PHYSICS OF MIRROR FERMIONS

We review the theoretical motivation and phenomenological implications of mirror fermions. Mirror fermions are a new class of particles having V + A weak interactions. They are predicted by many recent particle theories, including orthogonal and unitary symmetries for family unification, Kaluza-Klein theories, extended supersymmetry and composite models. The mass of mirror particles breaks the electroweak symmetry and hence they must be lighter than about 300 GeV. Charged mirror leptons must be heavier than about 27 GeV. Mixing with ordinary quarks and leptons, the mirror fermions would cause violation of the V - A rule in weak interactions. We present an overall fit to experimental data and derive upper bounds for such mixing. We also make a survey of various laboratory experiments, as well as astrophysical and cosmological observations to find constraints for mirror neutrino masses, lifetimes and mixinf angles. We conclude that mirror neutrinos N with masses in the ranges mN ≲ 1 eV and mN ≳ 18 GeV could mix appreciably with ordinary neutrinos. In the ranges 50 MeV ≲ mN ≲ 18 GeV and 1 eV ≲ mN ≲ 25 eV the mixing is 10-4-10-8 or less. Elsewhere mirror neutrinos are forbidden by astrophysical or cosmological arguments. Mirror neutrinos with masses mN ≲ 25 eV or mN ≳ 5 GeV are WIMP candidates; to make them responsible also for the solar neutrino deficiency problem would be rather contrived, however. No limits can be inferred for mirror quarks which must have very small mixing with ordinary quarks. We describe the experimental signatures of and prospects for production of mirror fermions in the new generation of accelerators. © 1990.