  The nature of dark matter (DM) is still a mystery that may indicate the
necessity for extensions of the Standard Model (SM). Light dark photons (DP)
may comprise partially or entirely the observed DM density and existing limits
on the DP DM parameter space arise from several cosmological and astrophysical
sources. In the present work we investigate DP DM using cosmic transients,
specifically fast radio bursts (FRBs). The observed time delay of radio photons
with different energies have been used to constrain the photon mass or the Weak
Equivalence Principle, for example. Due to the mixing between the visible and
the DP, the time delay of photons from these cosmic transients, caused by free
electrons in the intergalactic medium, can change and impact those constraints
from FRBs. We use five detected FRBs and two associations of FRBs with
gamma-ray bursts to investigate the correspondent variation on the time delay
caused by the presence of DP DM. The result is virtually independent of the FRB
used and this variation is very small, considering the still allowed DP DM
parameter space, not jeopardizing current bounds on other contributions of the
observed time delay.
