TY - JOUR
T1 - The possibility of new fermions with ΔI = 0 mass
AU - Del Aguila, F.
AU - Bowick, M. J.
N1 - Funding Information:
* Work supported in part by the US Department of Energy under Contract No. DE-AS-05-81-ER40008. 1 Present address: Department de Fisica Teorica, Universitat Autonoma de Barcelona, Bellaterra (Barcelona), Spain. 2 Address after 1 September 1983, Physics Department, Yale University, New Haven, Connecticut 06520.
Funding Information:
We have had many enlightening discussions with P. Ramond and thank him for his advice. We also thank M.K. Chase, P. Sikivie and H. Georgi for their comments and the anonymous referee for suggesting a simpler derivation of the mixing angle theorems. F.A. acknowledges the US-Spanish Joint Committee for Scientific and Technological Cooperation for the award of a fellowship and thanks the Particle Physics Group of the University of Florida for its hospitality.
PY - 1983/8/29
Y1 - 1983/8/29
N2 - 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 η2, 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{less-than or approximate}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.
AB - 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 η2, 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{less-than or approximate}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.
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U2 - 10.1016/0550-3213(83)90316-4
DO - 10.1016/0550-3213(83)90316-4
M3 - Article
AN - SCOPUS:25744433950
SN - 0550-3213
VL - 224
SP - 107
EP - 136
JO - Nuclear Physics, Section B
JF - Nuclear Physics, Section B
IS - 1
ER -