Broken Supersymmetric U(1) Gauge Factor at the TeV Scale

The appearance of a broken supersymmetric U(1) gauge factor at the TeV scale is relevant for several reasons. If it truly exists, then one important consequence is that at the 100 GeV energy scale, the two-doublet Higgs structure is of a more general form than that of the Minimal Supersymmetric Standard Model (MSSM). This is a prime example of tree-level nondecoupling. Furthermore, a particular U(1)N from the superstring-inspired E6 model allows for the existence of naturally light singlet neutrinos which may be necessary to accommodate the totality of neutrino-oscillation experiments. To appear in Proc. of the Third International Workshop on Particle Physics Phenomenology, Chin Shan, Taiwan (November, 1996) 1 Why Supersymmetric U(1)? Consider the top-down approach. Start with the E8×E8 heterotic string, which compactifies to the E6 superstring,[1] which is then broken by flux loops transforming as the adjoint 78 representation. Under SU(3)C × SU(3)L × SU(3)R, 78 = (3, 3, 3) + (3, 3, 3) + (8, 1, 1) + (1, 8, 1) + (1, 1, 8). (1) Now (1,8,1) can be used for SU(3)L → SU(2)L×U(1)YL and (1,1,8) for SU(3)R → U(1)T3R+YR so that the correct Q = T3L+YL+T3R+YR is obtained, hence U(1)YL ×U(1)T3R+YR remains unbroken and can be rewritten as U(1)Y × U(1)η. The extra U(1)η presumably survives[2] down to the TeV energy scale where it is broken together with the supersymmetry. Consider also the bottom-up approach. Start with a possible experimental clue, such as the Rb ≡ (Z → bb̄/Z → hadrons) excess. Look for an U(1) explanation, and remarkably U(1)η is also found.[3] Another possible clue is the totality of neutrino-oscillation experiments (solar, atmospheric, and laboratory) which suggest that there are at least 4 neutrinos. Details of how this is related to an extra U(1) will be presented later. 2 Tree-Level Nondecoupling at the 100 GeV Scale As the U(1) gauge factor is broken together with the supersymmetry at the TeV scale, the resulting heavy scalar particles have nondecoupling contributions to the interactions of the light scalar particles.[4] Consequently, the two-doublet Higgs structure is of a more general form than that of the MSSM. Previous specific examples have been given.[5] Here I present the most general analysis.[6] Let