  For a stochastic factor model we maximize the long-term growth rate of robust
expected power utility with parameter $\lambda\in(0,1)$. Using duality methods
the problem is reformulated as an infinite time horizon, risk-sensitive control
problem. Our results characterize the optimal growth rate, an optimal long-term
trading strategy and an asymptotic worst-case model in terms of an ergodic
Bellman equation. With these results we propose a duality approach to a "robust
large deviations" criterion for optimal long-term investment.
