Iranian Mathematical Society (IMS)Bulletin of the Iranian Mathematical Society1017-060X42220160401Existence of ground states for approximately inner two--parameter $C_0$--groups on $C^*$--algebras435446770ENR.AbazariDepartment of
Mathematics, Mashhad Branch, Islamic Azad University, Mashhad, Iran.A.NiknamDepartment of
Mathematics, Mashhad Branch, Islamic Azad University, Mashhad, Iran.Journal Article20131213In 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.http://bims.iranjournals.ir/article_770_d466d7717510eb9caf6af9b237000141.pdf