Flows Without Pressure, Geometry and Turbulence
We start with the Cauchy problem for the multidimensional Burgers type equation with periodic boundary conditions. We introduce the notion of degeneracy for vector fields. Vector field $u$ is degenerate iff one of the following equivalent conditions holds: (*) the Jacoby matrix of $u$ is everywhere nilpotent (*) the pressureless Euler equation with the initial state $u$ is globally solvable in the class of $C1$-continuous functions. Non-degenerate initial states develops large spatial derivatives (turbulence). In 2D there is a nice geometric criterion for degeneracy due to Pogorelov cylinder theorem.