Scalar mesons and polarizability of the nucleon

Abstract

It is shown that the scalar mesons $\sigma$, $f_0(980)$ and $a_0(980)$ as $t$-channel exchanges quantitatively solve the problem of diamagnetism and give an explanation of the large missing part of the electric polarizability $\alpha$ showing up when only the pion cloud is taken into account. The electric polarizability of the proton $\alpha_p$ confirms a two-photon width of the $\sigma$ meson of $\Gamma_{\sigma\gamma\gamma}=(2.58\pm 0.26)$ keV.