The muon g-2 and the bounds on the Higgs boson mass

TL;DR

This paper investigates whether errors in hadronic contributions could explain the muon g-2 discrepancy and how such explanations impact the bounds on the Higgs boson mass, concluding that current data make this unlikely but suggest a narrow mass window if true.

Contribution

It analyzes the impact of potential errors in hadronic contribution estimates on the muon g-2 discrepancy and the resulting bounds on the Higgs boson mass.

Findings

Increasing hadronic cross sections could bridge the g-2 discrepancy.

Such an increase would lower the electroweak upper bound on the Higgs mass.

Current experimental errors make this solution unlikely.

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 M_H, the SM Higgs boson mass. That bound is currently M_H < ~ 150GeV (95%CL) based on the preliminary top quark mass M_t = 172.6(1.4)GeV and the recent determination \Delta \alpha_{\rm had}^{(5)}(M_Z) = 0.02768(22), while the direct-search lower bound is M_H > 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 M_H is reduced to about 130GeV which, in conjunction with the experimental lower bound, leaves a narrow window for the mass of this fundamental particle.