Kinematic power corrections to DVCS to twist-six accuracy

TL;DR

This paper computes higher-order power corrections in DVCS, demonstrating their convergence and impact on theoretical predictions, and confirms that target mass effects do not threaten QCD factorization in nuclear DVCS.

Contribution

It provides detailed calculations of twist-six power corrections in DVCS and shows their convergence and significance for precise QCD predictions.

Findings

Power corrections are well convergent up to |t|/Q^2 ≈ 1/4.

Organized in terms of 1/(Q^2 + t) rather than 1/Q^2.

Target mass corrections do not compromise QCD factorization.

Abstract

We calculate $(\sqrt{-t}/Q)^k $ and $(m/Q)^k$ power corrections with $k\le 4$, where $m$ is the target mass and $t$ is the momentum transfer, to several key observables in Deeply Virtual Compton Scattering (DVCS). We find that the power expansion is well convergent up to $|t|/Q^2\lesssim 1/4$ for most of the observables, but is naturally organized in terms of $1/(Q^2+t)$ rather than the nominal hard scale $1/Q^2$. We also argue that target mass corrections remain under control and do not endanger QCD factorization for coherent DVCS on nuclei. These results remove an important source of uncertainties due to the frame dependence and violation of electromagnetic Ward identities in the QCD predictions for the DVCS amplitudes in the leading-twist approximation.