Understanding ramification of branched {$\mathbb{Z}_p$}-covers

Abstract

We provide a combinatorial approach to counting the number of spanning trees at the $n$-th layer of a branched $\mathbb{Z}_p$-cover of a finite connected graph $\mathsf{X}$. Our method achieves in explaining how the position of the ramified vertices affects the count and hence the Iwasawa invariants. We do so by introducing the notion of segments, segmental decomposition of a graph, and number of segmental $t$-tree spanning forests.