Model-independent effects of Delta excitation in nucleon polarizabilities

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 $\alpha_{E\nu}$, $\al_{E2}$, $\be_{M\nu}$, and $\be_{M 2}$. 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.