Fiscal policy, debt constraint and expectations-driven volatility
用Ramsey模型证明，将公共债务与GDP之比设为常数这一约束，反而可能成为预期驱动波动的根源，因为政府跨期预算约束使所得税负依赖于未来债务和预期产出，导致预期自我实现。
Imposing some constraints on public debt is often justified regarding sustainability and stability issues. This is especially the case when the ratio of public debt over GDP is restricted to be constant. Using a Ramsey model, we show that such a constraint can however be a fundamental source of indeterminacy, and therefore, of expectations-driven fluctuations. Indeed, through the intertemporal budget constraint of the government, income taxation negatively depends on future debt, i.e. on the expected level of production. This mechanism ensures that expectations on the future tax rate may be self-fulfilling. We show that this is promoted by a larger ratio of debt over GDP.