The convergence Newton polygon of a $p$-adic differential equation IV : controlling graphs

Abstract

In our previous works we proved a finiteness property of the radii of convergence functions associated with a vector bundle with connection on $p$-adic analytic curves. We showed that the radii are locally constant functions outside a locally finite graph in the curve, called controlling graph. In this paper we refine that finiteness results by giving a bound on the size of the controlling graph in terms of the geometry of the curve and the rank of the module. This is based on super-harmonicity properties of radii of convergence and partial heights of the Newton polygon. Under suitable assumptions, we relate the size of the controlling graph associated with the total height of the convergence Newton polygon to the Euler characteristic in the sense of de Rham cohomology.