Nucleon spin-averaged forward virtual Compton tensor at large $Q^2$

TL;DR

This paper calculates the large-$Q^2$ behavior of the nucleon spin-averaged forward virtual Compton tensor, including full spin-2 contributions, which impacts understanding of nucleon mass differences and the proton radius puzzle.

Contribution

It provides the first complete calculation of the tensor's large-$Q^2$ behavior including spin-2 terms and corrects previous spin-0 results, advancing theoretical understanding.

Findings

Calculated the tensor's large-$Q^2$ behavior at $ u=0$

Included full spin-2 contributions for the first time

Corrected previous spin-0 contribution results

Abstract

The nucleon spin-averaged forward virtual Compton tensor determines important physical quantities such as electromagnetically-induced mass differences of nucleons, and two-photon exchange contributions in hydrogen spectroscopy. It depends on two kinematic variables: $\nu$, the virtual photon energy in the proton rest frame, and $Q^2$, the photon's invariant four-momentum squared. Using the operator product expansion, we calculate the tensor's large-$Q^2$ behavior for $\nu=0$, including for the first time the full spin-2 contribution and correcting a previous result in the literature for the spin-0 contribution. Implications for the proton radius puzzle are discussed.