Self-adjoint Pseudodifferential Operator Research Articles

Invariant subspaces of elliptic systems II: Spectral theory

Consider an elliptic self-adjoint pseudodifferential operator $A$ acting on $m$-columns of half-densities on a closed manifold $M$ M, whose principal symbol is assumed to have simple eigenvalues.We show that the spectrum of $A$ decomposes, up to an error with superpolynomial decay, into $m$ distinct series, each associated with one of the eigenvalues of the principal symbol of $A$. These spectral results are then applied to the study of propagation of singularities in hyperbolic systems. The key technical ingredient is the use of the carefully devised pseudodifferential projections introduced in the first part of this work, which decompose $L^2 (M)$ into almost-orthogonal almost-invariant subspaces under the action of both $A$ and the hyperbolic evolution.

Invariant subspaces of elliptic systems I: Pseudodifferential projections

Consider an elliptic self-adjoint pseudodifferential operator A acting on m-columns of half-densities on a closed manifold M, whose principal symbol is assumed to have simple eigenvalues. We show existence and uniqueness of m orthonormal pseudodifferential projections commuting with the operator A and provide an algorithm for the computation of their full symbols, as well as explicit closed formulae for their subprincipal symbols. Pseudodifferential projections yield a decomposition of L2(M) into invariant subspaces under the action of A modulo C∞(M). Furthermore, they allow us to decompose A into m distinct sign definite pseudodifferential operators. Finally, we represent the modulus and the Heaviside function of the operator A in terms of pseudodifferential projections and discuss physically meaningful examples.

Diagonalization of elliptic systems via pseudodifferential projections

Consider an elliptic self-adjoint pseudodifferential operator A acting on m-columns of half-densities on a closed manifold M, whose principal symbol is assumed to have simple eigenvalues. Relying on a basis of pseudodifferential projections commuting with A, we construct an almost-unitary pseudodifferential operator that diagonalizes A modulo an infinitely smoothing operator. We provide an invariant algorithm for the computation of its full symbol, as well as an explicit closed formula for its subprincipal symbol. Finally, we give a quantitative description of the relation between the spectrum of A and the spectrum of its approximate diagonalization, and discuss the implications at the level of spectral asymptotics.

Fundamental solutions and Hadamard states for a scalar field with arbitrary boundary conditions on an asymptotically AdS spacetimes

We consider the Klein-Gordon operator on an n-dimensional asymptotically anti-de Sitter spacetime (M,g) together with arbitrary boundary conditions encoded by a self-adjoint pseudodifferential operator on ∂M of order up to 2. Using techniques from b-calculus and a propagation of singularities theorem, we prove that there exist advanced and retarded fundamental solutions, characterizing in addition their structural and microlocal properties. We apply this result to the problem of constructing Hadamard two-point distributions. These are bi-distributions which are weak bi-solutions of the underlying equations of motion with a prescribed form of their wavefront set and whose anti-symmetric part is proportional to the difference between the advanced and the retarded fundamental solutions. In particular, under a suitable restriction of the class of admissible boundary conditions and setting to zero the mass, we prove their existence extending to the case under scrutiny a deformation argument which is typically used on globally hyperbolic spacetimes with empty boundary.

On the convergence of the means spectral expansions corresponding to the pseudo-differential operators for distributions from the Sobolev–Liouville classes

We study the convergence of means of spectral expansions corresponding to positive self-adjoint elliptic pseudo-differential operators for distributions from the Sobolev–Liouville class.

Asymptotics of Spectra of Compact Pseudodifferential Operators with Nonsmooth Symbols with Respect to Spatial Variables

We consider compact selfadjoint pseudodifferential operators with symbols that are not smooth with respect to x on a fixed set. We obtain conditions for the validity of the Weyl formula for the spectral asymptotics and apply the results to some class of pseudodifferential operators.

