On the gravitational, dilatonic and axionic radiative damping of cosmic strings

TL;DR

This paper investigates the radiation damping effects on cosmic strings caused by dilatonic, gravitational, and axionic waves, revealing that local approximations can lead to antidamping or zero damping, with implications for string network simulations.

Contribution

It demonstrates that a local back reaction approximation yields antidamping for axionic fields and zero damping for gravitational fields, proposing a modified approach for better simulation accuracy.

Findings

Dilatonic damping is positive and significant.

Axionic fields exhibit antidamping with the local approximation.

Gravitational damping is effectively zero in the proposed model.

Abstract

We study the radiation reaction on cosmic strings due to the emission of dilatonic, gravitational and axionic waves. After verifying the (on average) conservative nature of the time-symmetric self-interactions, we concentrate on the finite radiation damping force associated with the half-retarded minus half-advanced ``reactive'' fields. We revisit a recent proposal of using a ``local back reaction approximation'' for the reactive fields. Using dimensional continuation as convenient technical tool, we find, contrary to previous claims, that this proposal leads to antidamping in the case of the axionic field, and to zero (integrated) damping in the case of the gravitational field. One gets normal positive damping only in the case of the dilatonic field. We propose to use a suitably modified version of the local dilatonic radiation reaction as a substitute for the exact (non-local) gravitational radiation reaction. The incorporation of such a local approximation to gravitational radiation reaction should allow one to complete, in a computationally non-intensive way, string network simulations and to give better estimates of the amount and spectrum of gravitational radiation emitted by a cosmologically evolving network of massive strings.