title: Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment from lattice QCD.
abstract: The most compelling possibility for a new law of nature beyond the four fundamental forces comprising the standard model of high-energy physics is the discrepancy between measurements and calculations of the muon anomalous magnetic moment. Until now a key part of the calculation, the hadronic light-by-light contribution, has only been accessible from models of QCD, the quantum description of the strong force, whose accuracy at the required level may be questioned. A first principles calculation with systematically improvable errors is needed, along with the upcoming experiments, to decisively settle the matter. For the first time, the form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in such a framework, lattice QCD+QED and QED. A nonperturbative treatment of QED is used and checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed for which statistically significant signals are obtained. Initial results are promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.
authors.affiliation: Physics Department, University of Connecticut, Storrs, Connecticut 06269-3046, USA and RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Blum
authors.affiliation: Physics Department, University of Connecticut, Storrs, Connecticut 06269-3046, USA.
authors.forename: Saumitra
authors.initials: S
authors.lastname: Chowdhury
authors.affiliation: Department of Physics, Nagoya University, Nagoya 464-8602, Japan and Nishina Center, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Hayakawa
authors.affiliation: RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973, USA and Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Taku
authors.initials: T
authors.lastname: Izubuchi