Relativistic and Nuclear Medium Effects on the Coulomb Sum Rule

TL;DR

This paper predicts significant quenching of the Coulomb sum rule in nuclear matter at high momentum transfers due to medium modifications of the proton form factor, highlighting QCD effects in nuclei.

Contribution

It introduces a quantum field-theoretic quark-level approach that incorporates QCD symmetries to predict medium effects on the Coulomb sum rule, differing from previous models.

Findings

Dramatic quenching of Coulomb sum rule at high momentum transfer

Proton Dirac form factor modifications drive the effect

Results differ from quantum Monte Carlo calculations for carbon

Abstract

In light of the forthcoming high precision quasielastic electron scattering data from Jefferson Lab, it is timely for the various approaches to nuclear structure to make robust predictions for the associated response functions. With this in mind, we focus here on the longitudinal response function and the corresponding Coulomb sum rule for isospin-symmetric nuclear matter at various baryon densities. Using a quantum field-theoretic quark-level approach which preserves the symmetries of quantum chromodynamics, as well as exhibiting dynamical chiral symmetry breaking and quark confinement, we find a dramatic quenching of the Coulomb sum rule for momentum transfers $\left|\mathbf{q}\right| \gtrsim 0.5\,$GeV. The main driver of this effect lies in changes to the proton Dirac form factor induced by the nuclear medium. Such a dramatic quenching of the Coulomb sum rule was not seen in a recent quantum Monte Carlo calculation for carbon, suggesting that the Jefferson Lab data may well shed new light on the explicit role of QCD in nuclei.