Dark Sectors and New, Light, Weakly-Coupled Particles

TL;DR

Dark sectors comprise new, light, weakly-coupled particles that could explain dark matter and solve outstanding physics puzzles, with diverse experimental opportunities using existing facilities for potential groundbreaking discoveries.

Contribution

This review summarizes the motivation, theoretical models, and experimental prospects for dark sectors and light weakly-coupled particles, highlighting opportunities for discovery at the intensity frontier.

Findings

Dark sectors include axions, dark photons, and sub-GeV dark matter.

Existing facilities can explore dark sector particles with modest experiments.

Potential for game-changing discoveries in particle physics and cosmology.

Abstract

Dark sectors, consisting of new, light, weakly-coupled particles that do not interact with the known strong, weak, or electromagnetic forces, are a particularly compelling possibility for new physics. Nature may contain numerous dark sectors, each with their own beautiful structure, distinct particles, and forces. This review summarizes the physics motivation for dark sectors and the exciting opportunities for experimental exploration. It is the summary of the Intensity Frontier subgroup "New, Light, Weakly-coupled Particles" of the Community Summer Study 2013 (Snowmass). We discuss axions, which solve the strong CP problem and are an excellent dark matter candidate, and their generalization to axion-like particles. We also review dark photons and other dark-sector particles, including sub-GeV dark matter, which are theoretically natural, provide for dark matter candidates or new dark matter interactions, and could resolve outstanding puzzles in particle and astro-particle physics. In many cases, the exploration of dark sectors can proceed with existing facilities and comparatively modest experiments. A rich, diverse, and low-cost experimental program has been identified that has the potential for one or more game-changing discoveries. These physics opportunities should be vigorously pursued in the US and elsewhere.