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Combined constraints on dark photons from high-energy collisions, cosmology, and astrophysics

A. W. Romero Jorge ^1,2,3,*, L. Sagunski ², Guan-Wen Yuan ^4,5, T. Song ⁶, and E. Bratkovskaya^6,2,3

¹Frankfurt Institute for Advanced Studies (FIAS), Ruth Moufang Straße 1, 60438 Frankfurt, Germany
²Institut für Theoretische Physik, Johann Wolfgang Goethe University, Max-von-Laue-Straße 1, 60438 Frankfurt, Germany
³Helmholtz Research Academy Hessen for FAIR (HFHF), GSI Helmholtz Center for Heavy Ion Physics, Campus Frankfurt, 60438 Frankfurt, Germany
⁴Department of Physics, University of Trento, Via Sommarive 14, 38123 Povo (TN), Italy
⁵Trento Institute for Fundamental Physics and Applications (TIFPA)-INFN, Via Sommarive 14, 38123 Povo (TN), Italy
⁶GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt, Germany

^*Contact author: jorge@itp.uni-frankfurt.de

Phys. Rev. D 113, 055052 – Published 30 March, 2026

DOI: https://doi.org/10.1103/dmzt-4wsz

Abstract

We investigate a dark sector coupled to the Standard Model through a kinetically mixed dark photon $U$ associated with a new $U (1)^{'}$ gauge symmetry. Kinetic mixing, parametrized by $ϵ$ , induces an effective coupling to the electromagnetic current, while the dark photon interacts with a stable dark matter (DM) particle $χ$ through a dark gauge coupling $g_{χ}$ , defining a four-dimensional parameter space $(m_{U}, ϵ, m_{χ}, g_{χ})$ . Our analysis is based on the parton-hadron-string dynamics (PHSD) transport approach, extended to include dark photon production and decay into dileptons ( $U \to e^{+} e^{-}$ ). In PHSD, dark photons are produced in high-energy collisions through Dalitz decays of light mesons ( $π^{0}, η, η^{'}, ω$ ), delta resonances ( $Δ \to N U$ ), direct vector meson decays ( $ρ, ω, ϕ \to U$ ), kaon decays ( $K^{+} \to π^{+} U$ ), and $q \bar{q} \to U$ annihilation. Building on previous PHSD benchmarks against dilepton data, we extract upper limits on $ϵ^{2} (m_{U}, m_{χ}, α_{χ})$ in both the visible regime ( $m_{U} < 2 m_{χ}$ ), where $U \to e^{+} e^{-}$ dominates, and the invisible regime ( $m_{U} > 2 m_{χ}$ ), where $U \to χ \bar{χ}$ is kinematically open and suppresses the dilepton branching fraction. Cosmological and astrophysical constraints are incorporated in two complementary ways. First, we compute the velocity-dependent self-interaction cross section $σ / m_{χ}$ for Yukawa-Mediated self-interacting dark matter and confront it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, we determine thermal relic target curves by computing the relic abundance and requiring $Ω_{DM} h^{2} ≃ 0.12$ , consistent with Planck measurements of the cosmic microwave background. Combining PHSD limits on $ϵ^{2}$ with relic density and self-interaction requirements, we exclude regions of the $(m_{χ}, m_{U})$ plane for each DM realization (Dirac fermion, Majorana fermion, or complex scalar) and identify benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.

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Phys. Rev. D 113, 055052– Published 30 March, 2026

Vol. 113, Iss. 5 — 1 March 2026

Received 28 January 2026
Accepted 13 March 2026

DOI: https://doi.org/10.1103/dmzt-4wsz

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Combined constraints on dark photons from high-energy collisions, cosmology, and astrophysics

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