# Effective bilipschitz bounds on drilling and filling

## TL;DR

This paper establishes explicit bilipschitz bounds on how the metric of a hyperbolic 3-manifold changes under long Dehn fillings, with applications to Margulis numbers, systoles, and cosmetic surgery conjecture.

## Contribution

It provides quantitative bounds on metric changes during Dehn fillings, extending previous qualitative results, and applies these bounds to problems in 3-manifold topology.

## Key findings

- Bounds relate Margulis numbers of N and its fillings
- Lower bound on systole for manifolds with small Margulis number
- Explicit upper bounds on slopes for cosmetic surgeries

## Abstract

This paper proves explicit bilipschitz bounds on the change in metric between the thick part of a cusped hyperbolic 3-manifold N and the thick part of any of its long Dehn fillings. Given a bilipschitz constant J > 1 and a thickness constant epsilon > 0, we quantify how long a Dehn filling suffices to guarantee a J-bilipschitz map on epsilon-thick parts. A similar theorem without quantitative control was previously proved by Brock and Bromberg, applying Hodgson and Kerckhoff's theory of cone deformations. We achieve quantitative control by bounding the analytic quantities that control the infinitesimal change in metric during the cone deformation. Our quantitative results have two immediate applications. First, we relate the Margulis number of N to the Margulis numbers of its Dehn fillings. In particular, we give a lower bound on the systole of any closed 3-manifold M whose Margulis number is less than 0.29. Combined with Shalen's upper bound on the volume of such a manifold, this gives a procedure to compute the finite list of 3-manifolds whose Margulis numbers are below 0.29. Our second application is to the cosmetic surgery conjecture. Given the systole of a one-cusped hyperbolic manifold N, we produce an explicit upper bound on the length of a slope involved in a cosmetic surgery on N. This reduces the cosmetic surgery conjecture on N to an explicit finite search.