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arXiv · 2605.15347

The Tropical Moduli Space of Degree-3 Rational Maps

Tony Shaska·Mohammad-Reza Siadat
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Abstract

We construct and study the tropical moduli space \(\mathcal{M}_3^{\mathrm{trop}}\) of degree-$3$ tropical rational maps \(\mathbb{T}\PP^1 \to \mathbb{T}\PP^1\) up to post-composition. Using a combinatorial description in terms of slope sequences, we classify all such maps and show that there are exactly ten combinatorial types. This yields a polyhedral model of \(\mathcal{M}_3^{\mathrm{trop}}\) parametrized by gap lengths between break points. We determine the automorphism groups and obtain a stratification by explicit linear conditions. We also relate the construction to tropical Hurwitz theory and describe a natural compactification via degenerations of the parameters.

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Tony Shaska, Mohammad-Reza Siadat. 2026-05-14. The Tropical Moduli Space of Degree-3 Rational Maps. https://arxiv.org/abs/2605.15347

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