Bounds on charged lepton mixing with exotic charged leptons

Abstract

We examine the effects of mixing induced light heavy charged lepton neutral currents on the partial wave amplitude for the process l⁺l⁻ →ZZ (withl = e,μ or τ). By imposing the constraints that the amplitude should not exceed the perturbative unitarity limit at high energy (√s = Λ), we obtain bounds on light heavy charged lepton mixing parameter sin²(2θ ^a_L ) where θ ^a_L is the mixing angle of the ordinary charged lepton with its exotic partner. For Λ = 1 TeV, no bound is obtained on sin² (2θ ^a_L ) form _E < 0.69 TeV. However, sin² (2θ ^a_L ) ≤ 1.52×10⁻⁵ form _E = 5 TeV, sin² (2θ ^a_L ) ≤ 2.41 ×10⁻⁷ form _E = 10 TeV. Similarity for Λ = ∞ no bound is obtained on sin² (2θ ^a_L ) for m_E < 1.97 TeV and sin² (2θ ^a_L ) ≤ 0.15 form _E = 5 TeV and sin² (2θ ^a_L ) ≤ 3.88×10^-2 form _E = 10 TeV.