Gravitational waves from a holographic phase transition
  We investigate first order phase transitions in a holographic setting of
five-dimensional Einstein gravity coupled to a scalar field, constructing phase
diagrams of the dual field theory at finite temperature. We scan over the
two-dimensional parameter space of a simple bottom-up model and map out
important quantities for the phase transition: the region where first order
phase transitions take place; the latent heat, the transition strength
parameter $\alpha$, and the stiffness. We find that $\alpha$ is generically in
the range 0.1 to 0.3, and is strongly correlated with the stiffness (the square
of the sound speed in a barotropic fluid). Using the LISA Cosmology Working
Group gravitational wave power spectrum model corrected for kinetic energy
suppression at large $\alpha$ and non-conformal stiffness, we outline the
observational prospects at the future space-based detectors LISA and TianQin. A
TeV-scale hidden sector with a phase transition described by the model could be
observable at both detectors.
