LIGO Document P1300154-v25
- Gravitational-wave sources are predicted to superpose to create a stochastic background. This background is expected to contain unique information from throughout the history of the universe that is unavailable through standard astrophysical observations, making its study of fundamental importance to understanding the evolution of the universe. The latest data from LIGO and Virgo display no evidence of a stochastic gravitational-wave signal so we place direct 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5-1726 Hz. In the frequency band of 41.5-169.25 Hz, we constrain the energy density of the stochastic background, Omega_GW(f), to be less than 5.6x10^-6. For the 600-1000 Hz band, Omega_GW(f) is less than 0.14(f/900 Hz)^3, a factor of 2.5 lower than the best previously reported upper limits. Moreover, we found Omega_GW(f) to be less than 1.8x10^-4 for 170-600 Hz and less than 1.0(f/1300 Hz)^-3 for 1000-1726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the possible detection of inflationary gravitational waves.
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