Are symmetric tidal streams possible with long-range dark-matter forces?
  The unique dynamics of the tidal disruption of satellite galaxies is an
extremely sensitive probe of long-range interactions between dark-matter
particles. Dark-matter forces that are several percent the strength of gravity
will lead to order unity changes in the ratio of the number of stars in the
leading and trailing tidal streams of a satellite galaxy. The approximate
symmetry of the stellar tidal streams of the Sagittarius dwarf galaxy would
thus exclude attractive dark-matter forces greater than 10% the strength of
gravity which would entirely eliminate the leading stream. However, recent
simulations suggest that dark-matter forces 100% the strength of gravity could
completely strip the stellar component of Sagittarius of its dark matter,
allowing for the subsequent development of symmetric tidal streams. Here we
argue that these simulations use inconsistent initial conditions corresponding
to separate pure stellar and pure dark-matter satellites moving independently
in the host galaxy's halo, rather than a single disrupting composite satellite
as had been intended. A new simulation with different initial conditions, in
particular a much more massive satellite galaxy, might demonstrate a scenario
in which symmetric tidal streams develop in the presence of large dark-matter
forces. This scenario must satisfy several highly restrictive criteria
described in this paper.
