Multiple singular values of Hankel operators

Patrick Gerard (1) , Sandrine Grellier (2)

1 LM-Orsay - Laboratoire de Mathématiques d'Orsay
2 MAPMO - Mathématiques - Analyse, Probabilités, Modélisation - Orléans

The goal of this paper is to construct a nonlinear Fourier transformation on the space of symbols of compact Hankel operators on the circle. This transformation allows to solve a general inverse spectral problem involving singular values of a compact Hankel operator, with arbitrary multiplicities. The formulation of this result requires the introduction of the pair made with a Hankel operator and its shifted Hankel operator. As an application, we prove that the space of symbols of compact Hankel operators on the circle admits a singular foliation made of tori of finite or infinite dimensions, on which the flow of the cubic Szegö equation acts. In particular, we infer that arbitrary solutions of the cubic Szegö equation on the circle with finite momentum are almost periodic with values in H^{1/2}(S ^1).

Mots clés: Hankel operators; inverse spectral problems; inverse spectral transform; cubic Szegö equation

Domaines: Equations aux dérivées partielles [math.AP]; Théorie spectrale [math.SP]

Patrick Gerard, Sandrine Grellier. Multiple singular values of Hankel operators. 2014. ⟨hal-00943396⟩