The gravitational wave landscape of cosmic string networks with varying tension

TL;DR

This paper classifies gravitational wave signals from cosmic string networks with varying tension, providing spectral index calculations, concrete string theory examples, and bounds from Swampland constraints.

Contribution

It offers a comprehensive classification of gravitational wave phenomenology from variable-tension cosmic strings, including concrete string theory models and theoretical bounds.

Findings

Spectral indices of stochastic gravitational wave backgrounds derived.

Concrete examples from type IIB string theory with dynamical branes.

Swampland constraints impose bounds on tension variation and spectral features.

Abstract

We fully classify the phenomenology of gravitational wave emission from scaling cosmic string networks with varying tension and compute the spectral indices of the resulting stochastic backgrounds. In string compactifications, periods of varying tension occur when moduli acquire a time-dependence. We present concrete examples in type IIB string theory as D3- and NS5- branes wrapping internal cycles, which become dynamical due to the effect of moduli potentials. Moreover, we use Swampland constraints to derive general bounds on the allowed time-variation of the effective string tension in FLRW backgrounds and on the resulting spectral indices.