**Authors**: Lam Hui, Sean T. McWilliams, I-Sheng Yang

**Date**: 11 Dec 2012

**Abstract**: Gravitational waves at suitable frequencies can resonantly interact with a binary system, inducing changes to its orbit. A stochastic gravitational-wave background causes the orbital elements of the binary to execute a classic random walk -- with the variance of orbital elements growing with time. The lack of such a random walk in binaries that have been monitored with high precision over long time-scales can thus be used to place an upper bound on the gravitational-wave background. Using periastron time data from the Hulse-Taylor binary pulsar spanning ~30 years, we obtain a bound of h_c < 7.9 x 10ˆ-14 at ~10ˆ-4 Hz, where h_c is the strain amplitude per logarithmic frequency interval. Our constraint complements those from pulsar timing arrays, which probe much lower frequencies, and ground-based gravitational-wave observations, which probe much higher frequencies. Interesting sources in our frequency band, which overlaps the lower sensitive frequencies of proposed space-based observatories, include white-dwarf/supermassive black-hole binaries in the early/late stages of inspiral, and TeV scale preheating or phase transitions. The bound improves as (time span)ˆ-2 and (sampling rate)ˆ-½. The Hulse-Taylor constraint can be improved to ~3.8 x 10ˆ-15 with a suitable observational campaign over the next decade. Our approach can also be applied to other binaries, including (with suitable care) the Earth-Moon system, to obtain constraints at different frequencies. The observation of additional binary pulsars with the SKA could reach a sensitivity of h_c ~ 3 x 10ˆ-17.

1212.2623
(/preprints)

2012-12-13, 08:45
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© M. Vallisneri 2012 — last modified on 2010/01/29

*Tantum in modicis, quantum in maximis*