The theory contains Q-ball solutions if there are any values of formula_19 at which the potential is less than formula_20. In this case, a volume of space with the field at that value can have an energy per unit charge that is less than formula_21, meaning that it cannot decay into a gas of individual particles. Such a region is a Q-ball. If it is large enough, its interior is uniform, and is called "Q-matter". (For a review see Lee "et al." (1992).