Phsd Analysis Constrains Dark Photons, Achieving Limits on Ε at 1

Scientists are increasingly focused on understanding dark matter, and a new study led by A. W. Romero Jorge (Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University, and GSI Helmholtz Center for Heavy Ion Physics), L. Sagunski, and Guan-Wen Yuan (University of Trento and TIFPA-INFN) et al, presents compelling combined constraints on ‘dark photons’ , hypothetical particles mediating interactions within the dark sector. Their research, utilising the parton-hadron-string dynamics (PHSD) transport approach alongside cosmological and astrophysical data, significantly refines the search for these elusive particles by examining production and decay in high-energy collisions, as well as self-interaction and relic abundance requirements. This multi-pronged approach allows the team to exclude previously viable regions of parameter space and pinpoint benchmark scenarios where heavy-ion, cosmological, and astrophysical observations align, offering a crucial step towards unveiling the nature of dark matter.

Dark photon limits from heavy-ion collisions are becoming

Scientists have demonstrated a novel approach to constrain dark photon models by combining heavy-ion collision data with cosmological and astrophysical observations. The team achieved this by extending the parton, hadron, string dynamics (PHSD) transport approach to include the production and decay of dark photons into dileptons (U → e+e−). This innovative method allows for the extraction of upper limits on the kinetic mixing parameter, ε2(mU, mχ, αχ), in both visible (mU 2mχ) regimes, where the dark photon decays are dominated by different channels. Experiments show that dark photons are produced in high-energy collisions through various processes, including Dalitz decays of light mesons (π0, η, η′, ω), Delta-resonances (∆→NU), direct vector meson decays (ρ, ω, φ →U), kaon decays (K+ →π+U), and quark-quark annihilation.
The study reveals that cosmological and astrophysical constraints are incorporated in two complementary ways, enhancing the robustness of the analysis. First, researchers computed the velocity-dependent self-interaction cross section σ/mχ for Yukawa-mediated self-interacting dark matter (SIDM) and compared it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, they determined thermal relic target curves by calculating the relic abundance and requiring ΩDMh2 ≃ 0.12, consistent with Planck measurements of the cosmic microwave background. This comprehensive approach allows for the exclusion of regions of the (mχ, mU) plane for different dark matter realizations, Dirac fermions, Majorana fermions, or complex scalars, and identifies benchmark scenarios where heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.

This breakthrough establishes a strong connection between particle physics, cosmology, and astrophysics, offering a multi-faceted approach to probing the dark sector. The research establishes upper limits on ε2 in both the visible and invisible regimes, providing crucial constraints on dark photon models. By combining PHSD limits on ε2 with relic density and self-interaction requirements, the team successfully excluded regions of the parameter space and pinpointed viable scenarios for dark matter. The work opens new avenues for exploring light mediators and non-minimal dark sectors, potentially leading to a conclusive detection of dark matter in the future.

Furthermore, the study unveils the potential of heavy-ion collisions as a complementary tool to traditional direct and indirect detection methods. By leveraging the unique environment created in these collisions, scientists can access previously unexplored regions of parameter space and gain valuable insights into the properties of dark matter. The combined constraints from high-energy collisions, cosmology, and astrophysics provide a powerful framework for unraveling the mysteries of the dark universe and understanding its fundamental constituents. This research is a significant step towards building a complete picture of the cosmos and the elusive dark matter that permeates it.

PHSD Modelling of Dark Photon Dilepton Production

Scientists employed the Parton-Hadron-String Dynamics (PHSD) transport approach, extending it to model dark photon (U) production and subsequent decay into dileptons (e+e−). This work meticulously details how dark photons, coupled to the Standard Model through kinetic mixing, were incorporated into the PHSD framework to investigate their potential contribution to the dilepton spectrum. The team engineered a system where dark photons are generated in high-energy collisions via several channels, including Dalitz decays of light mesons (π0, η, η′), Delta-resonance decays (∆), direct vector meson decays (ρ, ω, φ), kaon decays, and quark-quark annihilation. Experiments meticulously tracked dark photon production through these channels, calculating rates based on established partial-width ratios and branching fractions from prior research.

For instance, rates for Dalitz-type decays were derived from corresponding virtual-photon decays, directly yielding branching ratios for meson-to-dark photon transitions. The ∆→NU contribution was evaluated using the ∆ spectral function and a mass-dependent total width, ensuring accurate modelling of this decay process. Direct decays of vector mesons were implemented by substituting virtual photons with dark photons, scaled by an effective coupling α′ = α ε2, where ε represents the kinetic mixing parameter. The study pioneered a method for incorporating partonic channels, rescaling the PHSD quark-quark to dilepton yield with ε2, leveraging the off-shell nature of Dynamical Quasi-Particle Model (DQPM) partons to allow single-U production.

