photinos

Photino is the hypothetical fermionic superpartner of the photon in theories of supersymmetry. It would be a spin-1/2 neutral particle, and its interactions with ordinary matter arise from the electroweak gauge structure inherited from the photon and from mixing with other neutral superpartners after electroweak symmetry breaking.

In the minimal supersymmetric Standard Model (MSSM) the neutral fermions come from the superpartners of the B and W^0 gauge bosons (bino and wino) and from the two neutral higgsinos. These states mix to form four neutralinos, χ̃1^0–χ̃4^0. The photino itself is not generally an independent mass eigenstate; it appears as a component associated with the photon’s superpartner and contributes to the neutralino mixing, yielding physical neutralinos that are mixtures of bino, wino, and higgsinos.

Phenomenology: If R-parity is conserved, the lightest neutralino is typically stable and can be a dark matter candidate. Production of photino-like neutralinos would produce events with missing energy in collider experiments, since they interact weakly and would escape detectors. No conclusive evidence for photinos or any supersymmetric particle has been observed to date; collider and astrophysical searches have set limits on masses and couplings of neutralinos and other superpartners.

In summary, photinos are a component in the broader framework of supersymmetry, primarily understood as the photon’s superpartner that mixes to form the neutralinos—particles that remain central to experimental searches for supersymmetry and dark matter.