Matching the Low and High Energy Determinations of ${\alpha }_s(M_z)$ in the MSSM

Abstract

Recent calculations of supersymmetric corrections to the conflicting ratios $R_b$ and $R_c$ have shown that an alleged discrepancy between the SM predictions of these observables and the corresponding experimental values can be cured in the MSSM within a certain region of the parameter space. Here we show that, in this very same region, also a well-known discrepancy between the low and high energy determinations of ${\alpha }_s(M_Z)$ can be disposed of. Specifically, we find that the lineshape determination of the strong coupling constant, which in the SM points towards the large central value ${\alpha }_s(M_Z)\stackrel{>}{{}_{\sim }}0.125$, can be matched up with the value suggested by the wealth of low-energy data, namely ${\alpha }_s(M_Z)\simeq 0.11$, which is smaller and more in line with the traditional QCD expectations at low energy. Our approach differs from previous analyses in that we argue that the desired matching could originate to a large extent from a purely electroweak supersymmetric quantum effect.

Comments: 16 pages, LaTeX. Figures included and a few comments added. Full postscript version with figures embedded also available at ftp://ftp.ifae.es/preprint/ft/uabft365.ps