[Paper Review] Anomalous magnetic moment of the muon in the two Higgs doublet model

E. O. İltan, H. Sundu|ArXiv.org|Mar 10, 2001

Computational Physics and Python Applications3 citations

TL;DR

This paper calculates new physics contributions to the muon anomalous magnetic moment (g-2) in the Type III Two Higgs Doublet Model (2HDM), including both scalar and pseudoscalar Higgs bosons. It derives a stringent upper bound of |ξ̄ₑᴺ,τμ| < 30 ± 5 GeV on the lepton-flavor-violating coupling, which is significantly tighter than bounds from the muon electric dipole moment, due to the sensitivity of g-2 to this coupling within current experimental uncertainty.

ABSTRACT

We calculate the new physics effects on the anomalous magnetic moment of the muon in the framework of the two Higgs doublet model. We predict an upper bound for the lepton flavor violating coupling, which is responsible for the point like interaction between muon and tau, by using the uncertainty in the experimental result of the muon anomalous magnetic moment. We show that the upper bound predicted is more stringent compared to the one which is obtained by using the experimental result of the muon electric dipole moment

Motivation & Objective

• To investigate new physics effects on the muon anomalous magnetic moment (AMM) in the Type III Two Higgs Doublet Model (2HDM).
• To derive a model-independent upper bound on the lepton-flavor-violating μ-τ coupling using the experimental uncertainty in the muon AMM measurement.
• To compare the resulting constraint with the bound derived from the muon electric dipole moment (EDM) limit.
• To assess the sensitivity of the AMM to internal μ-lepton and e-lepton contributions, and justify their neglect in the analysis.

Proposed method

• The calculation is performed at one-loop level, including contributions from both neutral Higgs bosons h⁰ and A⁰, with internal μ and τ leptons as propagators.
• The model assumes tree-level flavor-changing neutral currents (FCNC) in the leptonic sector via complex Yukawa couplings ξ̄ₑᴺ,τμ.
• Theoretical expressions for the new physics contribution to the muon AMM are derived using the general 2HDM Lagrangian and the parametrization of the Higgs potential.
• The bound on |ξ̄ₑᴺ,τμ| is determined by requiring that the new physics contribution Δaμ,New does not exceed the current experimental uncertainty of ~1–2×10⁻⁹.
• The analysis includes a comparison with the EDM constraint from the 95% CL limit dμ < 10.34×10⁻¹⁹ e·cm.
• Numerical results are presented via plots showing dependence on |ξ̄ₑᴺ,τμ|, sinθτμ, and Higgs masses, with sensitivity analysis on μ-lepton coupling.

Experimental results

Research questions

• RQ1 What is the upper bound on the μ-τ lepton-flavor-violating coupling in the Type III 2HDM, derived from the experimental uncertainty in the muon anomalous magnetic moment?
• RQ2 How does this bound compare to the one obtained from the muon electric dipole moment constraint?
• RQ3 To what extent is the muon AMM sensitive to the internal μ-lepton contribution in the 2HDM?
• RQ4 How do the masses of the neutral Higgs bosons h⁰ and A⁰ affect the new physics contribution to the muon AMM?
• RQ5 Can the complex phase in the μ-τ Yukawa coupling be constrained more stringently via g-2 than via EDM measurements?

Key findings

• The upper bound on the μ-τ flavor-violating coupling |ξ̄ₑᴺ,τμ| is predicted to be less than 30 ± 5 GeV, based on the assumption that new physics contributions to the muon AMM must not exceed the current experimental uncertainty of ~1–2×10⁻⁹.
• This bound is significantly more stringent than the one derived from the muon electric dipole moment limit, which gives an upper bound of ~10³ GeV.
• The new physics contribution to the muon AMM increases with |ξ̄ₑᴺ,τμ| and exceeds the experimental uncertainty for couplings above ~30 GeV.
• The contribution to the muon AMM is weakly sensitive to the μ-μ Yukawa coupling, justifying its neglect in the analysis for |ξ̄ₑᴺ,μμ| < 0.1 GeV.
• The AMM contribution decreases with increasing Higgs mass mₕ⁰, indicating that heavier Higgs bosons suppress the new physics effect.
• The dependence on the CP-violating phase sinθτμ shows that larger values of sinθτμ reduce the contribution, helping to keep it within the experimental uncertainty.