Optimal Monetary Policy and Rational Asset Bubbles

Using a New Keynesian model with stochastic asset market participation, we analyze the normative implications of bubbly fluctuations for monetary policy. We show that stochastic asset-market participation allows rational bubbles to emerge in equilibrium despite the fact that households are infinitely lived. A central bank concerned with social welfare faces an additional tradeoff implied by the effect of bubbly fluctuations on consumption dispersion across market participants, which makes, in general, strict inflation targeting a suboptimal monetary-policy regime. Deviations from inflation targeting are welfare improving in particular when the economy fluctuates around a balanced-growth path where equilibrium bubbles are small or absent, and the endogenous tradeoff is more stringent, requiring larger deviations of inflation/output gap to mitigate bubbly fluctuations in wealth and thus consumption inequality. The specific optimal monetary-policy response to bubbly fluctuations depends however on the intrinsic features of latter, and the associated effects on wealth inequality.