We consider portfolio selection under nonparametric alpha-maxmin ambiguity in the neighbourhood of a reference distribution. We show strict concavity of the portfolio problem under ambiguity aversion.Implied demand functions are nondifferentiable, resemble observed bid-ask spreads, and are...

We consider a linear factor APT model and assume that agents are ambiguity averse with respect to payoffs of arbitrage portfolios. In contrast to the standard result, pricing errors need not converge to zero in the limit as the number of assets goes to infinity. Even in the case of exact factor...