Running of $\alpha_s$ and $m_b$ in the MSSM

Understand

A consistent evolution of the strong coupling constant $\alpha_s$ from $M_Z$ to the GUT scale is presented, involving three-loop running and two-loop decoupling.

• The two-loop transition from the MS- to the DR-scheme is properly taken into account.
• In the second part of the paper, the bottom quark mass in the DR-scheme at the electroweak/SUSY scale is evaluated with four-loop accuracy.
• We find that the three-loop effects are comparable to the experimental uncertainty both for $\alpha_s$ and $m_b$.