We extend calculational techniques for static solitons to the case of field
configurations with simple time dependence in order to consider quantum ef
fects on the stability of Q-balls. These non-topological solitons exist cla
ssically for any fixed value of an unbroken global charge Q. We show that o
ne-loop quantum effects can destabilize very small Q-balls. We show how the
properties of the soliton are reflected in the associated scattering probl
em, and find that a good approximation to the full one-loop quantum energy
of a Q-ball is given by omega - E-0, where omega is the frequency of the cl
assical soliton's time dependence, and E-0 is the energy of the lowest boun
d state in the associated scattering problem. (C) 2001 Elsevier Science B.V
. All rights reserved.