$Q$-prime curvature and scattering theory on strictly pseudoconvex domains

The $Q$-prime curvature is a local invariant of pseudo-Einstein contact forms on integrable strictly pseudoconvex CR manifolds. The transformation law of the $Q$-prime curvature under scaling is given in terms of a differential operator, called the $P$-prime operator, acting on the space of CR pluriharmonic functions. In this paper, we generalize these objects to the boundaries of asymptotically complex hyperbolic Einstein (ACHE) manifolds, which are partially integrable, strictly pseudoconvex CR manifolds, by using the scattering matrix for ACHE manifolds. In this setting, the $P$-prime operator is a self-adjoint pseudodifferential operator acting on smooth functions and the $Q$-prime curvature is globally determined by the ACHE manifold and the choice of a contact form on the boundary. We prove that the integral of the $Q$-prime curvature is a conformal primitive of the $Q$-curvature; in particular, it defines an invariant of ACHE manifolds whose boundaries admit a contact form with zero $Q$-curvature. We also apply the generalized $Q$-prime curvature to compute the renormalized volume of strictly pseudoconvex domains whose boundaries may not admit pseudo-Einstein structure.

Universal Components of Random Nodal Sets

We give, as $L$ grows to infinity, an explicit lower bound of order $L^{n/m}$ for the expected Betti numbers of the vanishing locus of a random linear combination of eigenvectors of $P$ with eigenvalues below $L$. Here, $P$ denotes an elliptic self-adjoint pseudo-differential operator of order $m\textgreater{}0$, bounded from below and acting on the sections of a Riemannian line bundle over a smooth closed $n$-dimensional manifold $M$ equipped with some Lebesgue measure. In fact, for every closed hypersurface $\Sigma$ of $\mathbb R^n$, we prove that there exists a positive constant $p\_\Sigma$ depending only on $\Sigma$, such that for every large enough $L$ and every $x\in M$, a component diffeomorphic to $\Sigma$ appears with probability at least $p\_\Sigma$ in the vanishing locus of a random section and in the ball of radius $L^{-1/m}$ centered at $x$. These results apply in particular to Laplace-Beltrami and Dirichlet-to-Neumann operators.

Asymptotic Behavior of the Spectrum of Pseudodifferential Operators of Variable Order

We consider compact selfadjoint pseudodifferential operators under the assumption that the decay order of symbols with respect to ξ depends on a point x. We show that the asymptotic Weyl formula is valid for such operators. Bibliography: 12 titles.

The Splitting of the Domain of the Definition of the Elliptic Self-Adjoint Pseudodifferential Operator

In this work we researched domain splitting of self-adjoint elliptic pseudodifferential operator. In particular the Laplace -- Beltrami operator in the space of smooth differential $k$-forms defined on a smooth compact oriented Riemannian manifold without boundary be such operator. This result can be used in model with Sobolev type equations.

Betti numbers of random nodal sets of elliptic pseudo-differential operators

Given an elliptic self-adjoint pseudo-differential operator $P$ bounded from below, acting on the sections of a Riemannian line bundle over a smooth closed manifold $M$ equipped with some Lebesgue measure, we estimate from above, as $L$ grows to infinity, the Betti numbers of the vanishing locus of a random section taken in the direct sum of the eigenspaces of $P$ with eigenvalues below $L$. These upper estimates follow from some equidistribution of the critical points of the restriction of a fixed Morse function to this vanishing locus. We then consider the examples of the Laplace-Beltrami and the Dirichlet-to-Neumann operators associated to some Riemannian metric on $M$.

Complete Asymptotic Expansion of the Integrated Density of States of Multidimensional Almost-Periodic Pseudo-Differential Operators

We obtain a complete asymptotic expansion of the integrated density of states of operators of the form $${H = (-\Delta)^w+ B}$$ in $${\mathbb{R}^d}$$ . Here w > 0 and B belong to a wide class of almost-periodic self-adjoint pseudo-differential operators of order less than 2w. In particular, we obtain such an expansion for magnetic Schrödinger operators with either smooth periodic or generic almost-periodic coefficients.

