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Model independent constraints on four-lepton operators

Adam Falkowski, Kin Mimouni

TL;DR

This paper provides a model-independent, flavor-agnostic analysis of dimension-6 lepton-sector operators in the SM EFT by separating leptonic vertex corrections from four-lepton interactions. It parametrize EFT effects with leptonic vertex corrections $\delta g$ and a complete set of lepton-only four-lepton operators, and performs a global fit to diverse data from LEP, W mass measurements, neutrino-electron scattering, parity-violating electron scattering, and muon/tau decays, yielding 68% CL intervals and a full correlation matrix. The results constrain 16 lepton-flavor-conserving four-lepton operators and translate into bounds on concrete leptophilic UV scenarios, including a leptophilic $Z'$, a vector triplet, and an inert Higgs, with typical scales of order a few TeV (and up to tens of TeV for strongly coupled states). The work highlights degeneracies and blind directions that could be resolved with polarized beams or future colliders, and establishes a versatile framework for recasting EFT constraints onto broad classes of beyond-Standard-Model theories.

Abstract

We obtain constraints on four-lepton interactions in the effective field theory with dimension-6 operators. To this end, we combine the experimental input from Z boson measurements in LEP-1, W boson mass and decays, muon and tau decays, lepton pair production in LEP-2, neutrino scattering on electrons, and parity violating electron scattering. The analysis does not rely on any assumptions about the flavor structure of the dimension-6 operators. Our main results are the confidence intervals for Wilson coefficients of 16 lepton-flavor conserving four-lepton operators, together with the full correlation matrix. Consequences for leptophilic models beyond the Standard Model are discussed.

Model independent constraints on four-lepton operators

TL;DR

This paper provides a model-independent, flavor-agnostic analysis of dimension-6 lepton-sector operators in the SM EFT by separating leptonic vertex corrections from four-lepton interactions. It parametrize EFT effects with leptonic vertex corrections and a complete set of lepton-only four-lepton operators, and performs a global fit to diverse data from LEP, W mass measurements, neutrino-electron scattering, parity-violating electron scattering, and muon/tau decays, yielding 68% CL intervals and a full correlation matrix. The results constrain 16 lepton-flavor-conserving four-lepton operators and translate into bounds on concrete leptophilic UV scenarios, including a leptophilic , a vector triplet, and an inert Higgs, with typical scales of order a few TeV (and up to tens of TeV for strongly coupled states). The work highlights degeneracies and blind directions that could be resolved with polarized beams or future colliders, and establishes a versatile framework for recasting EFT constraints onto broad classes of beyond-Standard-Model theories.

Abstract

We obtain constraints on four-lepton interactions in the effective field theory with dimension-6 operators. To this end, we combine the experimental input from Z boson measurements in LEP-1, W boson mass and decays, muon and tau decays, lepton pair production in LEP-2, neutrino scattering on electrons, and parity violating electron scattering. The analysis does not rely on any assumptions about the flavor structure of the dimension-6 operators. Our main results are the confidence intervals for Wilson coefficients of 16 lepton-flavor conserving four-lepton operators, together with the full correlation matrix. Consequences for leptophilic models beyond the Standard Model are discussed.

Paper Structure

This paper contains 22 sections, 42 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Formalism
  3. Experimental Input
  4. Z- and W-pole observables
  5. W mass
  6. Fermion pair production in LEP-2
  7. Low-energy neutrino scattering
  8. Parity violating electron scattering
  9. Tau and muon decays
  10. General Fit
  11. Leptophilic Models
  12. One by one
  13. Z prime
  14. Vector Triplet
  15. Inert Higgs
  16. ...and 7 more sections

Figures (3)

  • Figure 1: Summary of the 68% CL intervals for the Wilson coefficients of 4-lepton operators, assuming that only 1 such operator is present at a time and that leptonic vertex corrections are absent.
  • Figure 2: 95% CL lower limits on the scale suppressing 4-lepton operators in the EFT Lagrangian, assuming that only 1 such operator is present at a time and that leptonic vertex corrections are absent.
  • Figure 3: Left: 68 % CL (darker green) and 95 % CL (lighter green) regions for the ratio of the couplings over mass for the leptophilic Z' vector boson coupled to electrons only. Right: The same for Z' coupled universally to all leptons.