Relativistic Aharonov-Casher phase in spin 1

The Aharonov-Casher (AC) phase is calculated in relativistic wave equations of spin 1. The AC phase has previously been calculated from the Dirac-Paul i equation using a gauge-like technique. In the spin-1 case, we use Kemmer theory (a Dirac-like particle theory) to calculate the phase in a similar m anner. However, the vector formalism, the Proca theory, is more widely know n and used. In the presence of an electromagnetic field, the two theories a re 'equivalent' and may be transformed into one another. We adapt these tra nsformations to show that the Kemmer theory results apply to the Proca theo ry. Then we calculate the Aharonov-Casher phase for spin-1 particles direct ly in the Proca formalism.