Q-balls and the proton stability in supersymmetric theories

Abelian non-topological solitons with Baryon and/or Lepton quantum numbers naturally appear in the spectrum of the minimal supersymmetric standard mod el. They arise as a consequence of the existence of flat directions in the potential Lifted by nan-renormalizable operators and SUSY breaking. We exam ine the conditions that these operators should satisfy in order to ensure p roton stability and present a realistic string model which fulfills these r equirements. We further identify a generic U(1) breaking term in the scaler potential and discuss its effect of rendering Q-balls unstable. (C) 1999 E lsevier Science B.V. All rights reserved.