Microlocal partition of energy for linear wave or Schrödinger equations

Abstract

We prove a microlocal partition of energy for solutions to linear half-wave or Schrödinger equations in any space dimension. This extends well-known (local) results valid for the wave equation outside the wave cone, and allows us in particular, in the case of even dimension, to generalize the radial estimates due to Côte, Kenig and Schlag to non radial initial data. 0 Introduction The goal of this paper is to revisit the property of space partition of energy when time goes to infinity for solutions of linear wave equations that has been uncovered by Duyckaerts, Kenig and Merle [6, 7] in odd dimensions and by Côte, Kenig and Schlag [4] in even dimensions, and to extend it to other dispersive equations. Recall that if w solves the linear wave equation on R× Rd (∂ t −∆x)w = 0 w|t=0 = w0 ∂tw|t=0 = w1 and if one defines the energy at time t outside the wave cone by (1) E(w0, w1, t) = ∫ |x|>|t| [ |∂tw(t, x)| + |∇xw(t, x)| ] dx, then it has been proved in [6, 7] that, if d is odd, either ∀t ≥ 0, E(w0, w1, t) ≥ 1 2 [ ‖w1‖L2 + ‖∇xw0‖ 2 L2 ] or ∀t ≤ 0, E(w0, w1, t) ≥ 1 2 [ ‖w1‖L2 + ‖∇xw0‖ 2 L2 ] . (2) 2020 Mathematics Subject Classification: 35L05, 35Q41.