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Constraints on a light leptophilic scalar from dark-sector couplings

Marco Graziani1,*, Giacomo Landini2,†, Federico Mescia2,‡, Claudio Toni3,§, and Ludovico Vittorio1,∥

  • *Contact author: graziani.1962894@studenti.uniroma1.it
  • †Contact author: giacomo.landini@lnf.infn.it
  • ‡Contact author: federico.mescia@lnf.infn.it
  • §Contact author: claudio.toni@lapth.cnrs.fr
  • ∥Contact author: ludovico.vittorio@uniroma1.it
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Phys. Rev. D 114, 095014 – Published 9 November, 2026

DOI: https://doi.org/10.1103/5853-6d3f

Abstract

We study a minimal framework where a Majorana fermion dark matter particle interacts with a light scalar mediator coupled mainly to electrons. We examine both freeze-out and freeze-in production to determine the regions of parameter space that yield the correct relic abundance with particular emphasis on a detailed comparison with results in the recent literature. The analysis includes cosmological and astrophysical constraints as well as laboratory bounds from electron-recoil experiments, fixed target searches, and precision measurements. The combined results identify a narrow but viable parameter region, favoring sub-GeV dark matter, and define clear targets for future experimental tests. This highlights the strong complementarity between direct-detection experiments and collider searches. We additionally investigate the mediator-mass region around 17 MeV, motivated by the hints reported by the ATOMKI experiment and the PADME collaboration, including couplings between the mediator and light quarks. Direct searches already constrain a large region of the parameter space, even when dark matter is produced via freeze-in, pointing again to sub-GeV dark matter.

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Phys. Rev. D 114, 095014– Published 9 November, 2026
  • Received 6 June 2026
  • Accepted 23 September 2026
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