New experimental constraints on polarizability corrections to hydrogen hyperfine structure

We present a state-of-the-art evaluation of the polarizability corrections--the inelastic nucleon corrections--to the hydrogen ground-state hyperfine splitting using analytic fits to the most recent data. We find a value $\Delta_{\rm pol} = 1.3 \pm 0.3$ ppm. This is 1--2 ppm smaller than the value of $\Delta_{\rm pol}$ deduced using hyperfine splitting data and elastic nucleon corrections obtained from modern form factor fits.