Binary pulsars as probes of a Galactic dark matter disk
  As a binary pulsar moves through a wind of dark matter particles, the
resulting dynamical friction modifies the binary's orbit. We study this effect
for the double disk dark matter (DDDM) scenario, where a fraction of the dark
matter is dissipative and settles into a thin disk. For binaries within the
dark disk, this effect is enhanced due to the higher dark matter density and
lower velocity dispersion of the dark disk, and due to its co-rotation with the
baryonic disk.We estimate the effect and compare it with observations for two
different limits in the Knudsen number ($Kn$). First, in the case where DDDM is
effectively collisionless within the characteristic scale of the binary
($Kn\gg1$) and ignoring the possible interaction between the pair of dark
matter wakes. Second, in the fully collisional case ($Kn\ll1$), where a fluid
description can be adopted and the interaction of the pair of wakes is taken
into account. We find that the change in the orbital period is of the same
order of magnitude in both limits. A comparison with observations reveals good
prospects to probe currently allowed DDDM models with timing data from binary
pulsars in the near future. We finally comment on the possibility of extending
the analysis to the intermediate (rarefied gas) case with $Kn\sim1$.
