  Using dispersion theory, the electromagnetic Sigma-to-Lambda transition form
factors are expressed as the product of the pion electromagnetic form factor
and the $\Sigma\bar{\Lambda}\to\pi\pi$ scattering amplitudes with the latter
estimated from SU(3) chiral perturbation theory including the baryon decuplet
as explicit degrees of freedom. The contribution of the $K\bar{K}$ channel is
also taken into account and the $\pi\pi$-$K\bar{K}$ coupled-channel effect is
included by means of a two-channel Muskhelishvili-Omn\`{e}s representation. It
is found that the electric transition form factor shows a significant shift
after the inclusion of the $K\bar{K}$ channel, while the magnetic transition
form factor is only weakly affected. However, the $K\bar{K}$ effect on the
electric form factor is obscured by the undetermined coupling $h_A$ in the
three-flavor chiral Lagrangian. The error bands of the Sigma-to-Lambda
transition form factors from the uncertainties of the couplings and low-energy
constant in three-flavor chiral perturbation theory are estimated by a
bootstrap sampling method.
