Snowmass2021 Cosmic Frontier White Paper: Enabling Flagship Dark Energy Experiments to Reach their Full Potential

Understand

A new generation of powerful dark energy experiments will open new vistas for cosmology in the next decade.

• However, these projects cannot reach their utmost potential without data from other telescopes.
• This white paper focuses in particular on the compelling benefits of ground-based spectroscopic and photometric observations to complement the Vera C.
• Rubin Observatory, as well as smaller programs in aid of a DESI-2 experiment and CMB-S4.