This innovative approach enables the calculation of the total dilepton yield from both hadronic and partonic sources, accounting for the visible branching fraction of dark photon decays into electron-positron pairs. The team harnessed this capability to extract upper limits on ε2 in both the visible (Mee ≲ 3 GeV/c2) and invisible regimes (Mee 3 GeV/c2), where kinematic constraints differ. To quantify the maximal dark photon contribution consistent with the PHSD Standard Model (SM) dilepton yield, researchers introduced a surplus factor (CU) in each invariant-mass bin of 10 MeV width. They required that the dark photon dilepton yield in each bin be less than or equal to CU times the SM yield, effectively capturing experimental precision and setting limits on the kinetic mixing parameter ε2 for a given dark photon mass (mU). This precise measurement approach, combined with cosmological and astrophysical constraints, allows the exclusion of regions in the ε2-mU parameter space and identification of benchmark scenarios satisfying multiple observational criteria.

Dark photon limits from high-energy collisions are becoming

Scientists have achieved groundbreaking results in the search for dark matter, revealing stringent upper limits on dark photon interactions and providing insights into the nature of self-interacting dark matter. The research, based on the parton-hadron-string dynamics (PHSD) transport approach, investigates a dark sector coupled to the Standard Model through a kinetically mixed dark photon. Experiments revealed that dark photons are produced in high-energy collisions via Dalitz decays of light mesons, Delta-resonances, direct vector meson decays, kaon decays, and annihilation processes within the PHSD framework. The team measured upper limits on the kinetic mixing parameter, ε, in both the visible regime (mU Data shows that in the visible regime, where decays to Standard Model particles dominate, the limits are particularly sensitive to dilepton production.

Tests prove that the invisible regime, where decays into stable dark matter are kinematically accessible, allows for probing a wider range of dark sector parameters. Specifically, the study extracts upper limits on ε, crucial for constraining models of dark matter interactions. Results demonstrate that the velocity-dependent self-interaction cross section for Yukawa-mediated self-interacting dark matter (SIDM) was confronted with bounds from dwarf galaxies, galaxy groups, and clusters. Measurements confirm that the research incorporates cosmological and astrophysical constraints in two complementary ways, utilising thermal relic target curves derived from the relic abundance and requiring a relic density consistent with Planck measurements of the cosmic microwave background.

The breakthrough delivers exclusion regions in the (mχ, mU) plane for each dark matter realization, Dirac, Majorana, or complex scalar, by combining PHSD limits on ε with relic density and self-interaction requirements. Scientists recorded benchmark scenarios where heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied, offering promising avenues for future experimental tests. The study meticulously calculates decay rates, finding that for Dirac fermions, the invisible decay rate scales with Γ(U → χχ) ∝ αχ mU (1 + 2m2 χ / m2 U) s (1 − 4m2 χ / m2 U), while for Majorana fermions and complex scalars, the rate is suppressed due to the axial-vector current and phase space factors. Figures illustrate the dileptonic branching fraction, Br(U → e+e−), in the (mU, mχ) plane, showcasing a pronounced transition at mU = 2mχ where the invisible decay channel dominates, reducing the visible branching fraction to below 10−2 in certain regions.

Dark photon limits from high-energy collisions are becoming

Scientists have investigated a dark sector interacting with the Standard Model via a kinetically mixed dark photon, alongside stable dark matter particles. Their analysis, utilising the parton-hadron-string dynamics (PHSD) transport approach, examined the production and decay of these dark photons into dileptons within high-energy collisions. The PHSD model was extended to account for dark photon creation through various processes, including Dalitz decays of mesons, Delta-resonance decays, direct vector meson decays, kaon decays, and annihilation, allowing for detailed modelling of particle interactions. Researchers extracted upper limits on the kinetic mixing parameter across both visible and invisible regimes, incorporating cosmological and astrophysical constraints to refine their findings.

They assessed velocity-dependent self-interaction cross sections for Yukawa-mediated self-interacting dark matter, comparing these to observations of dwarf galaxies, galaxy groups, and clusters, ensuring consistency with established astrophysical data. Furthermore, they determined thermal relic target curves based on relic abundance calculations, aligning with measurements from the Planck cosmic microwave background mission. By combining PHSD limits with relic density and self-interaction requirements, the team excluded regions of parameter space and identified benchmark scenarios satisfying multiple constraints simultaneously. The authors acknowledge that their bounds on kinetic mixing do not, in themselves, guarantee a viable dark matter scenario, as the same mediator governing dark photon phenomenology also influences dark matter self-scattering within astrophysical halos. Future research should focus on refining the PHSD model and exploring a wider range of dark sector parameters to further constrain the properties of dark matter and its interactions, potentially resolving tensions between simulations and observations of galactic structures. This work represents a significant step towards understanding the nature of dark matter and its role in the universe.