Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Gravitational Wave Experiments and Early Universe Cosmology

Michele Maggiore

TL;DR

This review comprehensively maps the landscape of gravitational-wave stochastic backgrounds, detailing how detectors respond to isotropic, stationary signals and how cross-correlation across a global detector network enhances sensitivity. It develops a coherent framework linking cosmological GW spectra to detector observables, and surveys theoretical sources—from inflationary relics to cosmic strings and phase transitions—while contrasting them with astrophysical backgrounds. The work highlights the nucleosynthesis and COBE bounds that constrain possible spectra, and outlines the practical paths—especially via advanced detectors and LISA—for probing early Universe physics through gravitational waves. Overall, it articulates the prospects and challenges of using GW backgrounds to access high-energy processes at times inaccessible by other means, emphasizing the crucial role of multi-detector correlations.

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.

Gravitational Wave Experiments and Early Universe Cosmology

TL;DR

This review comprehensively maps the landscape of gravitational-wave stochastic backgrounds, detailing how detectors respond to isotropic, stationary signals and how cross-correlation across a global detector network enhances sensitivity. It develops a coherent framework linking cosmological GW spectra to detector observables, and surveys theoretical sources—from inflationary relics to cosmic strings and phase transitions—while contrasting them with astrophysical backgrounds. The work highlights the nucleosynthesis and COBE bounds that constrain possible spectra, and outlines the practical paths—especially via advanced detectors and LISA—for probing early Universe physics through gravitational waves. Overall, it articulates the prospects and challenges of using GW backgrounds to access high-energy processes at times inaccessible by other means, emphasizing the crucial role of multi-detector correlations.

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.

Paper Structure

This paper contains 56 sections, 255 equations, 17 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Characterization of stochastic backgrounds of GWs
  3. The energy density $\Omega_{\rm gw} (f)$
  4. The spectral density $S_h(f)$ and the characteristic amplitudes $h_c(f)$
  5. The response of a single detector
  6. Detector tensor and detector pattern functions
  7. Interferometers
  8. Cylindrical bars
  9. Spherical detectors
  10. The strain sensitivity $\tilde{h}_f$
  11. Two-detectors correlation
  12. The overlap reduction functions $\gamma (f), \Gamma (f)$
  13. Optimal filtering
  14. The SNR for two-detectors correlations
  15. The characteristic noise $h_n(f)$ of correlated detectors
  16. ...and 41 more sections

Figures (17)

  • Figure 1: The planned LIGO sensitivity curve, in meters$/\sqrt{{\rm Hz}}$ (courtesy of the LIGO collaboration).
  • Figure 2: The planned VIRGO sensitivity curve (from ref. [16]).
  • Figure 3: The planned GEO sensitivity curve, without narrow-banding (courtesy of the GEO collaboration).
  • Figure 4: The planned GEO sensitivity curve, with narrow-banding at 600 Hz (courtesy of the GEO collaboration).
  • Figure 5: The planned advanced LIGO sensitivity curves, and the parameters relative to the various improvements, from ref. LSC (courtesy of the LIGO collaboration).
  • ...and 12 more figures