Abstract
Standard Model may allow an extended gauge sector with anomaly-free flavored gauge symmetries, such as Li −Lj , Bi −Lj , and B −3Li, where i, j = 1, 2, 3 are flavor indices. We investigate phenomenological implications of the new flavored gauge boson Z′ in the above three classes of gauge symmetries. Focusing on the gauge boson mass above 5 GeV, we use the lepton universality test in the Z and τ /μ decays, LEP searches, LHC searches, neutrino trident production bound, and LHC Z → 4μ searches to put constraints on the g′ −MZ′ plane. When L1 is involved, the LEP bounds on the e−e+ → ℓ−ℓ+ processes give the most stringent bounds, while the LHC bound becomes the strongest constraints in the large {M}_{Z^{prime }} region when Bi is involved. The bound from Z → 4μ productions, which is applicable for L2-involved scenarios, provides stringent bounds in the small {M}_{Z^{prime }} region. One exception is the B − 3L2 scenario, in which case only a small region is favored due to the lepton universality.
Highlights
Universality in the Z and τ /μ decays
When L1 is involved, the LEP bounds on the e−e+ → − + processes give the most stringent bounds, while the LHC bound becomes the strongest constraints in the large MZ region when Bi is involved
Bounds on g and MZ for the Li − Lj models come from the LEP search [18], HFAG lepton universality test [16], and SLD/LEP Z-decay lepton universality test [15], respectively represented in figure 1 as dashed red, dotted blue, and solid black curves
Summary
Let us consider flavored gauge symmetries under which the left-handed and right-handed fermions (quarks and leptons) transform equivalently, and the SM gauge invariance extended to SU(2)L × SU(2)R is respected. Where i contains the i-th generation of the SU(2)L doublet (νL, eL) and SU(2)R doublet (νR, eR) The latter includes the right-handed neutrino νR which can get a Majorana mass after the Li − Lj symmetry breaking. A typical difficulty with such a flavored gauge symmetry is generation of the observed lepton (quark) mixing, which may require a judicial choice of the Higgs sector [8, 14]. One can write down the B − 3Li gauge interaction Lagrangian, LBin−t 3Li. where qj represents the j-th generation of the left- and right-handed quark doublet.
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