The Possibility of New Fermions With $\Delta$ I = 0 Mass

In the Glashow-Weinberg-Salam model the fermions have ΔI = 1 2 masses from the breaking of the weak SU(2) gauge symmetry. In many enlarged models, such as those from grand unified and/or supersymmetric theories, there are additional fermions with undetermined ΔI = 0 (SU(2) invariant) masses. We study these new fermions. They induce flavour changing neutral currents. We show that the mixing angles of ΔI = 0 fermions of mass order M with normal ΔI = 1 2 fermions of mass order m ⪡ M are order η or η 2 , where η = m / M . If M > 150 δ , δ being a model-dependent mixing parameter of order a normal fermion mass, the amplitudes of all FCNC processes are below the experimental sizes and limits. Thus for δ ⪅0.1 GeV, M can be as low as 20 GeV, close to the present experimental lower bound. δ is fixed, and less than 0.1 GeV for all relevant cases, if we assume the mass hierarchy of the known fermions is not the result of a particular choice of ΔI = 0 mass parameters. If produced ΔI = 0 mass fermions will be noticeable by the mass degeneracy within their isospin multiplets. There will be an enhanced ratio of neutral to charged decays over the normal fermions. Standard GUT predictions are changed little.

GRAND UNIFIED THEORY: SU(5)
FERMION: POSTULATED PARTICLE
FERMION: MASS
MASS: FERMION
MULTIPLET: MIXING ANGLE
MIXING ANGLE: MULTIPLET
SUPERSYMMETRY
ISOSPIN
LEPTON NUMBER: VIOLATION
NEUTRAL CURRENT: FLAVOR CHANGING

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The Possibility of New Fermions With Δ\DeltaΔ I = 0 Mass

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The Possibility of New Fermions With $\Delta$ I = 0 Mass