Running in the Dark Sector

Hooman Davoudiasl, William J. Marciano

Published 2015-02-25Version 1

The "dark photon" $\gamma_d$ of a gauged $U(1)_d$ can become effectively invisible if it primarily decays into light states from a dark sector. We point out that, in such scenarios, the running of the $U(1)_d$ "fine structure constant" $\alpha_d$ can be significant - over the kinematic range of typical experiments - and provide a probe of the spectrum of dark particles. For $\alpha_d > {\rm few}\times 0.1$, the running can substantially modify some existing predictions for "beam dump" experiments. These features are demonstrated in simple models that contain light dark matter and a scalar that breaks $U(1)_d$. We also discuss theoretic considerations, regarding the $U(1)_d$ model in the ultraviolet regime, that can potentially imply the infrared upper bound $\alpha_d < 0.1$.