“…Existence and non-existence results, under different assumptions on the nonlinearity and on m and ω are present in [1,10,11], while the existence of a ground state has been considered in [2,30]. Moreover we mention [13,14], for the bounded domain case, and [9,15,17,19,20], for the case A = 0 and µ = 0 on manifolds. Finally Klein-Gordon equations coupled with Born-Infeld type equations have been treated in [8,12,32].…”