J. Piekarewicz — Page 9

arXiv1993

Relativistic and Nuclear Structure Effects in Parity-Violating Quasielastic Electron Scattering

The parity violating longitudinal asymmetry ${\cal A}$ is calculated for quasielastic electron scattering. We use a variety of relativistic mean field models for the response of nuclear matter and $^{12}$C at a momentum transfer of q=550 MeV/c. Relativistic effects from a reduced nucleon mass, RPA correlations and vacuum polarization can all change ${\cal A}$ by a relatively large amount. These large nuclear structure corrections could make it impossible to extract strange quark matrix elements or radiative corrections to weak axial currents.

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arXiv1993

The Momentum Dependence of the $ρ-ω$ Mixing Amplitude in a Hadronic Model

We calculate the momentum dependence of the $ρ-ω$ mixing amplitude in a purely hadronic model. The basic assumption of the model is that the mixing amplitude is generated by $N{\bar{N}}$ loops and thus driven entirely by the neutron-proton mass difference. The value of the amplitude at the $ω$-meson point is expressed in terms of only the $NNω$ and the $NNρ$ coupling constants. Using values for these couplings constrained by empirical two-nucleon data we obtain a value for the mixing amplitude in agreement with experiment. Extending these results to the spacelike region, we find a $ρ-ω$ contribution to the NN interaction that is strongly suppressed and opposite in sign relative to the conventional contribution obtained from using the constant on-shell value for the mixing amplitude.

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