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The off-shell electromagnetic vertex of a (pseudo-) scalar particle contains,in general, two form factors F and G which depend, in addition to the squaredmomentum transfer, on the invariant masses associated with the initial andfinal legs of the vertex. Chiral perturbation theory to one loop is used tocalculate the off-shell form factors of pions and kaons. The formalism ofGasser and Leutwyler, which was previously used to calculate the on-shell limitof the form factor F, is extended to accommodate the most general form foroff-shell Green's functions in the pseudoscalar meson sector. We find thatchiral symmetry predicts that the form factors F of the charged pions and kaonsgo off-shell in the same way, i.e., the off-shell slope at the real photonpoint is given by the same new phenomenological constant $\beta_1$.Furthermore, it is shown that at order $p^4$ the form factor F of the $K^0$does not show any off-shell dependence. The form factors G are all related tothe form factors F in the correct fashion as required by the Ward-Takahashiidentity. Numerical results for different off-shell kinematics are presented.Comment: TRIUMF preprint TRI-PP-94-4, 25 pages in LaTeX + 10 figures  (uufile'd, compressed PostScript file appended at end, hardcopy available  from authors

Off-shell electromagnetic form factors of pions and kaons in chiral perturbation theory