9 research outputs found
Functional model for extensions of symmetric operators and applications to scattering theory
On the basis of the explicit formulae for the action of the unitary group of exponentials corresponding to almost solvable extensions of a given closed symmetric operator with equal deficiency indices, we derive a new representation for the scattering matrix for pairs of such extensions. We use this representation to explicitly recover the coupling constants in the inverse scattering problem for a finite non-compact quantum graph with δ-type vertex conditions.</p
Functional model for extensions of symmetric operators and applications to scattering theory
On the basis of the explicit formulae for the action of the unitary group of
exponentials corresponding to almost solvable extensions of a given closed
symmetric operator with equal deficiency indices, we derive a new
representation for the scattering matrix for pairs of such extensions. We use
this representation to explicitly recover the coupling constants in the inverse
scattering problem for a finite non-compact quantum graph with -type
vertex conditions.Comment: 28 page
Operator-norm resolvent asymptotic analysis of continuous media with high-contrast inclusions
Using a generalisation of the classical notion of Dirichlet-to-Neumann map
and the related formulae for the resolvents of boundary-value problems, we
analyse the asymptotic behaviour of solutions to a "transmission problem" for a
high-contrast inclusion in a continuous medium, for which we prove the
operator-norm resolvent convergence to a limit problem of "electrostatic" type
for functions that are constant on the inclusion. In particular, our results
imply the convergence of the spectra of high-contrast problems to the spectrum
of the limit operator, with order-sharp convergence estimates.Comment: 15 pages, 1 figure. Continuation of: arXiv:1907.08144. As accepted
by: Math. Note
Scattering theory for a class of non-selfadjoint extensions of symmetric operators
This work deals with the functional model for a class of extensions of
symmetric operators and its applications to the theory of wave scattering. In
terms of Boris Pavlov's spectral form of this model, we find explicit formulae
for the action of the unitary group of exponentials corresponding to almost
solvable extensions of a given closed symmetric operator with equal deficiency
indices. On the basis of these formulae, we are able to construct wave
operators and derive a new representation for the scattering matrix for pairs
of such extensions in both self-adjoint and non-self-adjoint situations.Comment: 32 pages; This is the continuation of arXiv:1703.06220 (and formerly
contained in v1); this version is as accepted by the journal (Operator
Theory: Advances and Applications
Functional model for boundary-value problems and its application to the spectral analysis of transmission problems
We develop a functional model for operators arising in the study of
boundary-value problems of materials science and mathematical physics. We
provide explicit formulae for the resolvents of the associated extensions of
symmetric operators in terms of the associated generalised Dirichlet-to-Neumann
maps, which can be utilised in the analysis of the properties of
parameter-dependent problems as well as in the study of their spectra.Comment: 30 pages, 1 figur
Spectral enclosures for non-self-adjoint extensions of symmetric operators
The spectral properties of non-self-adjoint extensions A[B] of a symmetric operator in a Hilbert space are studied with the help of ordinary and quasi boundary triples and the corresponding Weyl functions. These extensions are given in terms of abstract boundary conditions involving an (in general non-symmetric) boundary operator B. In the abstract part of this paper, sufficient conditions for sectoriality and m-sectoriality as well as sufficient conditions for A[B] to have a non-empty resolvent set are provided in terms of the parameter B and the Weyl function. Special attention is paid to Weyl functions that decay along the negative real line or inside some sector in the complex plane, and spectral enclosures for A[B] are proved in this situation. The abstract results are applied to elliptic differential operators with local and non-local Robin boundary conditions on unbounded domains, to Schrödinger operators with δ-potentials of complex strengths supported on unbounded hypersurfaces or infinitely many points on the real line, and to quantum graphs with non-self-adjoint vertex couplings