On the existence of stable charged Q-balls

This paper concerns hylomorphic solitons, namely stable, solitary waves whose existence is related to the ratio energy/charge. In theoretical physics, the name Q-ball refers to a type of hylomorphic solitons or soli- tary waves relative to the Nonlinear Klein-Gordon equation (NKG). We are interested in the existence of charged Q-balls, namely Q-balls for the Nonlinear Klein-Gordon equation coupled with the Maxwell equations (NKGM). In this case the charge reduces to the electric charge. The main result of this paper establishes that stable, charged Q-balls exist provided that the interaction between matter and the gauge field is sufficiently small.