Decay of solutions of diffusive Oldroyd-B system in ${\mathbb{R}}^2$

We show that strong solutions of 2D diffusive Oldroyd-B systems in ${\mathbb{R}}^2$ decay at an algebraic rate, for a large class of initial data. The main ingredient for the proof is the following fact; an Oldroyd-B system is a macroscopic closure of a Fokker-Planck-Navier-Stokes system, and the free energy of this Fokker-Planck-Navier-Stokes system decays over time. In particular, $\text{norm}{u}_{L_t^{\mathrm{\infty }}{L}_x^2}$ and $\norm{\nabla_x u}_{L^2_t L^2_x }$ are uniformly bounded for all time.