Pseudo-Goldstone dark matter: gravitational waves and direct-detection
  blind spots
  Pseudo-Goldstone dark matter is a thermal relic with momentum-suppressed
direct-detection cross section. We study the most general model of
pseudo-Goldstone dark matter arising from the complex-singlet extension of the
Standard Model. The new U(1) symmetry of the model is explicitly broken down to
a CP-like symmetry stabilising dark matter. We study the interplay of
direct-detection constraints with the strength of cosmic phase transitions and
possible gravitational-wave signals. While large U(1)-breaking interactions can
generate a large direct-detection cross section, there are blind spots where
the cross section is suppressed. We find that sizeable cubic couplings can give
rise to a first-order phase transition in the early universe. We show that
there exist regions of the parameter space where the resulting
gravitational-wave signal can be detected in future by the proposed Big Bang
Observer detector.
