  Mirror dark matter provides a simple framework for which to explain the
DAMA/Libra annual modulation signal consistently with the null results of the
other direct detection experiments. The simplest possibility involves ordinary
matter interacting with mirror dark matter via photon-mirror photon kinetic
mixing of strength epsilon ~ 10^(-9). We confirm that photon-mirror photon
mixing of this magnitude is consistent with constraints from ordinary Big Bang
nucleosynthesis as well as the more stringent constraints from cosmic microwave
background measurements and large scale structure considerations.
