  Recent studies have shown that gamma-ray pulsar light curves are very
sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field
geometries, such as the retarded vacuum dipole and force-free magnetospheres
have distorted polar caps that are offset from the magnetic axis in the
direction opposite to rotation. Since this effect is due to the sweepback of
field lines near the light cylinder, offset polar caps are a generic property
of pulsar magnetospheres and their effects should be included in gamma-ray
pulsar light curve modeling. In slot gap models (having two-pole caustic
geometry), the offset polar caps cause a strong azimuthal asymmetry of the
particle acceleration around the magnetic axis. We have studied the effect of
the offset polar caps in both retarded vacuum dipole and force-free geometry on
the model high-energy pulse profiles. We find that, compared to the profiles
derived from symmetric caps, the flux in the pulse peaks, which are caustics
formed along the trailing magnetic field lines, increases significantly
relative to the off-peak emission, formed along leading field lines. The
enhanced contrast produces improved slot gap model fits to Fermi pulsar light
curves like Vela, with vacuum dipole fits being more favorable.
