OFF-SHELL ELECTROMAGNETIC FORM-FACTORS OF PIONS AND KAONS IN CHIRAL PERTURBATION-THEORY

The off-shell electromagnetic vertex of a (pseudo) scalar particle con tains, in general, two form factors F and G which depend, in addition to the squared momentum transfer, on the invariant masses associated w ith the initial and final legs of the vertex. Chiral perturbation theo ry to one loop is used to calculate the off-shell form factors of pion s and kaons. The formalism of Gasser and Leutwyler, which was previous ly used to calculate the on-shell limit of the form factor F, is exten ded to accommodate the most general form for off-shell Green's functio ns in the pseudoscalar meson sector. We find that chiral symmetry pred icts that the form factors F of the charged pions and kaons go off-she ll in the same way, i.e., the off-shell slope at the real photon point is given by the same new phenomenological constant beta1. Furthermore , it is shown that at order p4 the form factor F of the K0 does not sh ow any off-shell dependence. The form factors G are all related to the form factors F in the correct fashion as required by the Ward-Takahas hi identity. Numerical results for different off-shell kinematics are presented.