Asset Prices and Aggregate Demand in a "Covid-19" Shock: A Model of Endogenous Risk Intolerance and LSAPs

In this paper we: (i) provide a model of the endogenous risk intolerance and severe aggregate demand contractions following a large real (non-financial) shock; and (ii) demonstrate the effectiveness of Large Scale Asset Purchases (LSAPs) in addressing these contractions. The key mechanism stems from heterogeneous risk tolerance: as a recessionary shock hits the economy and brings down asset prices, risk-tolerant agents' wealth share declines and their leverage rises endogenously. This reduces the market's risk tolerance and generates downward pressure on asset prices and aggregate demand. When monetary policy is unconstrained, it can offset the decline in risk tolerance with an interest rate cut that boosts the market's Sharpe ratio. However, if the interest rate policy is constrained, new contractionary feedbacks arise: recessionary shocks lead to further asset price and output drops, which feed the risk-off episode and trigger a downward loop. In this context, LSAPs improve asset prices and aggregate demand by transferring risk to the government's balance sheet, which reduces the market's required Sharpe ratio. Optimal LSAPs are larger when the (consolidated) government has greater future fiscal capacity and the downward spiral is more severe. In an extension, we show how corporate debt overhang problems strengthen our mechanisms. The Covid-19 shock and the large response by all the major central banks provide a vivid illustration of the environment we seek to capture.