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Andras Vasy

Publications and source records attributed to Andras Vasy.

49 records · Page 3Linked to original sources
arXiv2002

Complex powers and non-compact manifolds

We study the complex powers $A^{z}$ of an elliptic, strictly positive pseudodifferential operator $A$ using an axiomatic method that combines the approaches of Guillemin and Seeley. In particular, we introduce a class of algebras, ``extended Weyl algebras,'' whose definition was inspired by Guillemin's paper on the subject. An extended Weyl algebra can be thought of as an algebra of ``abstract pseudodifferential operators.'' Many algebras of pseudodifferential operators are extended Weyl algebras. Several results typical for algebras of pseudodifferential operators (asymptotic completeness, construction of Sobolev spaces, boundedness between apropriate Sobolev spaces, >...) generalize to extended Weyl algebras. Most important, our results may be used to obtain precise estimates at infinity for $A^{z}$, when $A > 0 $ is elliptic and defined on a non-compact manifold, provided that a suitable ideal of regularizing operators is specified (a submultiplicative $Ψ^*$--algebra). We shall use these results in a forthcoming paper to study pseudodifferential operators and Sobolev spaces on manifolds with a Lie structure at infinity (a certain class of non-compact manifolds).

math.OA↗
arXiv2002

Geometry and analysis in many-body scattering

These are my lecture notes from a minicourse I gave at the Universite de Nantes about many-body scattering. I also discuss the relationship between many-body scattering and higher rank symmetric spaces, whose description is the result of joint work with Rafe Mazzeo.

math.AP↗
arXiv2002

Analytic continuation of the resolvent of the Laplacian on SL(3)/SO(3)

In this paper we continue our program of extending the methods of geometric scattering theory to encompass the analysis of the Laplacian on symmetric spaces of rank greater than one and their geometric perturbations. In our previous work we described the resolvent, and specifically the asymptotic behavior of the Green's function, on SL(3)/SO(3) using methods from three-particle scattering. Here we extend the technique of complex scaling to symmetric spaces to show that the resolvent continues analytically across the spectrum.

math.AP↗
arXiv2001

Low energy inverse problems in three-body scattering

We consider low energy inverse problems in three-body scattering and show that if all unknown interactions are small in an appropriate sense then the 2-cluster to 2-cluster S-matrices given at low energies determine the Fourier transform of the effective interaction in a ball.

math.AP↗
arXiv2001

Smoothness and high energy asymptotics of the spectral shift function in many-body scattering

Let H=Δ+\sum_{#a=2} V_a be a 3-body Hamiltonian, H_a the subsystem Hamiltonians, Δthe positive Laplacian of the Euclidean metric on X_0=R^n, V_a real-valued. Buslaev and Merkurev have shown that, if the pair potentials decay sufficiently fast, for ϕsmooth and compactly supported, the operator ϕ(H)-ϕ(H_0)-\sum_{#a=2}(ϕ(H_a)-ϕ(H_0)) is trace class. Hence, one can define a modified spectral shift function σ, as a distribution on R, by taking its trace. In this paper we show that if V_a are Schwartz, then σis in fact smooth away from the thresholds, and obtain its high energy asymptotics. In addition, we generalize this result to N-body scattering, N arbitrary.

math.AP↗
arXiv2000

Intersecting Legendrians and blowups

The purpose of this note is to describe the relationship between two classes of Legendre distributions. These two classes are distributions associated to an intersecting pair of Legendre submanifolds, introduced by one of us by analogy with intersecting Lagrangian distributions of Melrose and Uhlmann, and Legendre distributions associated to a fibred scattering structure introduced by the authors. We prove a general result, and also give an example in two dimensions, which shows explicitly the relation between the two spaces in a simple setting.

math.AP↗
arXiv2000

Resolvents and Martin boundaries of product spaces

In this paper we examine the Laplacian on the product of two asymptotically hyperbolic (or conformally compact, as they are often called) spaces from the point of view of geometric scattering theory. In particular, we describe the asymptotic behavior of the resolvent applied to Schwartz functions and that of the resolvent kernel itself. We use these results to find the Martin boundary of the product space. This behaves (nearly) as expected when the factors have no $L^2$ eigenvalues, but it experiences a substantial collapse in the presence of such eigenvalues.

math.DG↗
arXiv2000

The resolvent for Laplace-type operators on asymptotically conic spaces

Let X be a compact manifold with boundary, and g a scattering metric on X, which may be either of short range or `gravitational' long range type. Thus, g gives X the geometric structure of a complete manifold with an asymptotically conic end. Let H be an operator of the form $H = Δ+ P$, where $Δ$ is the Laplacian with respect to g and P is a self-adjoint first order scattering differential operator with coefficients vanishing at the boundary of X and satisfying a `gravitational' condition. We define a symbol calculus for Legendre distributions on manifolds with codimension two corners and use it to give a direct construction of the resolvent kernel of H, $R(σ+ i0)$, for $σ$ on the positive real axis. In this approach, we do not use the limiting absorption principle at any stage; instead we construct a parametrix which solves the resolvent equation up to a compact error term and then use Fredholm theory to remove the error term.

math.AP↗
arXiv1999

Semiclassical estimates in asymptotically Euclidean scattering

In this note we obtain semiclassical resolvent estimates for non-trapping long range perturbations of the Laplacian on asymptotically Euclidean manifolds. Our proof is based on a positive commutator argument which differs from Mourre-type estimates by making the commutant also positive. The resolvent estimates, including the weighting of the Sobolev spaces in the estimates, are an immediate consequence.

math.AP↗
arXiv1999

Propagation of singularities in many-body scattering in the presence of bound states

We describe the propagation of singularities of tempered distributional generalized eigenfunctions of many-body Hamiltonians at non-threshold energies under the assumption that the inter-particle interactions are real-valued polyhomogeneous symbols of order -1 (e.g. Coulomb-type, but without the singularity at the origin). Here the term `singularity' refers to a microlocal description of the lack of decay at infinity. We use this result to describe the wave front relation of the S-matrices. We also analyze Lagrangian properties of this relation, which shows that the relation is not `too large' in terms of its dimension.

math.AP↗
arXiv1999

The spectral projections and the resolvent for scattering metrics

In this paper we consider certain asymptotically Euclidean spaces, namely compact manifolds with boundary X equipped with a scattering metric g, as defined by Melrose. We then consider Hamiltonians H which are `short-range' self-adjoint perturbations of the Laplacian of g. Melrose and Zworski have given a detailed description of the associated scattering matrix and Poisson operator as a Fourier integral operator and a (singular) Legendre distribution respectively. In this paper we describe the kernel of the spectral projections and the boundary value of the resolvent at the real axis. We define classes of Legendre distributions on certain types of manifolds with corners, and show that the kernels of the spectral projection and the resolvent are in these classes. We also discuss some applications of these results.

math.AP↗
arXiv1999

Propagation of singularities in many-body scattering

In this paper we describe the propagation of singularities of tempered distributional generalized eigenfunctions of many-body Hamiltonians under the assumption that no subsystem has a bound state and that the two-body interactions are real-valued polyhomogeneous symbols of order -1 (e.g. Coulomb-type with the singularity at the origin removed). Here the term 'singularity' provides a microlocal description of the lack of decay at infinity. We use this result to prove that the wave front relation of the free-to-free S-matrix (which, under our assumptions, is all of the S-matrix) is given by the broken geodesic relation, broken at the 'singular directions' (given by the collision planes) on the sphere, at time pi. We also present a natural geometric generalization to asymptotically Euclidean spaces.

math.AP↗