Improved time-decay for a class of scaling critical electromagnetic Schrodinger flows

We consider a Schrodinger hamiltonian $H(A,a)$ with scaling critical and time independent external electromagnetic potential, and assume that the angular operator $L$ associated to $H$ is positive definite. We prove the following: if $|e^{-itH(A,a)}|_{L^1to L^infty}lesssim t^{-n/2}$, then $ ||x|^{-g(n)}e^{-itH(A,a)}|x|^{-g(n)}|_{L^1to L^infty}lesssim t^{-n/2-g(n)}$, $g(n)$ being a positive number, explicitly depending on the ground level of $L$ and the space dimension $n$. We prove similar results also for the heat semi-group generated by $H(A,a)$.