  We study a model of dark matter in which the hidden sector interacts with
standard model particles via a hidden photonic portal. We investigate the
effects of this new interaction on the hydrogen atom, including the Stark,
Zeeman and hyperfine effects. Using the accuracy of the measurement of energy,
we obtain an upper bound for the coupling constant of the model. We also
calculate the contribution from the hidden photonic portal to the anomalous
magnetic moment of the muon, which provides an important probe of physics
beyond the standard model.
