Chiral and trace anomalies in deeply virtual Compton scattering

Inspired by recent work by Tarasov and Venugopalan, we calculate the one-loop quark box diagrams relevant to polarized and unpolarized deep inelastic scattering (DIS) by introducing off-forward momentum l mu as an infrared regulator. In the polarized case, we rederive the pole 1=l2 related to the axial (chiral) anomaly. In addition, we obtain the usual logarithmic term and the DIS coefficient function. We interpret the result in terms of the generalized parton distributions (GPDs) H similar to and E similar to and discuss the possible violation of QCD factorization for the Compton scattering amplitude. Remarkably, we also find poles in the unpolarized case which are remnants of the trace anomaly. We argue that these poles are canceled by the would-be massless glueball poles in the GPDs H and E as well as in their moments, the nucleon gravitational form factors A, B and D. This mechanism sheds light on the connection between the gravitational form factors and the gluon condensate operator F mu nu F mu nu.

Automated summary

Inspired by previous work, this paper calculates one-loop quark box diagrams in polarized and unpolarized deep inelastic scattering (DIS) using off-forward momentum l_mu as an infrared regulator. The authors derive the pole 1/l^2 associated with the axial anomaly in the polarized case and obtain the logarithmic term and DIS coefficient function. The results are interpreted in terms of generalized parton distributions (GPDs) H and E, shedding light on the violation of QCD factorization and the connection between gravitational form factors and the gluon condensate operator F_mu_nu F_mu_nu. Remarkably, poles related to the trace anomaly are found in the unpolarized case but are canceled by massless glueball poles in GPDs and their moments.