Superfluids and the Cosmological Constant Problem
  We introduce a novel method to circumvent Weinberg's no-go theorem for
self-tuning the cosmological vacuum energy: a Lorentz-violating
finite-temperature superfluid can counter the effects of an arbitrarily large
cosmological constant. Fluctuations of the superfluid result in the graviton
acquiring a Lorentz-violating mass and we identify a unique class of theories
that are pathology free, phenomenologically viable, and do not suffer from
instantaneous modes. This new and hitherto unidentified phase of massive
gravity propagates the same degrees of freedom as general relativity with an
additional Lorentz-violating scalar that is introduced by higher-derivative
operators in a UV insensitive manner. The superfluid is therefore a consistent
infrared modification of gravity. We demonstrate how the superfluid can
degravitate a cosmological constant and discuss its phenomenology.
