Chiral anomaly and the pion transition form factor: Beyond the cutoff

In this work, the γ→3π form factor is calculated within the Dyson-Schwinger equations framework using a contact interaction model within the so-called modified rainbow ladder truncation. The present calculation takes into account the pseudovector component in the pion Bethe-Salpeter amplitude (BSA) and π−π scattering effects, producing a γ→3π anomaly that is 1+6Rπ2 larger than the low energy prediction. Here Rπ is the relative ratio of the pseudovector and pseudoscalar components in the pion BSA; with our parameters’ input, this correction raises the γ→3π anomaly by around 10%. The main outcome of this work is the unveiling of the origin of such a correction, which could be a possible explanation of the discrepancy between the existing experimental data and the low energy prediction. Moreover, it is highlighted how the magnitude of the anomaly is affected in effective theories that require an irremovable ultraviolet cutoff. We find that for both the anomalous processes π→2γ and γ→3π, the missing contribution to the anomaly can be compensated by the additional structures related with the quark anomalous magnetic moment. Published by the American Physical Society 2024

QCD anomalies in electromagnetic processes: A solution to the γ→3π puzzle

Xing,

Dang,

Sultan

et al. 2024

Electromagnetic and two-photon transition form factors of the pseudoscalar mesons: An algebraic model computation

Higuera-Angulo,

Hernández-Pinto,

Raya

et al. 2024

We compute electromagnetic and two-photon transition form factors of ground-state pseudoscalar mesons: π,K,ηc,ηb. To this end, we employ an algebraic model based upon the coupled formalism of Schwinger-Dyson and Bethe-Salpeter equations. Within this approach, the dressed quark propagator and the relevant Bethe-Salpeter amplitude encode the internal structure of the corresponding meson. Electromagnetic properties of the meson are probed via the quark-photon interaction. The algebraic model employed by us unifies the treatment of all ground-state pseudoscalar mesons. Its parameters are carefully fitted performing a global analysis of existing experimental data including the knowledge of the charge radii of the mesons studied. We then compute and predict electromagnetic and two-photon transition form factors for a wide range of probing photon momentum-squared which is of direct relevance to the experimental observations carried out thus far or planned at different hadron physics facilities such as the Thomas Jefferson National Accelerator Facility (JLab) and the forthcoming Electron-Ion Collider. We also present comparisons with other theoretical models and approaches and lattice quantum chromodynamics. Published by the American Physical Society 2024

Gravitational form factors of pseudoscalar mesons in a contact interaction

Sultan,

Xing,

Raya

et al. 2024

Given the unique role played by the gravitational form factors (GFFs) in unraveling the internal mechanics of hadrons, we examine the GFFs of ground state pseudoscalar mesons π, ηc, ηb and the hypothetical ηs(ss¯). We adopt the coupled framework of Dyson-Schwinger and Bethe-Salpeter equations within a contact interaction and employ a novel approach to the dressed amputated meson-meson scattering amplitude, which makes connection with the energy-momentum tensor and with the GFFs. The resulting GFFs fulfill the anticipated symmetry constraints. The corresponding charge and mass radii and the D term are also computed. We show that the D term for the pseudoscalar mesons is bounded within the (−1,−1/3) range; these bounds correspond to the massless (chiral limit) and infinitely massive cases, respectively. Considering the current interest in the GFFs, understanding the D term of pseudoscalar mesons and their GFFs can provide an important first step for future endeavors in the field. Published by the American Physical Society 2024