Constraining the gravitational-wave energy density of the Universe in the range 0.1 Hz to 1 Hz using the Apollo Seismic Array

In this paper, we describe an analysis of Apollo-era lunar seismic data that places an upper limit on an isotropic stochastic gravitational-wave background integrated over a year in the frequency range 0.1-1 Hz. We find that because the Moon's ambient noise background is much quieter than that of the Earth, significant improvements over an Earth-based analysis were made. We find an upper limit of ΩGW<1.2×105, which is 3 orders of magnitude smaller than a similar analysis of a global network of broadband seismometers on Earth and the best limits in this band to date. We also discuss the benefits of a potential Earth-Moon correlation search and compute the time-dependent overlap reduction function required for such an analysis. For this search, we find an upper limit an order of magnitude larger than the Moon-Moon search.