Cosmic archaeology with gravitational waves from cosmic strings

Yanou Cui,Marek Lewicki,James D Wells,David E Morrissey

doi:10.1103/physrevd.97.123505

Abstract

Cosmic strings are generic cosmological predictions of many extensions of the Standard Model of particle physics, such as a $U(1)^\prime$ symmetry breaking phase transition in the early universe or remnants of superstring theory. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the universe. We demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested. This work establishes a benchmark case that gravitational waves may provide an unprecedented, powerful tool for probing the evolutionary history of the very early universe.

Highlights

Gravitational waves (GW), vibrations of spacetime itself proposed by Einstein in 1916, were recently observed directly for the first time by the LIGO Collaboration [1]
If cosmic strings are realized in nature, they could provide a unique and powerful tool for probing the history of the early Universe
We have demonstrated that the frequency spectrum of GWs emitted by a cosmic string network depends dramatically on the energy content of the Universe when they are produced

Summary

INTRODUCTION

Gravitational waves (GW), vibrations of spacetime itself proposed by Einstein in 1916, were recently observed directly for the first time by the LIGO Collaboration [1]. The standard thermal picture for the evolution of the cosmos is primordial inflation followed by reheating to a high temperature, and a subsequent long period in which the expansion of the Universe is driven by a dominant energy density of radiation until the more recent transitions to matter and dark energy domination. Evidence for this “standard cosmology” comes primarily from observations of the CMB [34] and the successful predictions of big bang nucleosynthesis (BBN), corresponding to cosmic temperatures up to T ≃ 5 MeV [35]. We show that a combination of current and planned GW detectors with different frequency sensitivities may enable us to reconstruct a timeline of cosmic history well beyond the BBN epoch

GW FROM COSMIC STRINGS

TESTS OF THE STANDARD COSMOLOGY

Findings

DISCUSSION