Non-Algebraic Decay for Solutions to the Navier-Stokes Equations

Around forty years ago, Michael Wiegner provided, in a seminal paper, sharp algebraic decay rates for solutions of the Navier–Stokes equations, showing that these solutions behave asymptotically like the solutions of the heat equation with the same data as $t\to +\mathrm{\infty }$, in the $L^2$-norm, up to some critical decay rate. In the present paper, we close a gap that appears in the conclusion of Wiegner’s theorem in the 2D case, for solutions with non-algebraic decay rate.