Kovtun, A.Nugaev, E.Shkerin, A.2018-12-132018-12-132018-12-132018-11-2710.1103/PhysRevD.98.096016https://infoscience.epfl.ch/handle/20.500.14299/152574WOS:000451591200010We study linear perturbations of classically stable Q-balls in theories admitting analytic solutions. Although the corresponding boundary value problem is non-Hermitian, the analysis of perturbations can also be performed analytically in certain regimes. We show that in theories with the flat potential, large Q-balls possess soft excitations. We also find a specific vibrational mode for Q-balls with a near-critical charge, where the perturbation theory for excitations can be developed. Comparing with the results on stability of Q-balls provides additional checks of our analysis.Astronomy & AstrophysicsPhysics, Particles & FieldsPhysicstext::journal::journal article::research article