The muon g-2 discrepancy: new physics or a relatively light Higgs?

After a brief review of the muon g-2 status, we discuss hypothetical errors in the Standard Model prediction that might explain the present discrepancy with the experimental value. None of them seems likely. In particular, a hypothetical increase of the hadroproduction cross section in low-energy e+e- collisions could bridge the muon g-2 discrepancy, but it is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 135GeV which, in conjunction with the experimental 114.4GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.