This paper studies how the impact of monetary policy depends on the distribution of savings from refinancing mortgages. We show that the efficacy of monetary policy is state dependent, varying in a systematic way with the pool of potential savings from refinancing. We construct a quantitative dynamic life-cycle model that accounts for our findings and use it to study how the response of consumption to a change in mortgage rates depends on the distribution of savings from refinancing. These effects are strongly state dependent. We also use the model to study the impact of a long period of low interest rates on the potency of monetary policy. We find that this potency is substantially reduced both during the period and for a substantial amount of time after interest rates renormalize.

We propose a model of sovereign debt in which countries vary in their level of financial development, defined as the extent to which they can issue debt denominated in domestic currency in international capital markets. We show that low levels of financial development generate the “debt intolerance” phenomenon that plagues emerging markets: it reduces overall debt capacity, increases credit spreads, and limits the country's ability to smooth consumption.

Using a quantitative model that features technical progress in automation and endogenous skill choice, we show that, given the current U.S. tax system, a sustained fall in automation costs can lead to a massive rise in income inequality. We characterize the optimal tax system in this model. We find that it is optimal to tax robots while the current generations of routine workers, who can no longer move to non-routine occupations, are active in the labour force. Once these workers retire, optimal robot taxes are zero.