  Lucas and Moll have proposed a system of forward-backward partial
differential equations that model knowledge diffusion and economic growth. It
arises from a microscopic model of learning for a mean-field type interacting
system of individual agents. In this paper, we prove existence of traveling
wave solutions to this system. They correspond to what is known in economics as
balanced growth path solutions. We also study the dependence of the solutions
and their propagation speed on various economic parameters of the system.
