Structure of the σ -meson and diamagnetism of the nucleon
The structure of the a meson and the diamagnetism of the nucleon are shown to be topics which are closely related to each other. Arguments are found that the γ meson couples to two photons via its non-strange qq structure component. This ansatz leads to a quantitative explanation of the t-channel component of the difference of electromagnetic polarizabilities, (α - β)t, containing the diamagnetism of the nucleon. The prediction is (α - β)t pn = (5αegπNN)/ (6π2m2fπ) = 15.3 in units of 10-4fm 3 to be compared with the experimental values (α-β) t p = 15.1±1.3 for the proton and (α-β)=14.8±2.7 for the neutron. The equivalent approach to exploit the ππstructure component of the Σ meson via the BEFT sum rule leads to (a - β)t p,n = 14 ± 2, what also is in agreement with the experimental results. Copyright © 2006 by World Scientific Publishing Co. Pvt. Ltd.