Competition and regulation with product differentiation

We consider a market for differentiated products, where one good is supplied by a regulated monopolist and competitive firms operate in an unregulated segment. In this setting we investigate the issue of whether to allow the monopolist to diversify into the unregulated segment by owning a competitive firm. Under asymmetric cost information, if goods are substitutes a diversified monopolist, which exaggerates its costs in the regulated segment to charge a higher regulated price, stimulates the demand for the competitive affiliate. This strengthens the firm's incentive to inflate costs, since doing so generates a positive informational spillover to its profits in the competitive segment. Consequently, a regime of separation, which prevents the firm from operating in the competitive segment, is welfare-enhancing. Conversely, with complements, cost exaggeration in the regulated monopoly reduces the demand and harms profits in the competitive segment, and allowing the monopolist to diversify into the competitive segment therefore generates countervailing incentives, which weaken the firm's interest in cost manipulation and improve social welfare.