Sum rule for the backward spin polarizability of the nucleon from a backward dispersion relation

Abstract

A new sum rule for ${\gamma }_{\pi }$, the backward spin polarizability of the nucleon, is derived from a backward-angle dispersion relation. Taking into account single- and multi-pion photoproduction in the s-channel up to the energy 1.5 GeV and resonances in the t-channel with mass below 1.5 GeV, it is found for the proton and neutron that $[{\gamma }_{\pi }{]}_p$ = -39.5 +/- 2.4 and $[{\gamma }_{\pi }{]}_n$ = 52.5 +/- 2.4, respectively, in units of 10^{-4} fm^4.

Comments: 10 pages, 1 figure, revtex. Submitted to Phys. Lett. B