Energy decay laws in strongly anisotropic MHD turbulence

We investigate the influence of a uniform magnetic field ${\bf B_0}=B_0 e//$ on energy decay laws in incompressible magnetohydrodynamic (MHD) turbulence. The nonlinear transfer reduction along $B_0$ is included in a model that distinguishes parallel and perpendicular directions, following a phenomenology {\it \`a la} Kraichnan. We predict a slowing down of the energy decay due to anisotropy in the limit of strong $B_0$, with distinct power laws for energy decay of shear- and pseudo-Alfv\'en waves. Numerical results from the kinetic equations of Alfv\'en wave turbulence recover these predictions, and MHD numerical results clearly tend to follow them in the lowest perpendicular planes.