Explicit formula for the solution of the Szegö equation on the real line and applications

Oana Pocovnicu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)


We consider the cubic Szego equation

i partial derivative(t)u = Pi (vertical bar u vertical bar(2)u)

in the Hardy space L(+)(2) ( R) on the upper half-plane, where Pi is the Szego projector. It is a model for totally non-dispersive evolution equations and is completely integrable in the sense that it admits a Lax pair. We find an explicit formula for solutions of the Szego equation. As an application, we prove soliton resolution in H(s) for all s >= 0, for generic rational function data. As for nongeneric data, we construct an example for which soliton resolution holds only in H(s), 0 +/-infinity parallel to u(t)parallel to H(s) = infinity ; s > 1/2 : As a second application, we construct explicit generalized action-angle coordinates by solving the inverse problem for the Hankel operator H(u) appearing in the Lax pair. In particular, we show that the trajectories of the Szego equation with generic rational function data are spirals around Lagrangian toroidal cylinders T(N) x R(N).

Original languageEnglish
Pages (from-to)607-649
Number of pages43
JournalDiscrete and Continuous Dynamical Systems-Series A
Issue number3
Publication statusPublished - Nov 2011


  • Szego equation
  • integrable systems
  • Lax pair
  • Hankel operators
  • soliton resolution
  • action-angle coordinates


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