Snowmass2021-Letter of Interest A deci-Hz Gravitational-Wave Lunar Observatory for Cosmology

We are proposing Gravitational-wave Lunar Observatory for Cosmology (GLOC) [1] – a first of its kind fundamental physics experiment on the surface of the Moon. The experiment would access gravitational-waves (GWs) in the frequency range of deci-Hz to 5 Hz, a challenging regime for all Earthbased detectors and space missions. We find that such a lunar-based experiment can survey & 70% of the observable volume of our universe without significant background contamination. This unprecedented sensitivity makes GLOC a powerful cosmic probe for Dark Energy, Dark Matter and physics beyond the Standard Model. In particular, it will independently trace the Hubble expansion rate up to redshift z ∼ 3, provide the strongest limits on the sub-solar Dark Matter candidates and test ΛCDM cosmology up to z ∼ 100. Furthermore, it will have a unique access to GWs from Type Ia supernovae, thus aiding calibration of the standard candles.