Wave front set

Abstract: There are many approaches to conventional Euclidian scattering theory. In this exposition an essentially microlocal view is adopted. Apart from its intrinsic interest this is intended as preparation for later generalization, to more complicated geometric settings. In fact, the treatment given here extends beyond the usual confines of scattering theory in that the spectral and scattering theory, at least the elementary part, is covered for the Laplacian associated to a ‘scattering metric’ on any compact manifold with boundary.

Abstract: I. Test Functions.- Summary.- 1.1. A review of Differential Calculus.- 1.2. Existence of Test Functions.- 1.3. Convolution.- 1.4. Cutoff Functions and Partitions of Unity.- Notes.- II. Definition and Basic Properties of Distributions.- Summary.- 2.1. Basic Definitions.- 2.2. Localization.- 2.3. Distributions with Compact Support.- Notes.- III. Differentiation and Multiplication by Functions.- Summary.- 3.1. Definition and Examples.- 3.2. Homogeneous Distributions.- 3.3. Some Fundamental Solutions.- 3.4. Evaluation of Some Integrals.- Notes.- IV. Convolution.- Summary.- 4.1. Convolution with a Smooth Function.- 4.2. Convolution of Distributions.- 4.3. The Theorem of Supports.- 4.4. The Role of Fundamental Solutions.- 4.5. Basic Lp Estimates for Convolutions.- Notes.- V. Distributions in Product Spaces.- Summary.- 5.1. Tensor Products.- 5.2. The Kernel Theorem.- Notes.- VI. Composition with Smooth Maps.- Summary.- 6.1. Definitions.- 6.2. Some Fundamental Solutions.- 6.3. Distributions on a Manifold.- 6.4. The Tangent and Cotangent Bundles.- Notes.- VII. The Fourier Transformation.- Summary.- 7.1. The Fourier Transformation in ? and in ?'.- 7.2. Poisson's Summation Formula and Periodic Distributions.- 7.3. The Fourier-Laplace Transformation in ?'.- 7.4. More General Fourier-Laplace Transforms.- 7.5. The Malgrange Preparation Theorem.- 7.6. Fourier Transforms of Gaussian Functions.- 7.7. The Method of Stationary Phase.- 7.8. Oscillatory Integrals.- 7.9. H(s), Lp and Holder Estimates.- Notes.- VIII. Spectral Analysis of Singularities.- Summary.- 8.1. The Wave Front Set.- 8.2. A Review of Operations with Distributions.- 8.3. The Wave Front Set of Solutions of Partial Differential Equations.- 8.4. The Wave Front Set with Respect to CL.- 8.5. Rules of Computation for WFL.- 8.6. WFL for Solutions of Partial Differential Equations.- 8.7. Microhyperbolicity.- Notes.- IX. Hyperfunctions.- Summary.- 9.1. Analytic Functionals.- 9.2. General Hyperfunctions.- 9.3. The Analytic Wave Front Set of a Hyperfunction.- 9.4. The Analytic Cauchy Problem.- 9.5. Hyperfunction Solutions of Partial Differential Equations.- 9.6. The Analytic Wave Front Set and the Support.- Notes.- Exercises.- Answers and Hints to All the Exercises.- Index of Notation.

Abstract: We define the Gabor wave front set $$WF_G(u)$$ of a tempered distribution $$u$$ in terms of rapid decay of its Gabor coefficients in a conic subset of the phase space We show the inclusion $$\begin{aligned} WF_G(a^w(x,D) u)\subseteq WF_G(u), \quad u \in \fancyscript{S}'({\mathbb {R}}^{d}),\ a \in S_{0,0}^0, \end{aligned}$$ where $$S_{0,0}^0$$ denotes the Hormander symbol class of order zero and parameter values zero We compare our definition with other definitions in the literature, namely the classical and the global wave front sets of Hormander, and the $$\fancyscript{S}$$ -wave front set of Coriasco and Maniccia In particular, we prove that the Gabor wave front set and the global wave front set of Hormander coincide