Complete asymptotic expansion of the integrated density of states of multidimensional almost-periodic Schrödinger operators

We obtain a complete asymptotic expansion of the integrated density of states of operators of the form \({H = (-\Delta)^w+ B}\) in \({\mathbb{R}^d}\) . Here w > 0 and B belong to a wide class of almost-periodic self-adjoint pseudo-differential operators of order less than 2w. In particular, we obtain such an expansion for magnetic Schrodinger operators with either smooth periodic or generic almost-periodic coefficients.

Bethe-Sommerfeld conjecture for periodic operators with strong perturbations

We consider a periodic self-adjoint pseudo-differential operator $H=(-\Delta)^m+B$, $m>0$, in $\R^d$ which satisfies the following conditions: (i) the symbol of $B$ is smooth in $\bx$, and (ii) the perturbation $B$ has order less than $2m$. Under these assumptions, we prove that the spectrum of $H$ contains a half-line. This, in particular implies the Bethe-Sommerfeld Conjecture for the Schr\"odinger operator with a periodic magnetic potential in all dimensions.

On the Positive Parts of Second Order Symmetric Pseudodifferential Operators

Using microlocalization, the positive and the negative parts for a class of second order formally self-adjoint pseudodifferential operators are constructed.

An extension of the work of V. Guillemin on complex powers and zeta functions of elliptic pseudodifferential operators

The purpose of this note is to extend the methods and results of Guillemin on elliptic self-adjoint pseudodifferential operators of order one, from operators defined on smooth functions on a closed manifold to operators defined on smooth sections in a vector bundle. The case of bundles of Hilbert modules of finite type over a finite von Neumann algebra will also be treated.

Functions of Pseudo-Differential Operators of Non-positive Order

The aim of this paper is to define functions of several commuting and non-commuting self-adjoint pseudo-differential operators of non-positive order, by means of the H. Weyl formula[formula]Given 1<p<∞, the pseudo-differential operators under consideration belong to the Hörmander classLmρ, δ,m⩽−n(1−ρ|(1/p)−(1/2)|, 0<ρ⩽1, 0⩽δ<1,δ⩽ρand act on functions defined on the euclidean space Rn.

ESTIMATES OF THE SPECTRUM OF COMPACT PSEUDODIFFERENTIAL OPERATORS IN UNBOUNDED DOMAINS

We study the spectrum of compact selfadjoint pseudodifferential operators with matrix symbol in unbounded sets in Euclidean space. Two-sided bounds for the spectrum are obtained by the variational method. Additional regularity assumptions on the symbol lead to a formula for the spectral asymptotics with a remainder term estimate.

The spectrum of a one-dimensional pseudo-differential operator

AbstractWe describe the spectrum of a self-adjoint pseudo-differential operator on L2 (– ∞, ∞). We show that the essential spectrum coincides with the interval ([1, ∞) and give a lower bound for the lowest eigenvalue in (– ∞, 1). A sufficient condition for the existence of an eigenvalue in (– ∞, 1) is also given.

Spectral asymptotic behavior of elliptic systems

One investigates a first-order elliptic self-adjoint pseudodifferential operator A (x,D) acting in sections of a Hermitian vector bundle over a compactn-dimensional manifold x. It is assumed that the principal symbol A(x, ξ) of the operator is locally diagonalizable and that its eigenvaluesaj(x, ξ) have a variable multiplicity and that {ai,ak}≠0 wheneverai=ak. Under indicated conditions one constructs an expansion of the fundamental solution of the hyperbolic system\(i\frac{{\partial u}}{{\partial t}} = A(x,D)u\) and one investigates the asymptotic properties of the spectrum of the operator A (x,D). For the distribution functionN(λ) of the eigenvalues one establishes that . Under further assumptions on the properties of the bicharacteristic of the symbolsaj(x, ξ) one establishes a stronger estimate of Duistermaat-Guillemin type:N(λ)=Cλn+C′λn−i+0(γn−1)