A. Niknam

[ 1 ] - Existence of ground states for approximately inner two--parameter $C_0$--groups on $C^*$--algebras

In this paper, we generalize the definitions of approximately inner $C_0$-groups and their ground states to the two- parameter case and study necessary and sufficient conditions for a state to be ground state. Also we prove that any approximately inner two- parameter $C_0$--group must have at least one ground state. Finally some applications are given.