Scalar and pseudoscalar meson pole terms in the hadronic light-by-light contributions to $a_μ^{had}$

Abstract

Third QED order hadronic light-by-light (LBL) contributions $a_μ^{LBL}(M)$ to the anomalous magnetic moment of the muon $a_μ^{had}$ from the pole terms of scalar $σ$, $a_0(980)$ and pseudoscalar $π^0$, $η$, $η'$ mesons (M) in the framework of the linearized extended Nambu-Jona-Lasinio model are evaluated. The off-shell structure of the photon-photon-meson vertices is taken into account by means of constituent quark triangle loops. The mass of the quark is taken to be $m_u=m_d=m_q=(280 \pm 20)$ MeV. The unknown strong coupling constants of $π^0, η, η'$ and $a_0$ mesons with quarks are evaluated in a comparison of the corresponding theoretical two-photon widths calculated in the framework of our approach with experimental ones. The $σ$-meson coupling constant is taken to be equal to $π_0$-meson coupling constant as it follows from the linearized Nambu-Jona-Lasinio model Lagrangian. Then one obtains $a_μ^{LBL}(π_0)$=$(81.83 \pm 16.50) \times 10^{-11}$, $a_μ^{LBL}(η)$=$(5.62 \pm 1.25) \times 10^{-11}$, $a_μ^{LBL}(η')$=$(8.00 \pm 1.74) \times 10^{-11}$, $a_μ^{LBL}(σ)$=$(11.67 \pm 2.38) \times 10^{-11}$ and $a_μ^{LBL}(a_0)$=$(0.62 \pm 0.24) \times 10^{-11}$. The total contribution of meson poles in LBL is $a_μ^{LBL}(M)$=$(107.74 \pm 16.81) \times 10^{-11}$.