Semistable Reduction of Plane Quartics

The Stable Reduction Theorem guarantees that any smooth, projective, geometrically irreducible curve of genus $g \geq 2$ over a discretely valued field admits a unique stable model after a finite field extension.

Computing this model is a central problem in arithmetic geometry.

For non-hyperelliptic genus $3$ curves, which are canonically embedded as plane quartics, methods like admissible reduction become challenging in small residue characteristics.

This thesis establishes a precise connection between the abstractly defined stable model and computationally accessible GIT-stable plane models.

We prove that a GIT-stable plane model of a smooth plane quartic exists if and only if its stable reduction is non-hyperelliptic.

When this condition holds, we show that the stable model is the unique minimal semistable model that dominates the GIT-stable model.

The corresponding domination morphism is geometrically explicit: it contracts the $1$-tails of the stable reduction to cusps on the special fiber of the GIT-stable model and is an immersion elsewhere.

This result provides a geometric framework for computing the stable model by first finding a GIT-stable model and then resolving its cuspidal singularities.