We introduce a portfolio friction in a two-country DSGE model where investors face a constant probability to make new portfolio decisions. The friction leads to a more gradual portfolio adjustment to shocks and a weaker portfolio response to changes in expected excess returns. We apply the model to monthly data for the US and the rest of the world for equity portfolios. We show that the model is consistent with a broad set of evidence related to portfolios, equity prices, and excess returns for an intermediate level of friction. The evidence includes portfolio inertia, limited sensitivity to expected excess returns, a significant impact of financial shocks, excess return predictability, and asset price momentum and reversal.

Recent crises have seen large spikes in asset price risk. We propose an explanation for such panics based on self-fulfilling shifts in beliefs about risk. A negative link between the current level and the future risk of an asset price leads to a circular relationship between the stochastic process of asset price risk and the price itself. Self-fulfilling shifts in perceived risk can be coordinated around a pure sunspot or around a macro fundamental. In a risk panic, a macro fundamental can be a focal point that affects both the magnitude of the panic and subsequent shifts in perceived risk.

There has been a long debate about whether speculators are stabilizing or not. We consider a model where speculators have a stabilizing role in normal times, but may also provoke large risk panics. The very feature that makes arbitrageurs liquidity providers in normal times, namely their tolerance of risk, enables a large increase in asset price risk during a financial panic. We show that a policy that discourages balance sheet risk reduces the magnitude of financial panics, as well as asset price risk in both normal and panic states.