Concurrence à la Cournot, accumulation du capital et bulle

This paper investigates the macroeconomic portfolio implications of monopoly rents. We make use of a two-sectors overlapping generations model with a Cournot oligopoly in one sector. We show that when the competitive equilibrium is characterized by under-capitalization with respect to the golden rule, an increase in the number of firms in the oligopoly leads to a decrease in profits, an increase in capital and life-cycle utility at steady-state. When the number of firms increases without limits, the steady-state equilibrium tends to the competitive equilibrium. When the competitive equilibrium is characterized by over-capitalization with respect to the golden rule, an increase in the number of firms in the oligopoly results in a decrease in profits and in the life-cycle utility, and an increase in capital. The life-cycle utility of agents is strictly greater than the one they get at the competitive equilibrium. Under the above assumption, the value of claims on firms in the oligopoly does not tend to zero when their number tends to infinity. There is a bubble on the claims on firms and the limit of the steady-state equilibrium is not the competitive equilibrium but the Allais-Diamond-Samuelson optimum. In the limit, the capital reaches its golden rule level. We thus have shown that claims on oligopolistic firms are another asset (different from land, public debt, pay-as-you-go pensions systems, Tiroles's bubbles) which prevents an economy from over-accumulating.