# Transplanckian Censorship and Global Cosmic Strings

## TL;DR

This paper explores the theoretical properties of supercritical cosmic strings in axion models, demonstrating their potential for topological inflation, nonsingular spacetimes, and implications for transplanckian censorship in the context of quantum gravity.

## Contribution

It connects effective field theory models of axion monodromy with classical spacetime analysis around supercritical cosmic strings, revealing conditions for topological inflation and censorship.

## Key findings

- Supercritical cosmic strings undergo topological inflation.
- Exterior spacetime is a nonsingular decompactifying cigar geometry.
- Signals can circumnavigate strings in exponentially long time.

## Abstract

Large field excursions are required in a number of axion models of inflation. These models also possess global cosmic strings, around which the axion follows a path mirroring the inflationary trajectory. Cosmic strings are thus an interesting theoretical laboratory for the study of transplanckian field excursions. We describe connections between various effective field theory models of axion monodromy and study the classical spacetimes around their supercritical cosmic strings. For small decay constants $f<M_p$ and large winding numbers $n>M_p/f$, the EFT is under control and the string cores undergo topological inflation, which may be either of exponential or power-law type. We show that the exterior spacetime is nonsingular and equivalent to a decompactifying cigar geometry, with the radion rolling in a potential generated by axion flux. Signals are able to circumnavigate infinite straight strings in finite but exponentially long time, $t\sim e^{\Delta a/M_p}$. For finite loops of supercritical string in asymptotically flat space, we argue that if topological inflation occurs, then topological censorship implies transplanckian censorship, or that external observers are forbidden from threading the loop and observing the full excursion of the axion.