New stellar constraints on dark photons

TL;DR

This work revisits stellar production of dark photons in the minimal kinetic-mixing model and shows that, for $m_V<\omega_p$, the emission is dominated by the longitudinal mode with a scaling $Rate_{SM\to V_L} \propto \kappa^2 m_V^2$, correcting earlier claims of $m_V^4$ decoupling. The authors develop a proper in-medium treatment via the polarization tensor, derive resonant production rates, and apply solar and horizontal-branch constraints to sharpen the viable $(\kappa,m_V)$ parameter space, finding significantly stronger bounds for $m_V<\mathcal{O}(1-10)$ eV. Consequently, current light-shining-through-wall experiments lie within regions excluded by stellar bounds, altering the landscape for laboratory searches of dark photons. This work also clarifies methodological issues in previous analyses and highlights the importance of longitudinal-mode dynamics in low-mass, weakly coupled sectors.

Abstract

We consider the stellar production of vector states V within the minimal model of "dark photons". We show that when the Stuckelberg mass of the dark vector becomes smaller than plasma frequency, the emission rate is dominated by the production of the longitudinal modes of V, and scales as κ^2 m_V^2, where κand m_V are the mixing angle with the photon and the mass of the dark state. This is in contrast with earlier erroneous claims in the literature that the emission rate decouples as the forth power of the mass. We derive ensuing constraints on the (κ, m_V) parameter space by calculating the cooling rates for the Sun and red giant stars. We find that stellar bounds for m_V < 10 eV are significantly strengthened, to the extent that all current "light-shining-through-wall" experiments find themselves within deeply excluded regions.

Figures (2)

• Figure 1: Illustration of the dark photon emission process by the electromagnetic current.
• Figure 2: Upper limits on the kinetic mixing parameter $\kappa$ vs. the mass of the dark photon $m_V$. The solid blue and red curves are the total constraints on the dark photon parameter space from the sun (blue) and horizontal branch stars (red). The dashed curves show constraints from retaining only the longitudinal resonance contributions. For comparison, the dot-dashed curve shows the upper limit by considering only the contribution from transverse modes and the dotted curve shows the constraint from the CAST experiment by only considering the contribution from the transverse mode Redondo:2008aa. The current bounds from the latest result of the LSW experiment by the ALPS collaboration Ehret:2010mh is shown in gray, accompanied by the potential reach (yellow region) of the next generation of LSW experiments Redondo:2010dp.