Hadronic light-by-light scattering in the anomalous magnetic moment of the muon

Asmussen, Nils; Gérardin, Antoine; Nyffeler, Andreas; Meyer, Harvey B.

doi:10.21468/scipostphysproc.1.031

Cited by 16 publications

(21 citation statements)

References 33 publications

(58 reference statements)

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“…The most accurate determination comes from the use of e + e − → hadrons data via a dispersion relation, although lattice QCD calculations have made significant progress in computing this quantity from first principles [5,8]. The hadronic light-by-light (HLbL) scattering contribution a hlbl μ , which is of third order in α, currently contributes at a comparable level to the theory uncertainty budget and is being addressed both by dispersive and lattice methods; see [9][10][11] and references therein.…”

Section: Introductionmentioning

confidence: 99%

Hadronic light-by-light contribution to $$(g-2)_\mu $$ from lattice QCD with SU(3) flavor symmetry

et al. 2020

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We perform a lattice QCD calculation of the hadronic light-by-light contribution to $$(g-2)_\mu $$ ( g - 2 ) μ at the SU(3) flavor-symmetric point $$m_\pi =m_K\simeq 420\,$$ m π = m K ≃ 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 $$a_\mu ^{\mathrm{hlbl}}= (65.4\pm 4.9 \pm 6.6)\times 10^{-11}$$ a μ hlbl = ( 65.4 ± 4.9 ± 6.6 ) × 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.

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Section: Introductionmentioning

confidence: 99%

Hadronic light-by-light contribution to $$(g-2)_\mu $$ from lattice QCD with SU(3) flavor symmetry

et al. 2020

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“…Since the HVP contribution can be systematically calculated with a data-driven dispersive approach [5-9], lattice QCD [10][11][12][13][14][15][16], and potentially be accessed independently by the proposed MUonE experiment [17,18], which aims to measure the space-like finestructure constant α(t) in elastic electron-muon scattering, the HLbL contribution may end up dominating the theoretical error. 1 Apart from lattice QCD [27][28][29], recent data-driven approaches towards HLbL scattering are again rooted in dispersion theory, either for the HLbL tensor [30][31][32][33][34][35], the Pauli 1 Note that higher-order insertions of HVP [5,19,20] and HLbL [21] are already under sufficient control, as are hadronic corrections in the anomalous magnetic moment of the electron, where recently a 2.5 σ tension between the direct measurement [22] and the SM prediction [23] using the fine-structure constant from Cs interferometry [24] emerged [25,26].…”

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confidence: 99%

Longitudinal short-distance constraints for the hadronic light-by-light contribution to (g − 2)μ with large-Nc Regge models

Colangelo

Hagelstein

Hoferichter

et al. 2020

J. High Energ. Phys.

278

164

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While the low-energy part of the hadronic light-by-light (HLbL) tensor can be constrained from data using dispersion relations, for a full evaluation of its contribution to the anomalous magnetic moment of the muon (g − 2) µ also mixed-and high-energy regions need to be estimated. Both can be addressed within the operator product expansion (OPE), either for configurations where all photon virtualities become large or one of them remains finite. Imposing such short-distance constraints (SDCs) on the HLbL tensor is thus a major aspect of a model-independent approach towards HLbL scattering. Here, we focus on longitudinal SDCs, which concern the amplitudes containing the pseudoscalar-pole contributions from π 0 , η, η . Since these conditions cannot be fulfilled by a finite number of pseudoscalar poles, we consider a tower of excited pseudoscalars, constraining their masses and transition form factors from Regge theory, the OPE, and phenomenology. Implementing a matching of the resulting expressions for the HLbL tensor onto the perturbative QCD quark loop, we are able to further constrain our calculation and significantly reduce its model dependence. We find that especially for the π 0 the corresponding increase of the HLbL contribution is much smaller than previous prescriptions in the literature would imply. Overall, we estimate that longitudinal SDCs increase the HLbL contribution by ∆a LSDC µ = 13(6) × 10 −11 . A Anomalous Pseudoscalar-Vector-Vector Coupling 46 B Alternative model for pion, η, and η transition form factors 48 1 Introduction Current Standard Model (SM) evaluations of the anomalous magnetic moment of the muon, a µ = (g − 2) µ /2, differ from the value measured at the Brookhaven National Laboratory [1]a exp µ = 116 592 089(63) × 10 −11 , (1.1) by around 3.5 σ. In the near future, the new Fermilab E989 experiment [2] will be able to reduce the experimental uncertainty by a factor 4, and the E34 experiment at J-PARC [3] will provide an important cross check, see ref.[4] for a comparison of the experimental methods. Therefore, the theoretical calculation of a µ needs to be improved accordingly. The uncertainty of the SM prediction mainly stems from hadronic contributions, such as hadronic vacuum polarization (HVP), see figure 1 (a), and HLbL scattering, see figure 1 (b). Since the HVP contribution can be systematically calculated with a data-driven dispersive approach [5-9], lattice QCD [10][11][12][13][14][15][16], and potentially be accessed independently by the proposed MUonE experiment [17,18], which aims to measure the space-like finestructure constant α(t) in elastic electron-muon scattering, the HLbL contribution may end up dominating the theoretical error. 1 Apart from lattice QCD [27][28][29], recent data-driven approaches towards HLbL scattering are again rooted in dispersion theory, either for the HLbL tensor [30][31][32][33][34][35], the Pauli 1 Note that higher-order insertions of HVP [5,19,20] and HLbL [21] are already under sufficient control, as are hadronic corrections in the anomalou...

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“…For the finite-volume case, a two-pronged approach is being followed, one where the entire calculation including the QED parts is performed in finite volume (in the QED L formulation [212]) and then extrapolated to infinite volume, and a second where the QED part (essentially a two-loop integral) is done directly in infinite volume and in the continuum [213], similar to the HVP calculations. The latter approach was pioneered by the Mainz group [214,215], who have performed calculations for HLbL scattering at unphysical masses [216][217][218] but have not yet combined the two into a calculation of a µ . While the second approach eliminates the power law errors from QED, and therefore has only exponentially small errors from QCD, it suffers from larger statistical errors.…”

Section: Hadronic Light-by-light Scatteringmentioning

confidence: 99%

Opportunities for Lattice QCD in quark and lepton flavor physics

et al. 2019

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This document is one of a series of whitepapers from the USQCD collaboration. Here, we discuss opportunities for lattice QCD in quark and lepton flavor physics. New data generated at Belle II, LHCb, BES III, NA62, KOTO, and Fermilab E989, combined with precise calculations of the relevant hadronic physics, may reveal what lies beyond the Standard Model. We outline a path toward improvements of the precision of existing lattice-QCD calculations and discuss groundbreaking new methods that allow lattice QCD to access new observables.

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Hadronic light-by-light scattering in the anomalous magnetic moment of the muon

Cited by 16 publications

References 33 publications

Hadronic light-by-light contribution to $$(g-2)_\mu $$ from lattice QCD with SU(3) flavor symmetry

Hadronic light-by-light contribution to $$(g-2)_\mu $$ from lattice QCD with SU(3) flavor symmetry

Longitudinal short-distance constraints for the hadronic light-by-light contribution to (g − 2)μ with large-Nc Regge models

Opportunities for Lattice QCD in quark and lepton flavor physics

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