Gravitational Wave Experiments and Early Universe Cosmology

TL;DR

This paper reviews the experimental efforts and theoretical models for detecting stochastic gravitational wave backgrounds from the early universe, discussing sensitivities, limits, and cosmological sources.

Contribution

It provides a comprehensive overview of gravitational wave detection methods, sensitivities, and theoretical predictions from various early universe models, integrating experimental and theoretical perspectives.

Findings

Current detectors set upper limits on gravitational wave energy density.

Inflation and cosmic strings are significant sources of stochastic backgrounds.

Detection sensitivities vary across different experiments and correlation methods.

Abstract

Gravitational-wave experiments with interferometers and with resonant masses can search for stochastic backgrounds of gravitational waves of cosmological origin. We review both experimental and theoretical aspects of the search for these backgrounds. We give a pedagogical derivation of the various relations that characterize the response of a detector to a stochastic background. We discuss the sensitivities of the large interferometers under constructions (LIGO, VIRGO, GEO600, TAMA300, AIGO) or planned (Avdanced LIGO, LISA) and of the presently operating resonant bars, and we give the sensitivities for various two-detectors correlations. We examine the existing limits on the energy density in gravitational waves from nucleosynthesis, COBE and pulsars, and their effects on theoretical predictions. We discuss general theoretical principles for order-of-magnitude estimates of cosmological production mechanisms, and then we turn to specific theoretical predictions from inflation, string cosmology, phase transitions, cosmic strings and other mechanisms. We finally compare with the stochastic backgrounds of astrophysical origin.