Electroweakinos

Electroweakinos are the fermionic superpartners of the electroweak gauge and Higgs bosons in supersymmetric theories. In the Minimal Supersymmetric Standard Model (MSSM) these states arise from the bino (the superpartner of the U(1)Y gauge field), the wino (the superpartner of the SU(2)L gauge fields), and the two higgsinos (the superpartners of the Higgs doublets). After electroweak symmetry breaking these gaugino and higgsino states mix to form four neutralinos and two charginos, collectively called electroweakinos. The lightest neutralino is often the lightest supersymmetric particle (LSP) in R-parity conserving models and a candidate for dark matter; the heavier neutralinos and charginos can participate in cascades that end with the LSP.

In the MSSM the mass parameters M1, M2, and mu determine the neutralino and chargino spectra. The neutralino mass matrix is 4x4 and the chargino mass matrix is 2x2, with eigenstates chi^0_i (i = 1–4) and chi^±_i (i = 1–2). The composition of each state—whether bino-like, wino-like, or higgsino-like—controls its couplings, production rates, and decay patterns. In many models the spectrum is such that some electroweakinos are relatively light compared to colored superpartners.

Electroweakinos are primarily produced at colliders through electroweak interactions, and they decay through chains that end in the LSP, often yielding leptons, gauge bosons, or Higgs bosons and missing transverse energy. Scenarios with compressed mass spectra pose experimental challenges because decay products can be soft and missing energy small.

Constraints on electroweakinos come from LEP limits on chargino masses, LHC searches for multilepton plus missing energy signatures, and dark matter direct and indirect detection experiments. The exact limits depend on mass splittings and neutralino composition. In the NMSSM, a fifth neutralino from the singlino can mix with bino, wino, and higgsinos, altering the spectrum and phenomenology, but the term electroweakinos still refers to these weakly interacting gaugino–higgsino states.