Anomalous $U(1)$ Gauge Bosons as Light Dark Matter in String Theory
  Present experiments are sensitive to very weakly coupled extra gauge
symmetries which motivates further investigation of their appearance in string
theory compactifications and subsequent properties. We consider extensions of
the standard model based on open strings ending on D-branes, with gauge bosons
due to strings attached to stacks of D-branes and chiral matter due to strings
stretching between intersecting D-branes. Assuming that the fundamental string
mass scale saturates the current LHC limit and that the theory is weakly
coupled, we show that (anomalous) $U(1)$ gauge bosons which propagate into the
bulk are compelling light dark matter candidates. We comment on the possible
relevance of the $U(1)$ gauge bosons, which are universal in intersecting
D-brane models, to the observed $3\sigma$ excess in XENON1T.
