Light new particles generate asymmetries in e+e- to tau+tau- that allow model-dependent constraints on tau dipole moments, including non-zero effects without electron polarization via imaginary parts.
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Testing new physics with the electron g-2
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abstract
We argue that the anomalous magnetic moment of the electron (a_e) can be used to probe new physics. We show that the present bound on new-physics contributions to a_e is 8*10^-13, but the sensitivity can be improved by about an order of magnitude with new measurements of a_e and more refined determinations of alpha in atomic-physics experiments. Tests on new-physics effects in a_e can play a crucial role in the interpretation of the observed discrepancy in the anomalous magnetic moment of the muon (a_mu). In a large class of models, new contributions to magnetic moments scale with the square of lepton masses and thus the anomaly in a_mu suggests a new-physics effect in a_e of (0.7 +- 0.2)*10^-13. We also present examples of new-physics theories in which this scaling is violated and larger effects in a_e are expected. In such models the value of a_e is correlated with specific predictions for processes with violation of lepton number or lepton universality, and with the electric dipole moment of the electron.
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This work provides a comprehensive analysis of light new physics contributions to tau lepton dipole moments, detailing interpretations of asymmetry measurements for spin-0 and spin-1 bosons, their decoupling to the EFT limit, and a case study of a tauphilic vector boson at Belle II.
Z-boson exchange contributes ~3e-6 to the relevant asymmetries while four-fermion operators can reach ~1e-5 times Wilson coefficients, with loop insertions offering an additional path to a_tau without beam polarization.
Future lepton colliders can improve existing constraints on the tau lepton's dipole moments by several orders of magnitude through complementary channels.
The paper surveys theoretical motivations, experimental searches, and bounds on the dark photon as a kinetically mixed gauge boson from a dark sector, covering both massive and massless cases along with related milli-charged fermion constraints.
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Light new physics and the $\tau$ lepton dipole moments: prospects at Belle II
Light new particles generate asymmetries in e+e- to tau+tau- that allow model-dependent constraints on tau dipole moments, including non-zero effects without electron polarization via imaginary parts.
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Light new physics and the $\tau$ lepton dipole moments
This work provides a comprehensive analysis of light new physics contributions to tau lepton dipole moments, detailing interpretations of asymmetry measurements for spin-0 and spin-1 bosons, their decoupling to the EFT limit, and a case study of a tauphilic vector boson at Belle II.
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Four-fermion operators, $Z$-boson exchange, and $\tau$ lepton dipole moments
Z-boson exchange contributes ~3e-6 to the relevant asymmetries while four-fermion operators can reach ~1e-5 times Wilson coefficients, with loop insertions offering an additional path to a_tau without beam polarization.
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Probing $\tau$ lepton dipole moments at future Lepton Colliders
Future lepton colliders can improve existing constraints on the tau lepton's dipole moments by several orders of magnitude through complementary channels.
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The Dark Photon
The paper surveys theoretical motivations, experimental searches, and bounds on the dark photon as a kinetically mixed gauge boson from a dark sector, covering both massive and massless cases along with related milli-charged fermion constraints.