We present the Snowmass 2021 strategy to delve deep, search wide, and aim high for new discoveries at the Cosmic Frontier of particle physics. The Cosmic Frontier is the bedrock of High Energy Physics in the twenty-first century, providing evidence for Beyond the Standard Model physics that motivates much of the Snowmass 2021 program across all frontiers. The scientific scope of the Cosmic Frontier encompasses four of the five science drivers of the field: dark matter, dark energy and cosmic acceleration, neutrinos, and exploring the unknown in search of new particles, new fields, and new principles of Nature. Covering a time frame of 20 years, our plan features a portfolio of small, medium, and large projects which are ready to produce a continuous stream of groundbreaking science results within this decade along with pathfinders for the next generation of projects to come in the following decade. In this report, we articulate the fundamental questions to be addressed for each science driver and identify key measurements required to achieve well-defined scientific thresholds for discovery. We describe the ecosystem of experiments designed to obtain those measurements as well as the associated developments in theory and technology. We plan to delve deep in sensitivity and search wide across many orders of magnitude in mass to discover the particle nature of dark matter. Moreover, we aim high, through billions of light years of cosmic history, to discover the time-evolution of dark energy, make the first experimental observations of the physics of inflation, and search for new physics at the highest energy scales.
Search Wide, Aim High, Delve Deep: the Cosmic Frontier Strategy for DiscoveryThe Cosmic Frontier (CF) comprises a broad set of activities aimed at understanding the fundamental physics which governs the evolution of the Universe and its constituents. For Snowmass 2021, the CF is organized into topical groups, each of which produced a report summarizing the open questions and scientific opportunities in its area:• CF1 : particle-like dark matter [1];• CF2 : wave-like dark matter [2];• CF3 : cosmic probes of dark matter [3];• CF4 : dark energy and cosmic acceleration in the modern Universe [4];