Rational bubbles in non-linear business cycle models: Closed and open economies

This paper studies rational bubbles in non-linear dynamic general equilibrium models of the macroeconomy. The term ‘Rational bubble’ refers to multiple equilibria due to the absence of a transversality condition (TVC) for capital. The lack of TVC can be due to an OLG population structure. If a TVC is imposed, the macro models considered here have a unique solution. Bubbles reflect self-fulfilling fluctuations in agents’ expectations about future investment. In contrast to explosive rational bubbles in linearized models (Blanchard (1979)), the rational bubbles in non-linear models here are bounded. Bounded rational bubbles provide a novel perspective on the drivers and mechanisms of business cycles. I construct bubbles (in non-linear models) that feature recurrent boombust cycles characterized by persistent investment and output expansions which are followed by abrupt contractions in real activity. Both closed and open economies are analyzed. In a non-linear two-country model with integrated financial markets, bubbles must be perfectly correlated across countries. Global bubbles may, thus, help to explain the synchronization of international business cycles.