Detecting the Cosmic Gravitational Wave Background with the Big Bang Observer

TL;DR

This paper analyzes how a proposed space-based interferometer, the Big Bang Observer, can detect the Cosmic Gravitational Background by optimizing the signal-to-noise ratio using multiple interferometry variables.

Contribution

It extends previous cross-correlation studies by calculating the optimal SNR for a six-link triangular interferometer, showing detector orientation independence.

Findings

BBO could detect a gravitational wave background with a_{gw} > 2.2 imes 10^{-17}

Optimal combination of interferometry variables enhances detection sensitivity

Detector orientation does not affect SNR in the full variable set.

Abstract

The detection of the Cosmic Microwave Background Radiation (CMB) was one of the most important cosmological discoveries of the last century. With the development of interferometric gravitational wave detectors, we may be in a position to detect the gravitational equivalent of the CMB in this century. The Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic, making it difficult to distinguish from instrument noise. The contribution from the CGB can be isolated by cross-correlating the signals from two or more independent detectors. Here we extend previous studies that considered the cross-correlation of two Michelson channels by calculating the optimal signal to noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer. In contrast to the two channel case, we find that the relative orientation of a pair of coplanar detectors does not affect the signal to noise ratio. We apply our results to the detector design described in the Big Bang Observer (BBO) mission concept study and find that BBO could detect a background with $\Omega_{gw} > 2.2 \times 10^{-17}$.