Pseudodifferential operators of Beurling type and the wave front set

We investigate the action of pseudodifferential operators of Beurling type on the wave front sets. More precisely, we show that these operators are microlocal, that is, preserve or reduce wave front sets. Some consequences on micro-hypoellipticity are derived.     

Wave Front Set at Infinity and Hyperbolic Linear Operators with Multiple Characteristics

We discuss a notion of wave front set which allows us tocontrol the behaviour `at infinity' of temperate distributions. Weobtain the microlocality and microellipticity properties with respect toa class of global pseudodifferential operators and a propagation theoremfor the corresponding class of Fourier Integral Operators. Through theseresults, we prove an adapted global version of the classical theoremconcerning the singularities of solutions of hyperbolic Cauchy problemsfor linear operators with multiple characteristics of constantmultiplicities. Finally, we make a comparison with the scattering wavefront set introduced by Melrose.     

Second analytic wave front set of the fundamental solutions of hyperbolic operators

The notion of a second microlocalization along an involutive submanifold WCIS introduced by M. Kashiwara [6] .Y. Laurent developed this notion and established a theory of the 2-microdifferential operators [8]. In [Ill, 3 . Sjostrand defined the second analytic wave front set (and even a kth wave front set) along the lagrangian submanifolds.So he was able to get a result of M. Kashiwara and to generalize it. This result provides very strict relations between the support and the wave front set, and, as a generalization, between the (k-l)th wave front set and the kth one. J.M.Bony gave a definition adapted to the frame of the C_∞o-singularities. Finally G. Lebeau spread the notion to the isotropic manifolds and applied it to a degenerated diffraction problem.     

Equality of the homogeneous and the Gabor wave front set

We prove that Hörmander’s global wave front set and Nakamura’s homogeneous wave front set of a tempered distribution coincide. In addition, we construct a tempered distribution with a given wave front set, and we develop a pseudodifferential calculus adapted to Nakamura’s homogeneous wave front set.     

Regularity of ghosts in tensor tomography

We study on a compact Riemannian manifold with boundary the ray transform I which integrates symmetric tensor fields over geodesics. A tensor field is said to be a nontrivial ghost if it is in the kernel of I and is L²-orthogonal to all potential fields. We prove that a nontrivial ghost is smooth in the case of a simple metric. This implies that the wave front set of the solenoidal part of a field f can be recovered from the ray transform If. We give an explicit procedure for recovering the wave front set.     

Centers and isochronous centers of a class of quasi-analytic switching systems

In this paper, we study the integrability and linearization of a class of quadratic quasi-analytic switching systems. We improve an existing method to compute the focus values and periodic constants of quasianalytic switching systems. In particular, with our method, we demonstrate that the dynamical behaviors of quasi-analytic switching systems are more complex than those of continuous quasi-analytic systems, by showing the existence of six and seven limit cycles in the neighborhood of the origin and infinity, respectively, in a quadratic quasi-analytic switching system. Moreover, explicit conditions are obtained for classifying the centers and isochronous centers of the system.     

Propagation of Gabor singularities for Schrödinger equations with quadratic Hamiltonians

We study propagation of the Gabor wave front set for a Schrödinger equation with a Hamiltonian that is the Weyl quantization of a quadratic form with nonnegative real part. We point out that the singular space associated with the quadratic form plays a crucial role for the understanding of this propagation. We show that the Gabor singularities of the solution to the equation for positive times are always contained in the singular space, and that they propagate in this set along the flow of the Hamilton vector field associated with the imaginary part of the quadratic form. As an application we obtain for the heat equation a sufficient condition on the Gabor wave front set of the initial datum tempered distribution that implies regularization to Schwartz regularity for positive times.     

Unbounded subnormal weighted shifts on directed trees

A new method of verifying the subnormality of unbounded Hilbert space operators based on an approximation technique is proposed. Diverse sufficient conditions for subnormality of unbounded weighted shifts on directed trees are established. An approach to this issue via consistent systems of probability measures is invented. The role played by determinate Stieltjes moment sequences is elucidated. Lambert’s characterization of subnormality of bounded operators is shown to be valid for unbounded weighted shifts on directed trees that have sufficiently many quasi-analytic vectors, which is a new phenomenon in this area.     

Wave front sets for ultradistribution solutions of linear partial differential operators with coefficients in non‐quasianalytic classes

We prove the following inclusion where WF_* denotes the non‐quasianalytic Beurling or Roumieu wave front set, Ω is an open subset of $\mathbb {R}^n$, P is a linear partial differential operator with suitable ultradifferentiable coefficients, and Σ is the characteristic set of P. The proof relies on some techniques developed in the study of pseudodifferential operators in the Beurling setting. Some applications are also investigated.     

