On the A-dependence of nuclear generalized parton distributions

We perform a microscopic evaluation of nuclear generalized parton distributions (GPDs) for spin-0 nuclei in the framework of the Walecka model. We demonstrate that the meson (non-nucleon) degrees of freedom dramatically influence nuclear GPDs, which is revealed in the non-trivial and unexpected A-dependence of deeply virtual Compton scattering (DVCS) observables. In particular, we find that the first moment of the nuclear D-term dA(0) ∝ A2.26, which confirms the earlier prediction of Polyakov. We find that in the HERMES kinematics, contrary to the free proton case, the nuclear meson degrees of freedom in large nuclei enhance the nuclear DVCS amplitude which becomes comparable to the Bethe–Heitler amplitude and, thus, give the non-trivial A-dependence to the DVCS asymmetries: as a function of the atomic number, the beam–charge asymmetry increases whereas the beam–spin asymmetry decreases slowly.