Feebly interacting particle

Feebly interacting particles (FIPs) are subatomic particles defined by having extremely suppressed interactions with the Standard Model (SM) bosons and / or fermions. These particles are potential thermal dark matter candidates, extending the model of weakly interacting massive particles (WIMPs) to include weakly interacting sub-eV particles (WISPs) and others. FIP physics is also known as dark-sector physics.^[1]

Candidates

FIP candidates could be massive (FIMP / WIMP) or massless and coupled to the SM particles through some minimal coupling strength.^[1] The light FIPs are theorized to be dark matter candidates, and, they provide an explanation for the origin of neutrino masses and CP symmetry in strong interactions.^[2]

Neutrinos technically qualify as FIPs, but usually when the acronym "FIP" is used, it is intended to refer to some other, as-yet unknown particle. Cai, Cacciapaglia, and Lee (2022)^[3] proposed massive gravitons as feebly Interacting particle candidates.^[3][4]

See also

• WIMP – weakly interacting massive particle
• WISP – weakly interacting sub-eV / slight / slender particle