Wave front set at infinity for tempered ultradistributions and hyperbolic equations

Abstract We study the propagation of singularities and the microlocal behaviour at infinity for the solution of the Cauchy problem associated to an SG-hyperbolic operator with one characteristic of constant multiplicity. We perform our analysis in the framework of tempered ultradistributions, cf. Introduction, using an appropriate notion of wave front set. Keywords: Wave front set at infinity, Tempered ultradistributions, Hyperbolic equations     

Propagation of Exponential Phase Space Singularities for Schrödinger Equations with Quadratic Hamiltonians

We study propagation of phase space singularities for the initial value Cauchy problem for a class of Schrödinger equations. The Hamiltonian is the Weyl quantization of a quadratic form whose real part is non-negative. The equations are studied in the framework of projective Gelfand–Shilov spaces and their distribution duals. The corresponding notion of singularities is called the Gelfand–Shilov wave front set and means the lack of exponential decay in open cones in phase space. Our main result shows that the propagation is determined by the singular space of the quadratic form, just as in the framework of the Schwartz space, where the notion of singularity is the Gabor wave front set.     

一类反应扩散方程波前解的存在性

本文讨论一类反应扩散方程满足各种条件的单调波前解及振荡波前解的存在性；得到了一系列保证波前解存在的充分条件。     

Microlocal properties for pseudodifferential operators of type 1,1

The author studies the action of a new selfadjoint algebra of pseudodifferential operators of type (1,1) on Sobolev wave front sets for distributions.     

Large deviations for a symmetric branching random walk on a multidimensional lattice

An important role in the theory of branching random walks is played by the problem of the spectrum of a bounded symmetric operator, the generator of a random walk on a multidimensional integer lattice, with a one-point potential. We consider operators with potentials of a more general form that take nonzero values on a finite set of points of the integer lattice. The resolvent analysis of such operators has allowed us to study branching random walks with large deviations. We prove limit theorems on the asymptotic behavior of the Green function of transition probabilities. Special attention is paid to the case when the spectrum of the evolution operator of the mean numbers of particles contains a single eigenvalue. The results obtained extend the earlier studies in this field in such directions as the concept of a reaction front and the structure of a population inside a front and near its boundary.     

SINGULAR DIRECTIONS OF WF(u)AND ITS APPLICATION

This paper introduces the notion of the singular direction of wave front sets fordistributions and proves the invariance of the singular direction under the ellipticequivalent transformation.A kind of Fourier integral operators,which ensure suchinvariance,are also investigated.The results obtained are applied to the propagation ofsingularities for a class of differential operators with multiple characteristics.     

Quasi-analytic solutions of linear parabolic equations

Uniqueness of solutions of the Cauchy problem of a parabolic equation, and the related question of analyticity with respect to time, depend on global properties of the solution. We demonstrate that if the growth of the initial function (and, if relevant, of the inhomogeneous part and its derivatives) is not too great, solutions of non-stationary parabolic equations whose coefficients belong to quasi-analytic classes are quasi-analytic with respect to all variables and hence are unique. This study is motivated by the problem of endogenous completeness in continuous-time financial markets.     

Scattering of a High-Frequency Wave by the Vertex of an Arbitrary Cone (Singular Directions)

A new approach to the derivation of an analytic expression for the wave scattered in singular directions on the vertex of an arbitrary cone is developed. In such directions, the spherical front set of the wave scattered by the vertex is tangent to the front set of the wave reflected from the surface of the cone. The wave field is expressed in terms of functions of a parabolic cylinder. Bibliography: 10 titles.     

Microlocal Analysis of Generalized Pullbacks of?Colombeau Functions

In distribution theory the pullback of a general distribution by a C ^∞-function is well-defined whenever the normal bundle of the C ^∞-function does not intersect the wave front set of the distribution. However, the Colombeau theory of generalized functions allows for a pullback by an arbitrary c-bounded generalized function. It has been shown in previous work that in the case of multiplication of Colombeau functions (which is a special case of a C ^∞ pullback), the generalized wave front set of the product satisfies the same inclusion relation as in the distributional case, if the factors have their wave front sets in favorable position. We prove a microlocal inclusion relation for the generalized pullback (by a c-bounded generalized map) of Colombeau functions. The proof of this result relies on a stationary phase theorem for generalized phase functions, which is given in the Appendix. Furthermore we study an example (due to Hurd and Sattinger), where the pullback function stems from the generalized characteristic flow of a partial differential equation.      

Microlocal smoothing effect for the Schrödinger evolution equation in a Gevrey class

We discuss the microlocal Gevrey smoothing effect for the Schrödinger equation with variable coefficients via the propagation property of the wave front set of homogenous type. We apply the microlocal exponential estimates in a Gevrey case to prove our result.