NONEQUILIBRIUM PHENOMENA IN GLOBALLY COUPLED ACTIVE ROTATORS WITH MULTIPLICATIVE AND ADDITIVE NOISES

We investigate noise-induced phase transitions in globally coupled act ive rotators with multiplicative and additive noises. In the system th ere are four phases, stationary one-cluster, stationary two-cluster, m oving one-cluster, and moving two-cluster phases. It is shown that mul tiplicative noise induces a bifurcation from one-cluster phase to two- cluster phase. Pinning force also induces a bifurcation from moving ph ase to stationary phase suppressing the multiplicative noise effect. A dditive noise reduces both effects of multiplicative noise and pinning force urging the system to the stationary one-cluster phase. The frus trated effects of pinning force and additive and multiplicative noises lead to a reentrant transition at intermediate additive noise intensi ty. Nature of the transition is also discussed.