Non-Relativistic Strings in Expanding Spacetime

TL;DR

This paper develops a non-relativistic string action in expanding spacetime, analyzes its dynamics, and models network properties, revealing unique scaling behaviors and potential relevance in physics contexts.

Contribution

It introduces a novel non-relativistic string action in FLRW backgrounds and explores the dynamics and network properties, including scaling and energy density effects.

Findings

Non-relativistic string networks exhibit scaling behavior.

Reduced string velocities lead to an equation of state without damping.

Enhanced energy densities are observed in non-relativistic string networks.

Abstract

We obtain a non-relativistic diffeomorphism invariant string action as a special limit of the Nambu-Goto action in an FLRW background. We use this action to study non-relativistic string dynamics in an expanding universe and construct an analytic model describing the macroscopic properties of non-relativistic string networks. The non-relativistic constraint equations allow arbitrarily small string velocities and thus a `frustrated' equation of state for non-interacting strings can be obtained without the need of a velocity damping mechanism. Assuming that colliding string segments reconnect by exchange of partners, non-relativistic string networks exhibit scaling behaviour, but with enhanced energy densities due to the reduced average string velocity. Non-relativistic string networks can be relevant in several contexts in condensed matter physics and cosmology.