Levions

Levions are a hypothetical class of gauge bosons proposed in certain extensions of the Standard Model to mediate a putative fifth fundamental interaction or to connect the visible sector with a hidden or dark sector. The term is used in theoretical discussions to describe neutral, weakly interacting vector particles whose existence would indicate new physics beyond the Standard Model. The name is often associated with notions of lightness or levitation, reflecting their proposed small couplings and subtle effects.

In common theoretical frameworks, levions are envisioned as neutral spin-1 bosons with masses that can vary widely depending on the model. They may couple to Standard Model fields through portal interactions, such as kinetic mixing with the photon (vector portal) or interactions tied to the Higgs sector. Depending on the scenario, levions can be stable on cosmological timescales or decay into Standard Model particles like leptons or hadrons. Their production could occur in high-energy collisions, meson decays, or as remnants from early-universe processes, and their signatures range from missing energy events to displaced decays.

Experimental status remains inconclusive. No confirmed detections of levions have been reported, and a variety of collider, fixed-target, and astrophysical searches have constrained portions of their possible parameter space. If they exist, levions could have implications for dark matter models, cosmology, or short-range modifications of gravity. They are also a common feature in discussions of hidden-sector dynamics and physics beyond the Standard Model.

See also: dark photon, hidden sector, fifth force, axion-like particle.