Parametric Resonances in Axionic Cosmic Strings

TL;DR

This paper discovers a new parametric resonance phenomenon in axionic cosmic strings, where internal mode excitations amplify transverse displacements, with implications for cosmic string network simulations.

Contribution

It introduces the first detailed analysis of parametric resonances in axionic cosmic strings through numerical simulations and analytical modeling.

Findings

Resonance amplifies string displacements significantly.

Massless and massive radiation are produced by excited strings.

Results align with effective Lagrangian predictions.

Abstract

In this letter we uncover a new parametric resonance of axionic cosmic strings. This process is triggered by the presence on the string of internal mode excitations that resonantly amplify the amplitude of transverse displacements of the string. We study this process by running numerical simulations that demonstrate the existence of this phenomenon in a $(3+1)$ dimensional lattice field theory and compare the results with the analytic expectations for the effective Lagrangian of the amplitude of these modes and their interactions. Finally, we also analyze the massless and massive radiation produced by these excited strings and comment on its relevance for the interpretation of the results of current numerical simulations of axionic cosmic string networks.