Seminar talk, 29 March 2017
Speaker: Joseph Krasil'shchik
Title: Nonlocal symmetries of Lax integrable equations: a comparative study
We consider four three-dimensional equations: (1) the rdDym equation , (2) the 3D Pavlov equation ; (3) the universal hierarchy equation , and (4) the modified Veronese web equation . For each equation, using the know Lax pairs and expanding the latter in formal series in spectral parameter, we construct two infinite-dimensional differential coverings and give a full description of nonlocal symmetry algebras associated to these coverings. For all the four pairs of coverings, the obtained Lie algebras of symmetries manifest similar (but not the same) structures: the are (semi) direct sums of the Witt algebra, the algebra of vector fields on the line, and loop algebras; all of them contain a component of finite grading. We also discuss actions of recursion operators on shadows of nonlocal symmetries.