Light Front Nuclear Theory and the HERMES Effect

Abstract

I discuss the use of light cone variables to compute the nucleonic and mesonic components of nuclear wave functions. A Lagrangian and its energy-momentum tensor $T^{^+\mu}$ is used to define the total momentum operators $P^\mu$. The aim is to use wave functions, expressed in terms of plus-momentum variables, which are used to analyze high energy experiments such as deep inelastic scattering, Drell-Yan production, (e,e') and (p,p') reactions. We discuss infinite nuclear matter within the mean field approximation; finite nuclei using the mean field approximation; nucleon-nucleon scattering, within the one boson exchange approximation; and, infinite nuclear matter including the effects of two-nucleon correlations. Standard good results for nuclear saturation properties are obtained, with a possible improvement in the lowered value, 180 MeV, of the computed nuclear compressibility. In our approach, manifest rotational invariance emerges at the end of the calculation. Thus nuclear physics can be done in a manner in which modern nuclear dynamics can be implemented and symmetries are respected. A salient feature is that $\omega,\sigma$ and $\pi$ mesons are obtained as important constituents. These can contribute coherently to enhance nuclear electroproduction cross sections for longitudinal virtual photons at low $Q^2$, while depleting the cross section for transverse photons. Thus the recent HERMES inelastic lepton-nucleus scattering data at low $Q^2$ and small $x$ can be described using photon-meson and meson-nucleus couplings which are consistent with constraints obtained from meson decay widths, nuclear structure, deep inelastic scattering, and lepton pair production data. Our model makes a variety of testable predictions.