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Flavor specific chiral U(1)X framework for explaining the ATOMKI anomaly

Aditya Batra1,*, F. R. Joaquim1,†, Hemant Prajapati2,‡, and Rahul Srivastava2,§

  • *Contact author: aditya.batra@tecnico.ulisboa.pt
  • †Contact author: filipe.joaquim@tecnico.ulisboa.pt
  • ‡Contact author: hemant19@iiserb.ac.in
  • §Contact author: rahul@iiserb.ac.in
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Phys. Rev. D 114, 015042 – Published 27 July, 2026

DOI: https://doi.org/10.1103/j8xh-hrpj

Abstract

Recent anomalies in nuclear transitions observed by the ATOMKI Collaboration suggest the existence of a new boson with a mass of ∼17  MeV. A theoretically consistent interpretation requires a framework that not only matches the kinematics but also reproduces the observed decay rates while satisfying stringent experimental constraints. Among various possibilities, an axial-vector or mixed vector–axial-vector mediator Z′ emerges as the most viable candidate. However, getting such couplings for a light Z′ gauge boson is a highly nontrivial task. In this work, we construct a gauged chiral, flavor specific U(1)X extensions of the Standard Model where the associated Z′ boson acts as the 17 MeV particle. By employing a two Higgs doublet framework, we generate the necessary nonvanishing axial-vector couplings while ensuring gauge anomaly cancellation and consistent fermion mass generation. Focusing on the Be8 and He4 signals, we show that in this model the viable parameter space to resolve the ATOMKI anomalies is also consistent with a diverse set of experimental constraints, including atomic parity violation, beam dump experiments, meson decays, and neutrino nucleus and neutrino electron scatterings. Our results demonstrate that this framework offers a theoretically sound and phenomenologically robust solution to the ATOMKI anomaly.

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Phys. Rev. D 114, 015042– Published 27 July, 2026
  • Received 30 April 2026
  • Accepted 26 June 2026
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