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Lattice Calculation of Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment
The quark-connected part of the hadronic light-by-light scattering contribution to the muon’s anomalous magnetic moment is computed using lattice QCD with chiral fermions.
We report several significant algorithmic improvements and demonstrate their effectiveness through specific calculations which show a reduction in statistical errors by more than an order of magnitude. The most realistic of these calculations is performed with a near-physical, 139 MeV pion mass on a (5.5 fm)³ spatial volume using the 48³ × 96 Iwasaki gauge ensemble of the RBC/UKQCD Collaboration
Factorization Theorem Relating Euclidean and Light-Cone Parton Distributions
In a large-momentum nucleon state, the matrix element of a gauge-invariant
Euclidean Wilson line operator accessible from lattice QCD can be related to
the standard light-cone parton distribution function through the large-momentum
effective theory (LaMET) expansion. This relation is given by a factorization
theorem with a non-trivial matching coefficient. Using the operator product
expansion we prove the large-momentum factorization of the quasi-parton
distribution function in LaMET, and show that the more recently discussed
Ioffe-time distribution approach also obeys an equivalent factorization
theorem. Explicit results for the coefficients are obtained and compared at
one-loop. Our proof clearly demonstrates that the matching coefficients in the
scheme depend on the large partonic momentum rather than
the nucleon momentum.Comment: 19 pages, 4 figure