<inf>l</inf>-flavour QCD to (n<inf>l</inf>+1)-flavour QCD to four-loop order. Immediate applications are the evaluation of the MS- charm quark mass with five active flavours and the bottom quark mass at the scale of the top quark or even at GUT scales. With the help of a low-energy theorem ζ<inf>m</inf> can be used to obtain the effective coupling of a Higgs boson to light quarks with five-loop accuracy. We briefly discuss the influence on Γ(H→bb-).
Liu, T., & Steinhauser, M. (2015). Decoupling of heavy quarks at four loops and effective Higgs-fermion coupling. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 746, 330–334. https://doi.org/10.1016/j.physletb.2015.05.023