Feebly-interacting particles: FIPs 2022 Workshop Report

Abstract

Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, 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, or even radically below, down to sub-eV scales, and 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 provide numerous hints for such possibility. 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. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.

Dark sector searches at dump experiments

“…The attractiveness of this physics case arises, among other reasons, because "light" Dark Matter (DM) interactions with Standard Model fields could proceed via new light mediators in order to reproduce the observed DM relic abundance. There is a number of models (and benchmark cases) that can be defined that are motivated by minimal extensions of Standard Model (SM) [1,2]. An example of the parameter space of such a benchmark scenario is shown in Figure 1, displaying the status of current exclusions for a Heavy Neutral Lepton (HNL) with predominant muon-coupling (so-called BC7 scenario in the CERN-PBC benchmark cases, see for example [3] and references therein.…”

Standard and Non-Standard Aspects of Neutrino Physics

“…The absence of evidence thus far imposes constraints on the mixing for masses ranging from the eV to the PeV scale, with additional bounds from cosmology and astrophysics [132][133][134]. Further experiments are planned and proposed for the future with the aim to probe the relevant parameter space more deeply (see, e.g., the reports [135][136][137]). Also, future discussed colliders [138][139][140][141] have the potential to discover heavy Majorana neutrinos in the mass range from a few GeV to tens of TeV.…”

Improved constraints for axion-like particles from 3-photon events at $$e^+e^-$$ colliders

“…During the past few years there is a noticeable increase of interest in the MeV to GeV range [14][15][16][17][18]. Although significant progress has been made recently [19,20], there still remain untested regions in the parameter space, especially when compared to the low-mass region where astrophysical constraints can be applied.…”