Abstract
A self-consistent and gauge-invariant model of light dark matter coupled to the Standard Model through concurrent vector and scalar portals is developed. The framework extends the gauge group by an additional \(\textrm{U}(1)_{V}\) symmetry featuring a kinetically mixed vector boson and a complex scalar singlet interacting with the Higgs doublet via mixing. Effective interaction Lagrangians are derived, and the phenomenology of the small-mixing, light-mediator regime is analyzed. Numerical simulations of associated dark matter production with a \(\tau^{+}\tau^{-}\) pair in \(e^{+}e^{-}\) collisions at \(\sqrt{s}=7~\textrm{GeV}\) are performed, with signal and background cross sections evaluated to obtain sensitivity contours in the \([m_{\chi},y]\) parameter plane. Even for \(\sin\theta\sim 10^{-4}\) , the scalar portal provides a nonnegligible contribution, emphasizing the phenomenological relevance of the combined portal framework compared with single-vector–mediator scenarios.
