Asymptotic Behavior of the Zhang--Kawazumi's phi-invariant

Abstract

The phi-invariant was introduced by Shou-Wu Zhang and Nariya Kawazumi. We study the continuity property of the phi-invariants for degenerating graphs, and show that this continuity property induces an adelic divisor on the moduli space of Riemann surfaces, and then give an asymptotic expression of the Zhang--Kawazumi's invariants for Riemann surfaces near the boundary of the moduli space. We mainly use Yuan--Zhang's adelic divisors, and follow Yuan's idea of globalization of phi-invariants.