  The pion mass dependence of hyperon electromagnetic properties is determined
using two-flavor heavy baryon chiral perturbation theory. Specifically we
compute chiral corrections to the charge radii, magnetic moments, and magnetic
radii of the spin one-half hyperons, as well as the charge radii, magnetic
moments, magnetic radii, electric quadrupole moments, and quadrupole radii of
the spin three-half hyperons. Results for the nucleon and delta are also
included. Efficacy of the two-flavor theory is investigated by analyzing the
role played by virtual kaons. For the electromagnetic properties of spin
one-half hyperons, kaon loop contributions are shown to be well described by
terms analytic in the pion mass squared. Similarly kaon contributions to the
magnetic moments of spin three-half hyperons are well described in the
two-flavor theory. The remaining electromagnetic properties of spin three-half
resonances can be described in two-flavor chiral perturbation theory, however,
this description fails just beyond the physical pion mass. For the case of
experimentally known hyperon magnetic moments and charge radii, we demonstrate
that chiral corrections are under reasonable control, in contrast to the
behavior of these observables in the three-flavor chiral expansion. The
formulae we derive are ideal for performing the pion mass extrapolation of
lattice QCD data obtained at the physical strange quark mass.
