Constraining the Energy Momentum Tensor through DVCS Dispersion Relation beyond Leading Power

Abstract

In this letter, we analyse and interpret the kinematic power corrections to deeply virtual Compton scattering dispersion relation. We show that the kinematic corrections at twist-4 can be connected to other form factors of the Energy-Momentum Tensor beyond the pressure distribution involved at leading-power, namely the ones related to Momentum and total Angular Momentum distributions. In the nucleon case, these corrections are not negligible at presently accessible virtualities. The DVCS subtraction constant becomes an experimental constraint on momentum distributions, pressure forces distributions, and total angular momentum distributions. Finally, we use continuum and lattice-QCD results to predict the expected size of the DVCS subtraction constant, and conclude that momentum distributions are responsible of roughly one-third of the experimental signal at $Q^2 = 2\textrm{GeV}^2$.

Figures (2)

• Figure 1: Sketch of the DVCS process factorised into a hard kernel and GPDs. The incoming electron emits a virtual photon of virtuality $Q^2=-q^2$ while a real photon is detected in the final state. The total momentum transfer is $t=\Delta^2$.
• Figure 2: Upper panel: evaluation of the DVCS subtraction constant for $Q^2 = \mu^2 = 2\mathrm{GeV^2}$ using three quark flavours. CSM (lattice) calculations are shown by blue (red) curves. Continuous lines represent results obtained within the leading twist formalism; dashed lines include power corrections neglecting the second line of Eq. \ref{['eq:GFFapprox']}; finally, dashed-dotted lines include the full twist-4 correction using Eq. \ref{['eq:GFFapprox']}. The impact of HT corrections is highlighted by the corresponding band in both cases. Lower Panel: ratio between the LT description of the subtraction constant and Eq. \ref{['eq:GFFapprox']}.