A Goldilocks Theory of Fiscal Deficits
构建了一个分析赤字与债务动态的框架，发现只有在特定条件下“免费午餐”赤字才可持续，并探讨了零利率下限和收入不平等对财政空间的影响，通过校准模型比较了美国和日本的情况。
We develop a tractable framework for deficit and debt dynamics. A “free lunch” fiscal deficit—one that raises spending without higher future taxes—is sustainable without zero lower bound (ZLB) only when R < G − φ, where φ is the sensitivity of the interest rate to the debt level. With the ZLB, both high and low deficits can increase debt, as the latter weaken demand and reduce nominal growth at the ZLB. A rise in income inequality expands fiscal space outside the ZLB, but contracts it at the ZLB. Calibrating the model, we find little space for “free lunch” policies for the United States in 2019, but significant space for Japan.