Abstract
We perform a lattice QCD calculation of the hadronic light-by-light contribution to (g-2)_mu at the SU(3) flavor-symmetric point m_pi =m_Ksimeq 420,MeV. The representation used is based on coordinate-space perturbation theory, with all QED elements of the relevant Feynman diagrams implemented in continuum, infinite Euclidean space. As a consequence, the effect of using finite lattices to evaluate the QCD four-point function of the electromagnetic current is exponentially suppressed. Thanks to the SU(3)-flavor symmetry, only two topologies of diagrams contribute, the fully connected and the leading disconnected. We show the equivalence in the continuum limit of two methods of computing the connected contribution, and introduce a sparse-grid technique for computing the disconnected contribution. Thanks to our previous calculation of the pion transition form factor, we are able to correct for the residual finite-size effects and extend the tail of the integrand. We test our understanding of finite-size effects by using gauge ensembles differing only by their volume. After a continuum extrapolation based on four lattice spacings, we obtain a_mu ^{mathrm{hlbl}}= (65.4pm 4.9 pm 6.6)times 10^{-11}, where the first error results from the uncertainties on the individual gauge ensembles and the second is the systematic error of the continuum extrapolation. Finally, we estimate how this value will change as the light-quark masses are lowered to their physical values.
Highlights
Acterizes the deviation of g from this reference value by a = (g − 2) /2
The ability of quantum electrodynamics (QED) to quantitatively predict this observable played a crucial role in establishing quantum field theory as the framework in which particle physics theories are formulated
Our approach for determining aμhlbl is based on coordinatespace perturbation theory where the QED elements of the Feynman diagrams yielding aμhlbl are precomputed in infinite volume, and only the four-point amplitude of the electromagnetic current is computed on the lattice
Summary
The achieved experimental precision on the measurement of the anomalous magnetic moment of the muon [1], aμ, is 540 ppb At this level of precision, such a measurement tests QED, and the effects of the weak and the strong interaction of the Standard Model (SM) of particle physics. There exists a tension of about 3.7 standard deviations between the SM prediction and the experimental measurement. The status of this test of the SM is reviewed in [2,3,4,5]. Only the TFF of the η remains independent and is largely unknown at the SU(3)f -symmetric point, experimental information is available for the two-photon decay width (which provides the coupling strength to two real photons) and some experimental results are available for the singly as well as the doubly-virtual form factor [13,14,15], only for relatively large virtualities above 1.5 GeV2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
