The muon g-2 and the bounds on the Higgs boson mass
Abstract
After a brief review of the muon g-2 status, we analyze the possibility that the present discrepancy between experiment and the Standard Model (SM) prediction may be due to hypothetical errors in the determination of the hadronic leading-order contribution to the latter. In particular, we show how an increase of the hadro-production cross section in low-energy e+e- collisions could bridge the muon g-2 discrepancy, leading however to a decrease on the electroweak upper bound on MH, the SM Higgs boson mass. That bound is currently MH < ~ 150GeV (95%CL) based on the preliminary top quark mass Mt = 172.6(1.4)GeV and the recent determination α had(5)(MZ) = 0.02768(22), while the direct-search lower bound is MH > 114.4GeV (95%CL). By means of a detailed analysis we conclude that this solution of the muon g-2 discrepancy is unlikely in view of current experimental error estimates. However, if this turns out to be the solution, the 95%CL upper bound on MH is reduced to about 130GeV which, in conjunction with the experimental lower bound, leaves a narrow window for the mass of this fundamental particle.