Proton Polarizability Contribution: Muonic Hydrogen Lamb Shift and Elastic Scattering

The uncertainty in the contribution to the Lamb shift in muonic hydrogen, $\Delta E^{subt}$ arising from proton polarizability effects in the two-photon exchange diagram at large virtual photon momenta is shown large enough to account for the proton radius puzzle. This is because $\Delta E^{subt}$ is determined by an integrand that falls very slowly with very large virtual photon momenta. We evaluate the necessary integral using a set of chosen form factors and also a dimensional regularization procedure which makes explicit the need for a low energy constant. The consequences of our two-photon exchange interaction for low-energy elastic lepton-proton scattering are evaluated and could be observable in a planned low energy lepton-proton scattering experiment planned to run at PSI.Comment: 12 pages, two figures. This resubmission is made to handle a problem with the function $\bar{T}_1(0,Q^2)$ pointed out by A. Walker-Loud and Paz \& Hil

Light Front Nuclear Theory and the HERMES Effect

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.Comment: Proceedings given at the conference: Relativistic Aspects of Nuclear Physics-2000, October 17-20, Tabatinga, Caraguatatuba, Brazil. Proceedings to be publishe

Color Transparency - Color Coherent Effects in Nuclear Physics

Efforts to observe color transparency in the reactions: (e,e'p), (p,pp) and coherent nuclear diffractive dissociation of pions into two jets are reviewed.Comment: Text of invited talk given at the 1997 meeting of Intersections Between Particle and Nuclear Physics, 7 pages, 1 figur