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Searching for a Stochastic Background of Gravitational Waves with LIGO

LIGO Scientific Collaboration

TL;DR

This paper reports a Bayesian 90% upper limit on the stochastic gravitational-wave background using LIGO S4 data, achieving $Ω_0 < 6.5 \times 10^{-5}$ in the 51–150 Hz band and a combined estimate of $Ω_0 = (-0.8 \pm 4.3) \times 10^{-5}$ when instrumental correlations are carefully controlled. The analysis employs a cross-correlation framework with an optimal filter, interval-based PSD estimation, and data-quality cuts, validated by hardware and software injections. The work places the result in the context of complementary bounds from CMB, pulsar timing, Cassini Doppler tracking, and BBN, and demonstrates sensitivity to models of cosmic strings and pre-big-bang cosmologies while outlining prospects for S5 and Advanced LIGO to surpass indirect bounds. Overall, the study advances direct high-frequency constraints on the stochastic GW background and informs future efforts to probe fundamental cosmological processes through gravitational waves.

Abstract

The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new limit is $Ω_{\rm GW} < 6.5 \times 10^{-5}$. This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.

Searching for a Stochastic Background of Gravitational Waves with LIGO

TL;DR

This paper reports a Bayesian 90% upper limit on the stochastic gravitational-wave background using LIGO S4 data, achieving in the 51–150 Hz band and a combined estimate of when instrumental correlations are carefully controlled. The analysis employs a cross-correlation framework with an optimal filter, interval-based PSD estimation, and data-quality cuts, validated by hardware and software injections. The work places the result in the context of complementary bounds from CMB, pulsar timing, Cassini Doppler tracking, and BBN, and demonstrates sensitivity to models of cosmic strings and pre-big-bang cosmologies while outlining prospects for S5 and Advanced LIGO to surpass indirect bounds. Overall, the study advances direct high-frequency constraints on the stochastic GW background and informs future efforts to probe fundamental cosmological processes through gravitational waves.

Abstract

The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new limit is . This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.

Paper Structure

This paper contains 13 sections, 9 equations, 16 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Analysis
  3. Cross-Correlation Method
  4. Identification of Correlated Instrumental Lines
  5. Data Quality Cuts
  6. Results
  7. New Upper Limit
  8. Signal Injections
  9. Implications
  10. Complementarity with Other Measurements and Observations
  11. Implications for Cosmic Strings Models
  12. Implications for Pre-Big-Bang Models
  13. Conclusions

Figures (16)

  • Figure 2: Typical strain amplitude spectra of LIGO interferometers during the science run S4 (solid curves top-to-bottom at 70 Hz: H2, L1, H1). The black dashed curve is the LIGO sensitivity goal. The gray dashed curve is the strain amplitude spectrum corresponding to the limit presented in this paper for the frequency-independent GW spectrum $\Omega_0 < 6.5 \times 10^{-5}$.
  • Figure 3: Overlap reduction function for the Hanford-Hanford pair (black solid) and for the Hanford-Livingston pair (gray dashed).
  • Figure 4: Coherence calculated for the H1L1 pair (top) and for the H2L1 pair (bottom) over all of S4 data for 1 mHz resolution and 100 mHz resolution. The horizontal dashed lines indicate $1/N_{avg}$ - the expected level of coherence after averaging over $N_{avg}$ time-periods with uncorrelated spectra. The line at 376 Hz is one of the simulated pulsar lines.
  • Figure 5: Histogram of the coherence for H1L1 (top) and H2L1 (bottom) at 1 mHz resolution follows the expected exponential distribution, with exponent coefficient $N_{avg}$ (the number of time-periods over which the average is made).
  • Figure 6: Trend of $\sigma_{Y_I}$ over the whole S4 run for the 192-sec intervals of H1L1 pair. The dashed line denotes the large $\sigma$ cut: segments lying above this line are removed from analysis. Note the daily variation in the sensitivity of this pair.
  • ...and 11 more figures