Curvature diffusion of planar curves with generalised Neumann boundary conditions inside cones

Abstract

We study families of smooth immersed regular planar curves $ \alpha : \left [-1,1 \right ]\times \left [0,T \right )\to \mathbb{R}^{2}$ satisfying the fourth order nonlinear curve diffusion flow with generalised Neumann boundary conditions inside cones. We show that if the initial curve has sufficiently small oscillation of curvature then this remains so under the flow. Such families of evolving curves either exist for a finite time, when an end of the curve has reached the tip of the cone or the curvature has become unbounded in $L^2$, or they exist for all time and converge exponentially in the $C^{\infty}$- topology to a circular arc that, together with the cone boundary encloses the same area as that of the initial curve and cone boundary. The same kind of result is possible for the higher order polyharmonic curve diffusion flows with appropriate boundary conditions; in particular in the sixth order case the smallness condition on the oscillation of curvature is exactly the same as for curve diffusion.