Constraints on cosmic strings using data from the first Advanced LIGO observing run

TL;DR

This paper searches for gravitational waves from cosmic string loops in LIGO data, sets upper limits on string parameters, and combines multiple astrophysical data sets to constrain cosmic string models.

Contribution

It provides the first constraints on cosmic string parameters using Advanced LIGO O1 data and combines multiple observational methods for comprehensive limits.

Findings

No gravitational wave signals detected from cosmic strings in LIGO data.

Upper limits placed on cosmic string tension and intercommutation probability.

Large parts of the parameter space for cosmic string models are excluded.

Abstract

Cosmic strings are topological defects which can be formed in GUT-scale phase transitions in the early universe. They are also predicted to form in the context of string theory. The main mechanism for a network of Nambu-Goto cosmic strings to lose energy is through the production of loops and the subsequent emission of gravitational waves, thus offering an experimental signature for the existence of cosmic strings. Here we report on the analysis conducted to specifically search for gravitational-wave bursts from cosmic string loops in the data of Advanced LIGO 2015-2016 observing run (O1). No evidence of such signals was found in the data, and as a result we set upper limits on the cosmic string parameters for three recent loop distribution models. In this paper, we initially derive constraints on the string tension $G\mu$ and the intercommutation probability, using not only the burst analysis performed on the O1 data set, but also results from the previously published LIGO stochastic O1 analysis, pulsar timing arrays, cosmic microwave background and Big-Bang nucleosynthesis experiments. We show that these data sets are complementary in that they probe gravitational waves produced by cosmic string loops during very different epochs. Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider.