Speaker
Description
We investigate a dark sector coupled to the Standard Model (SM) via a kinetically mixed dark photon $U$ associated with an additional $U(1)'$ gauge symmetry. The kinetic mixing parameter $\varepsilon$ induces an effective coupling to the electromagnetic current, while interactions with a stable dark matter (DM) particle $\chi$ are governed by a dark gauge coupling $g_\chi$, spanning the four-dimensional parameter space $(m_U,\varepsilon,m_\chi,g_\chi)$. Our study employs the parton--hadron--string dynamics (PHSD) transport approach, extended to model dark-photon production and its dilepton decay channel ($U\to e^+e^-$). Within PHSD, dark photons are generated in high-energy collisions through multiple sources, including Dalitz decays of light mesons ($\pi^0,\eta,\eta',\omega$), $\Delta$-resonance transitions ($\Delta\to N U$), direct vector-meson decays ($\rho,\omega,\phi\to U$), kaon decays ($K^+\to\pi^+U$), and quark--antiquark annihilation ($q\bar q\to U$). Using established PHSD validations against dilepton measurements as a baseline, we derive upper bounds on $\varepsilon^2(m_U,m_\chi,\alpha_\chi)$ in both the visible regime ($m_U<2m_\chi$), where $U\to e^+e^-$ is dominant, and the invisible regime ($m_U>2m_\chi$), where the opening of $U\to\chi\bar\chi$ reduces the dilepton branching ratio. Cosmological and astrophysical information is included in two complementary steps. First, we evaluate the velocity-dependent self-interaction cross section $\sigma/m_\chi$ for Yukawa-mediated self-interacting DM (SIDM) and compare it to constraints from dwarf galaxies, galaxy groups, and clusters. Second, we compute thermal freeze-out target curves by solving for the relic abundance and imposing $\Omega_{\rm DM}h^2\simeq 0.12$, consistent with Planck cosmic-microwave-background determinations. By combining the PHSD-driven limits on $\varepsilon^2$ with relic-density and self-interaction requirements, we delineate excluded regions in the $(m_\chi,m_U)$ plane for different DM realizations (Dirac fermion, Majorana fermion, and complex scalar), and we highlight benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints can be satisfied simultaneously.
| Main Contribution topic | Theory / Phenomenology |
|---|---|
| Secondary contribution topic | Astrophysical observations |