neutralinoshypothetical

Neutralinos are hypothetical fermions predicted by supersymmetric extensions of the Standard Model, most commonly the Minimal Supersymmetric Standard Model (MSSM). They arise as the mass eigenstates resulting from the mixing of the neutral gauginos (bino and wino) and the neutral higgsinos. There are four neutralinos, denoted χ̃_i^0 with i = 1 to 4, ordered by increasing mass. Each χ̃_i^0 is a linear combination of B̃, W̃^0, H̃_d^0 and H̃_u^0. Because they are Majorana fermions, a neutralino is its own antiparticle.

In models with R-parity conservation, the lightest neutralino χ̃_1^0 is stable and is a leading candidate for dark matter. Its relic abundance depends on its annihilation cross section in the early universe, influenced by its composition and by possible coannihilation with nearly degenerate superpartners and by resonant annihilation through heavy Higgs bosons. The neutralino’s couplings to Standard Model particles depend on the fraction that is bino, wino, or higgsino; this composition determines its interaction strengths and thus its detection prospects.

Production and detection methods span multiple experimental fronts. At colliders, neutralinos can be produced and appear in cascade decays, often yielding events with missing energy carried away by χ̃_1^0. In direct detection experiments, neutralinos may scatter elastically off nuclei, producing nuclear recoils via Higgs or Z exchange, with rates sensitive to the higgsino content. Indirect detection searches look for annihilation products such as gamma rays, positrons, or neutrinos from regions with high dark matter density.

Constraints on neutralino properties come from a combination of collider bounds, direct and indirect dark matter searches, and cosmological observations, collectively narrowing the viable parameter space in supersymmetric models.