Low Energy Effective Theory for Axion Strings

TL;DR

This paper examines the low energy effective theory of global cosmic strings, highlighting the limitations of traditional models and emphasizing the importance of including Goldstone excitations for realistic scenarios.

Contribution

It clarifies the applicability of Nambu-Gotto and Kalb-Ramond actions to cosmic strings and identifies the need for additional degrees of freedom in dynamic, realistic settings.

Findings

Formal equivalence for infinitely long strings

Limitations of collective coordinates in realistic cases

Necessity of low momentum Goldstone excitations

Abstract

We consider aspects of the low energy description of global cosmic strings. In the non-relativistic limit, we study the extent to which these are described by the combination of the Nambu-Gotto and Kalb-Ramond actions. While in a formal sense this is the case for infiniately long strings, for more realistic situations, the collective coordinates of the system do not provide a complete description for more than brief intervals; as time evolves it becomes necessary to include low momentum goldstone excitations as well.