Model-independent effects of Delta excitation in nucleon polarizabilities

Abstract

Model-independent effects of $\Delta$(1232) excitation on nucleon polarizabilities are computed in a Lorentz-invariant fashion. We find a large effect of relative order $(M_{\Delta }-M)/M$ in some of the spin polarizabilities, with the backward spin polarizability receiving the largest contribution. Similar subleading effects are found to be important in the fourth-order spin-independent polarizabilities ${\alpha }_{E\nu }$, ${\text{al}}_{E2}$, ${\text{be}}_{M\nu }$, and ${\text{be}}_{M2}$. Combining our results with those for the model-independent effects of pion loops we obtain predictions for spin and fourth-order polarizabilities which compare favorably with the results of a recent dispersion-relation analysis of data.

Comments: 14 pages, 3 figs, 4 tables; substantial revision, calculation of higher order polarizabilities included