New gauge bosonZ′and lepton flavor violating decays and production of vector mesons

Abstract

Considering the constraints on the lepton flavor violating (LFV) couplings of the new gauge boson Z ′ to ordinary leptons from the experimental upper limit for the LFV process ℓ → 3ℓ ′ , we calculate the contributions of Z ′ to the LFV decays V → ℓ i ℓ j with V ∈ {φ, J/Ψ, Ψ(2S), Υ (n) } and τ → µ(e)φ in the context of several Z ′ models. We find that all Z ′ models considered in this paper can produce significant contributions to these decay processes and make the value of the branching ratio Br(τ → eφ) above its experimental upper limit. The experimental upper limit of τ → eφ can give more severe constraints on these Z ′ models than those given by the rare decay process τ → 3e.

Palatable leptoquark scenarios for lepton flavor violation in exclusive b → sℓ 1 ℓ 2 modes

“…Like in the previous case, the branching ratio B(B → Kµτ ) can be between zero and O(10 −6 ) even if R νν = 1 and B(B s → τ τ ) exp = B(B s → τ τ ) SM , but it is stricly non-zero for R νν > 1. This model too is experimentally verifiable: (i) it leads to R K * = 0.86 (12), thus R K * < 1 [67], and (ii) it can be ruled out if R νν < 1 and/or B(B s → τ τ ) 10 −5 .…”

“…In fact, the couplings of ∆ (1/3) to the muon, which are necessary to get R K < 1, are large enough and push R D to values smaller than the SM one. 9 Furthermore, even though we were able to find points that give acceptable values for 9 In obtaining RD we used the B → D form factors recently computed in lattice QCD [74], which also give R SM D = 0.286 (12). [46] it was even argued that such a deviation from lepton flavor universality cannot be larger than 2%.…”

“…Thus in the U 3 -model we vary the couplings within |x LL ij | < 4π and apply the abovementioned constraints, namely the one on C µµ 9 , and the one arising from R exp D , both at 2σ. 12 We fix the mass at m U = 1 TeV. Further constraints are coming from the purely thirdgeneration charged current and the up-type neutral current processes which are mediated by the U (5/3) 3µ eigencharge component.…”

“…Furthermore, we have checked that the LFU ratios, Γ(τ → Kν)/Γ(K → µν) and Γ(K → µν)/Γ(K → eν), are consistent with experiment. 12 To explain R Like in the previous subsection, with the couplings selected to verify the above constraints, we can compute various quantities. In particular, in figure 5 we show the correlation between R νν and B(B s → τ τ ), and again observe that the current experimental limit on R νν provides a stringent constraint on the parameter space.…”

“…Theoretically, the LFV decays are predicted in various NP scenarios, such as in models with heavy sterile fermions [1][2][3][4][5][6], in models with a peculiar breaking of supersymmetry [7][8][9][10], in models involving an extra Z -boson [11,12], and in multiple scenarios founded on the paradigm of existence of one or more leptoquark (LQ) states [13]. Most of the current experimental efforts in searching for the effects of LFV are focused onto lepton decays, 1 → 2 γ, 1 → 3 2 (with 1,2 ∈ {e, µ, τ }), and on the µ − e conversion in nuclei [14].…”