We consider semiclassical scattering for compactly supported perturbations of the Laplacian and show equidistribution of eigenvalues of the scattering matrix at (classically) non-degenerate energy levels. The only requirement is that sets of fixed points of certain natural scattering relations have measure zero. This extends the result of [GRHZ15], where the authors proved the equidistribution result under a similar assumption on fixed points but with the condition that there is no trapping.
IntroductionConsider a Riemannian manifold (X, g) which is Euclidean near infinity, in the sense that there exist compact sets X 0 ⊂ X and K 0 ⊂ R d such that (X\X 0 , g) and (R d \K 0 , g eucl ) are isometric.Let us consider an operatorWe define the scattering matrix 1 S h : C ∞ (S d−1 ) −→ C ∞ (S d−1 ), which depends on h, by S h (φ in ) := e iπ(d−1)/2 φ out .The factor e iπ(d−1)/2 is taken so that the scattering matrix is the identity operator when (X, g) = (R d , g Eucl ) and V ≡ 0.For each h ∈ (0, 1], S h can be extended by density to a unitary operator acting on L 2 (S d−1 ). S h − Id is then a trace class operator. Therefore, S h admits a sequence of eigenvalues of modulus 1, which converge to 1, and which we denote by (e iβ h,n ) n∈N .Our aim in this paper will be to study the behaviour of (e iβ h,n ) in the limit where h → 0. To do this, we define a measure µ h on S 1 byfor any continuous f : S 1 −→ C. This measure is not finite, but µ h , f is finite as soon as 1 is not in the support of f .Let us now state the assumptions we make on the manifold X and on the potential V .