THE QUANTUM CORRELATION R_b-R_c IN THE MSSM: MORE HINTS OF SUPERSYMMETRY?

Abstract

We study the correlation of quantum effects on the ratios R_b and R_c within the framework of the MSSM. While in the SM the quantity R_b is in discrepancy with experiment at the 2 σlevel from below, and R_c differs from the experimental result at the 1.5 σlevel from above, the theoretical prediction for both observables could simultaneously improve in the MSSM, provided that \tanβis large enough (\tanβ\sim m_t/m_b) and there exists a light supersymmetric pseudoscalar Higgs, and also a light stop and a light chargino, all of them in the 50 GeV ballpark. In view of the masses predicted for these SUSY particles, persistence of the `R_b-R_c crisis' in the next run of experiments would not only suggest indirect evidence of SUSY, but should also encourage direct finding of SUSY at LEP 200. We also point out the consistency of this picture with other observables and the intriguing possibility that this Z-physics scenario might allow getting a hint of SUSY at Tevatron through the simple observation of t\to H^{+}b.