From quantum gravity to gravitational waves through cosmic strings

TL;DR

This paper explores the connection between particle physics models that produce cosmic strings and quantum gravity, finding that simple models are incompatible with asymptotic safety, which aligns with recent gravitational wave data disfavoring cosmic strings.

Contribution

It investigates whether cosmic string-generating particle physics models can be embedded into an asymptotically safe quantum gravity framework, revealing significant constraints.

Findings

Simple models are incompatible with asymptotic safety.

Constraints on extended models are identified.

Recent gravitational wave data disfavors cosmic strings.

Abstract

New physics beyond the Standard Model can give rise to stochastic gravitational-wave backgrounds, for example through cosmic strings. In this way, gravitational-wave searches with pulsar-timing arrays as well as existing and future laser interferometers may provide information on particle physics beyond the Standard Model. Here, we take one additional step and link particle physics beyond the Standard Model to quantum gravity. We investigate whether particle physics models that may give rise to cosmic strings can be embedded into an asymptotically safe theory of quantum gravity and matter. We focus on models where cosmic strings arise from U(1)-symmetry-breaking in an extended Yukawa-Abelian-Higgs sector that may be part of a dark sector. We find a negative answer for the simplest model that can give rise to cosmic strings and also find constraints on an extended model. We tentatively conclude that cosmic strings are difficult to accommodate in asymptotically safe models. This fits well with the latest 15-year dataset and search for new physics from the NANOGrav collaboration, which disfavors a stable-cosmic-string interpretation. In that sense, the recent data provide an indirect, albeit at present rather tentative, hint about the quantum theory of gravity.