Two-photon decays and transition form factors of π0 , η , and η′ in large- Nc chiral perturbation theory

P Bickert,S Scherer

doi:10.1103/physrevd.102.074019

Abstract

We present a calculation of $P\to \gamma^{(\ast)}\gamma^{(\ast)}$ processes, where $P=\pi^0,\ \eta,\ \eta'$, at the one-loop level up to and including next-to-next-to-leading order (NNLO) in large-$N_c$ chiral perturbation theory. The results are numerically evaluated successively at LO, NLO, and NNLO. The appearing low-energy constants are determined through fits to the available experimental data. We investigate the decay widths to real photons, the single-virtual transition form factors, and the widths of $P\to\gamma l^+l^-$, where $l=e,\ \mu$. Furthermore, we provide results for the slopes and curvatures of the transition form factors.

Highlights

In recent years, the two-photon interaction of the light pseudoscalar mesons has received considerable attention from both the experimental and theoretical sides [1]
We present a calculation of P → γðÃÞγðÃÞ processes, where P 1⁄4 π0; η; η0, at the one-loop level up to and including next-to-next-to-leading order (NNLO) in large-Nc chiral perturbation theory
The low-energy regime of QCD is characterized by an interplay between the dynamical breaking of chiral symmetry, the explicit symmetry breaking by the quark masses, and the axial Uð1ÞA anomaly

Summary

Introduction

The two-photon interaction of the light pseudoscalar mesons has received considerable attention from both the experimental and theoretical sides [1]. The largest uncertainty in the anomalous magnetic moment aμ originates from the evaluation of hadronic contributions, namely, the hadronic vacuum polarization and the hadronic light-by-light (HLbL) scattering [3]. In this context, the two-photon decays of the light pseudoscalars enter the HLbL contribution in terms of pseudoscalar-exchange diagrams The two-photon decays of the light pseudoscalars enter the HLbL contribution in terms of pseudoscalar-exchange diagrams

Objectives

Discussion

Conclusion