Sneutrinos

In supersymmetric theories, the sneutrino is the scalar superpartner of the neutrino. Each neutrino flavor has a corresponding scalar field obtained by applying SUSY to the lepton doublet. The sneutrino is a spin-0 particle and, like other superpartners, is part of a supermultiplet containing the Standard Model lepton and its fermionic partner.

In the minimal supersymmetric standard model (MSSM), the sneutrino is typically the scalar partner of the left-handed neutrino, denoted \tilde{\nu}_L. If right-handed neutrinos are included, their scalar partners \tilde{\nu}_R may also appear. The sneutrino states can mix, but the left-right mixing is usually suppressed by the small neutrino Yukawa couplings, so the mass eigenstates are often predominantly left-handed or right-handed sneutrinos.

Sneutrinos interact via the weak force through their left-handed component, and they couple to Higgs and neutralinos. They carry lepton number and are neutral electrically. The masses arise from soft SUSY-breaking terms and, in extended models, from Higgs vacuum expectation values and neutrino Yukawa interactions; the spectrum can split into CP-even and CP-odd states depending on model content.

As dark matter candidates, left-handed sneutrinos are disfavored in simple models because their Z-boson–mediated interactions lead to elastic scattering rates that exceed experimental limits. Right-handed or singlet sneutrinos can be viable if their couplings to the Z boson are suppressed, yielding the right relic abundance and direct-detection properties.

Experimentally, sneutrinos have not been observed. Collider searches at the Large Hadron Collider and previous experiments constrain their masses and decay patterns within various SUSY scenarios. If produced, sneutrinos would contribute to missing energy signatures alongside other SUSY particles.