On the boundary components of central streams in the two slopes case

Abstract

In 2004 Oort studied the foliation on the space of $p$-divisible groups. In his theory, special leaves called central streams play an important role. It is still meaningful to investigate central streams, for example, there remain a lot of unknown things on the boundaries of central streams. In this paper, we classify the boundary components of the central stream for a Newton polygon consisting of two segments, where one slope is less than $1/2$ and the other slope is greater than $1/2$. Moreover we determine the generic Newton polygon of each boundary component using this classification.