Dark matter superfluid and DBI dark energy
  It was shown recently that, without jeopardizing the success of the $\Lambda$
cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND)
can be derived as an emergent phenomenon when axionlike dark matter particles
condense into superfluid on the galactic scales. We propose in this paper a
Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter
components. To maintain the success of MOND phenomenon of dark matter
superfluid on the galactic scales, the fifth force introduced by the DBI scalar
should be screened on the galactic scales. It turns out that the screening
effect naturally leads to a simple explanation for a longstanding puzzle that
the MOND critical acceleration coincides with present Hubble scale. This
galactic coincidence problem is solved, provided that the screened DBI scalar
also plays the role of dark energy on the cosmic scales.
