On Questions of Decay and Existence for the Viscous Camassa-Holm Equations

We consider the viscous $n$-dimensional Camassa-Holm equations, with $n=2,3,4$ in the whole space. We establish existence and regularity of the solutions and study the large time behavior of the solutions in several Sobolev spaces. We first show that if the data is only in $L^2$ then the solution decays without a rate and that this is the best that can be expected for data in $L^2$. For solutions with data in $H^m\cap L^1$ we obtain decay at an algebraic rate which is optimal in the sense that it coincides with the rate of the underlying linear part.