We propose a rational theory of momentum and reversal based on delegated portfolio management. A competitive investor can invest through an index fund or an active fund run by a manager with unknown ability. Following a negative cashflow shock to assets held by the active fund, the investor...

Kirman’s “ant model” has been used to characterize the expectation formation of financial investors who are prone to herding. The model’s original version suffers from the problem of N-dependence: its ability to replicate the statistical features of financial returns vanishes once the...