  Dark matter charged under a new gauge sector, as motivated by recent data,
suggests a rich GeV-scale "dark sector" weakly coupled to the Standard Model by
gauge kinetic mixing. The new gauge bosons can decay to Standard Model leptons,
but this mode is suppressed if decays into lighter dark sector particles are
kinematically allowed. These particles in turn typically have macroscopic decay
lifetimes that are constrained by two classes of experiments, which we discuss.
Lifetimes of 10 cm < c tau < 10^8 cm are constrained by existing terrestrial
beam-dump experiments. If, in addition, dark matter captured in the Sun (or
Earth) annihilates into these particles, lifetimes up to 10^15 cm are
constrained by solar observations. These bounds span fourteen orders of
magnitude in lifetime, but they are not exhaustive. Accordingly, we identify
promising new directions for experiments including searches for displaced
di-muons in B-factories, studies at high-energy and -intensity proton beam
dumps, precision gamma-ray and electronic measurements of the Sun, and
milli-charge searches re-analyzed in this new context.
