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Vectorlike lepton imprints at lepton $g-2$ measurements and $e^+e^-$ colliders

Sang Quang Dinh, Hieu Minh Tran

Abstract

A fermion can be chiral or vectorlike with respect to a given symmetry, depending on its coupling to the corresponding gauge boson. Vectorlike fermions have a distinct property that their left-handed and right-handed components behave in the same way under the gauge symmetry. In this paper, we investigate an extension of the standard model with an $SU(2)$ doublet of vectorlike leptons and two complex scalars. The new physics effects on the lepton anomalous magnetic moment, as well as the electron and muon pair production processes at $e^+e^-$ colliders are analyzed. Taking into account the updated measurement results of the electron and muon $g-2$, the LEP and the LHC data, the viable parameter space of the model is identified. We also examine the prospect of testing the model using $μ^+μ^-$ signals from electron-position annihilation at the Future Circular Collider (FCC-ee). The analysis shows that the FCC-ee will be able to exclude a significant part of the parameter space, pinpointing exiguous viable regions to be tested in the future due to its high precision.

Vectorlike lepton imprints at lepton $g-2$ measurements and $e^+e^-$ colliders

Abstract

A fermion can be chiral or vectorlike with respect to a given symmetry, depending on its coupling to the corresponding gauge boson. Vectorlike fermions have a distinct property that their left-handed and right-handed components behave in the same way under the gauge symmetry. In this paper, we investigate an extension of the standard model with an doublet of vectorlike leptons and two complex scalars. The new physics effects on the lepton anomalous magnetic moment, as well as the electron and muon pair production processes at colliders are analyzed. Taking into account the updated measurement results of the electron and muon , the LEP and the LHC data, the viable parameter space of the model is identified. We also examine the prospect of testing the model using signals from electron-position annihilation at the Future Circular Collider (FCC-ee). The analysis shows that the FCC-ee will be able to exclude a significant part of the parameter space, pinpointing exiguous viable regions to be tested in the future due to its high precision.

Paper Structure

This paper contains 15 sections, 25 equations, 24 figures.

Table of Contents

  1. Introduction
  2. Model setup
  3. New physics imprints of the model
  4. Lepton anomalous magnetic moments
  5. Lepton pair productions at $e^+e^-$ colliders
  6. Numerical analysis
  7. Benchmark investigation
  8. a. Constraints on $(m_L, m_{\chi_r})$ plane
  9. b. Constraints on $(y_e, y_\mu)$ plane
  10. c. Constraints on $(m_L,y_e)$ plane
  11. d. Constraints on $(m_L,y_\mu)$ plane
  12. e. Constraints on $(m_{\chi_r}, y_e)$ plane
  13. f. Constraints on $(m_{\chi_r}, y_\mu)$ plane
  14. Global investigation
  15. Conclusions

Figures (24)

  • Figure 1: New physics contribution to lepton anomalous magnetic moment at the leading order.
  • Figure 2: Feynman diagrams for the leading new physics contributions to the cross section of $e^+e^- \rightarrow e^+e^-$.
  • Figure 3: Feynman diagrams for the leading new physics contributions to the cross section of $e^+e^- \rightarrow \mu^+\mu^-$.
  • Figure 4: The LHC constraint on $(m_L,m_{\chi_r})$ plane. Assuming BR($E^\pm \rightarrow \ell^\pm +\chi_r$)=100%, the blue and the red regions would be excluded at 95% confident level by the ATLAS ATLAS:2024lda and the CMS CMS:2024wzb experiments, respectively. The yellow region satisfies the condition $m_{\chi_r}<m_L<m_{\chi_i}$ in the case $\delta=1$.
  • Figure 5: Constraints on $(m_L, m_{\chi_r})$ plane for $y_e=1.3$ and $y_\mu=0.12$. Dotted and blue hatch regions: allowed by the constraints (\ref{['delta-ae']}) (\ref{['sigma-ee']}) on $\Delta a_e$ and $\sigma(e^+e^- \rightarrow e^+e^-)$. Green, pink, and yellow regions: excluded by the constraint (\ref{['AFB-ee']}) on $A_{FB}(e^+e^-\rightarrow e^+e^-)$, the LHC search (Figure \ref{['LHC']}) and the LEP data (\ref{['LEPmass']}).
  • ...and 19 more figures