Light weakly coupled axial forces: models, constraints, and projections

  • Yonatan Kahn
  • Gordan Krnjaic
  • Siddharth Mishra-Sharma
  • Tim M. P. Tait
Open Access
Regular Article - Theoretical Physics


We investigate the landscape of constraints on MeV-GeV scale, hidden U(1) forces with nonzero axial-vector couplings to Standard Model fermions. While the purely vector-coupled dark photon, which may arise from kinetic mixing, is a well-motivated scenario, several MeV-scale anomalies motivate a theory with axial couplings which can be UV-completed consistent with Standard Model gauge invariance. Moreover, existing constraints on dark photons depend on products of various combinations of axial and vector couplings, making it difficult to isolate the effects of axial couplings for particular flavors of SM fermions. We present a representative renormalizable, UV-complete model of a dark photon with adjustable axial and vector couplings, discuss its general features, and show how some UV constraints may be relaxed in a model with nonrenormalizable Yukawa couplings at the expense of fine-tuning. We survey the existing parameter space and the projected reach of planned experiments, briefly commenting on the relevance of the allowed parameter space to low-energy anomalies in π0 and 8Be decay.


Beyond Standard Model Gauge Symmetry 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


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Copyright information

© The Author(s) 2017

Authors and Affiliations

  • Yonatan Kahn
    • 1
  • Gordan Krnjaic
    • 2
  • Siddharth Mishra-Sharma
    • 1
  • Tim M. P. Tait
    • 3
  1. 1.Princeton UniversityPrincetonU.S.A.
  2. 2.Fermi National Accelerator LaboratoryBataviaU.S.A.
  3. 3.University of California, IrvineIrvineU.S.A.

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