  The evolution of domain structure is investigated in a two-dimensional voter
model with three states under cyclic dominance. The study focus on the dynamics
of vortices, defined by the points where three states (domains) meet. We can
distinguish vortices and antivortices which walk randomly and annihilate each
other. The domain wall motion can create vortex-antivortex pairs at a rate
which is increased by the spiral formation due to the cyclic dominance. This
mechanism is contrasted with a branching annihilating random walk (BARW) in a
particle antiparticle system with density dependent pair creation rate.
Numerical estimates for the critical indices of the vortex density
($\beta=0.29(4)$) and of its fluctuation ($\gamma=0.34(6)$) improve an earlier
Monte Carlo study [Tainaka and Itoh, Europhys. Lett. 15, 399 (1991)] of the
three-state cyclic voter model in two dimensions.
