The Search for Feebly-Interacting Particles

TL;DR

This paper reviews the theoretical motivations and experimental efforts, especially accelerator-based, to discover feebly interacting particles at sub-GeV scales, which could explain dark matter and other fundamental physics mysteries.

Contribution

It provides a comprehensive overview of the current theoretical frameworks and experimental strategies for searching for feebly interacting particles at low mass scales.

Findings

Existing data may hint at FIPs presence.

Decadal experimental goals are outlined.

Systematic approaches guide current searches.

Abstract

At the dawn of a new decade, particle physics faces the challenge of explaining the mystery of dark matter, the origin of matter over antimatter in the Universe, the apparent fine-tuning of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV scale, but with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data may even provide hints of this possibility. Emboldened by the lessons of the LHC, a vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. We give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs, with special focus on accelerator-based experiments.