  Motivated by recent axiomatic developments, we study the risk- and
ambiguity-averse investment problem where trading takes place over a fixed
finite horizon and terminal payoffs are evaluated according to a criterion
defined in terms of a quasiconcave utility functional. We extend to the present
setting certain existence and duality results established for the so-called
variational preferences by Schied (2007). The results are proven by building on
existing results for the classical utility maximization problem.
