Alexander Val. ANTONIOUK
Department of Nonlinear Analysis,
Institute of Mathematics of NAS of Ukraine,
Tereshchenkivs'ka Str. 3,
01601 Kyiv-4, UKRAINE

Nonlinear symmetries of variational calculus and regularity properties of differential flows on non-compact manifolds

    This talk is devoted to the discussion of symmetries that arise in the high order variational equations. Such symmetries lead to a new class of nonlinear estimates  on variations and permit the work in the case of essentially non-Lipschitz nonlinear differential equations, i.e. when the classical Cauchy-Liouville- Picard regularity scheme fails to work.
   These estimates are applied to the problem of C differentiability with respect to the initial data and parameters for the nonlinear differential flows on manifolds, that could also contain random terms. In particular, we demonstrate that the geometrically correct study of regularity problems for nonlinear flows on manifolds requires introduction of a new type variations with respect to the initial data. These variations are defined via a natural generalization of covariant Riemannian derivatives.
   We also find how the curvature manifests in the structure of the high order variational equations.