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Constraints on dark axion portal: Missing energy and fermion EDMs

Sergei N. Gninenko1,2,3, N. V. Krasnikov1,2, Valery E. Lyubovitskij4,3, Sergey Kuleshov3,5, Alexey S. Zhevlakov2,6, I. V. Voronchikhin1,7, and D. V. Kirpichnikov1,*

  • *Contact author: dmbrick@gmail.com
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Phys. Rev. D 113, 095028 – Published 19 May, 2026

DOI: https://doi.org/10.1103/2yms-pk6p

Abstract

We study a model in which a new interactions between the Standard Model (SM) photon and both the dark photon (γD) and an axionlike particles (ALP or a) are described by the dark axion portal operator. The implications of this dark axion portal scenario for electron fixed-target experiments are presented. In particular, we investigate the missing energy signatures associated with production of dark photons and their subsequent invisible decays into stable dark sector fermions, γD→χχ¯. We discuss the discovery potential for such a scenario and derive projected sensitivity curves for the NA64e and LDMX experiments. Furthermore, novel constraints of the NA64e for 9.37×1011 electrons on target are derived by considering two production mechanisms for invisible states: (i) the bremsstrahlung-like emission of an aγD pair, eN→eNγ*(→aγD), and (ii) the exclusive vector meson photoproduction, γ*N→NV, followed by the invisible decays of vector mesons, V→aγD. Additionally, the constraints on the parameter space of CP-violating, fermion-specific ALP and dark photon couplings are established. These constraints are derived from current experimental bounds on the electric dipole moments (EDMs) of SM fermions, incorporating loop-induced contributions to the EDMs of the electron, muon, and neutron.

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Phys. Rev. D 113, 095028– Published 19 May, 2026
  • Received 17 February 2026
  • Accepted 21 April 2026
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