Modelling Alpha-Opportunities Within the CAPM∗

We consider a simple CAPM with heterogenous expectations on assets’ mean returns and homogenous expectations on the covariance of returns. In this model alpha-opportunities naturally arise in a financial market equilibrium. We show that that the hunt for alpha-opportunities is a zero-sum game and that alpha-opportunities erode with the assets under management. Moreover, it is shown that a positive alpha is not necessarily a good criterion for the choice between active and passive investment. Finally, we argue that the standard CAPM with homogenous beliefs can be seen as the long run outcome of our model when investors’ expectations are endogenous.