Mean field game (MFG) systems describe equilibrium configurations in games with
infinitely many interacting controllers. We are interested in the behavior of
this system as the horizon becomes large, or as the discount factor tends to
. We
show that, in these two cases, the asymptotic behavior of the mean field game system
is strongly related to the long time behavior of the so-called master equation and to
the vanishing discount limit of the discounted master equation, respectively. Both
equations are nonlinear transport equations in the space of measures. We prove the
existence of a solution to an ergodic master equation, towards which the
time-dependent master equation converges as the horizon becomes large, and towards
which the discounted master equation converges as the discount factor tends to
. The
whole analysis is based on new estimates for the exponential rates of convergence of
the time-dependent and the discounted MFG systems, respectively.
Keywords
mean field games, weak KAM theory, long time behavior