Automorphism Groups on Tropical Curves: Some Cohomology Calculations

Let $X$ be an abstract tropical curve and let $G$ be a finite subgroup of the automorphism group of $X$. Let $D$ be a divisor on $X$ whose equivalence class is $G$-invariant. We address the following question: is there always a divisor $D^{\mathrm{\prime }}$ in the equivalence class of $D$ which is $G$-invariant? Our main result is that the answer is “yes” for all abstract tropical curves. A key step in our proof is a tropical analogue of Hilbert’s Theorem 90.