/ 99 08 35 6 v 1 1 3 A ug 1 99 9 CHARGE RADII AND MAGNETIC POLARIZABILITIES OF THE ρ and K ∗ MESONS IN QCD STRING THEORY

The effective action for light mesons in the external uniform static electromagnetic fields has been obtained on the basis of QCD string theory. We argue for an area law of the Wilson loop in the presence of light quarks. The Nambu-Goto straight-line string approximation is used to simplify the problem. The Coulomb-like short-range contribution from one-gluon exchange has also been neglected. We do not take into account spin-orbital or spin-spin interactions of quarks. The formalism is use for the ρ and K * mesons. The wave function of the meson ground state is the Airy function. Using the virial theorem we estimated the mean charge radii of mesons in terms of the string tension and the zero of the Airy function. Expanding in a small external magnetic field we found the diamagnetic polarizability of ρ and K * mesons β ρ = −0.8 × 10 −4 f m 3 and β K * = −0.57 × 10 −4 f m 3 .