Problem with classical stability of U(1) gauged Q-balls

In this paper, we present a detailed study of the problem of classical stability of U(1) gauged Q-balls. In particular, we show that the standard methods that are suitable for establishing the classical stability criterion for ordinary (nongauged) one-field and two-field Q-balls are not effective in the case of U(1) gauged Q-balls, although all the technical steps of calculations can be performed in the same way as those for ordinary Q-balls. We also present the results of numerical simulations in models with different scalar field potentials, explicitly demonstrating that, in general, the regions of stability of U(1) gauged Q-balls are not defined in the same way as in the case of ordinary Q-balls. Consequently, the classical stability criterion for ordinary Q-balls cannot be applied to U(1) gauged Q-balls in the general case.