New Sensitivity Curves for Gravitational-Wave Signals from Cosmological
  Phase Transitions
  Gravitational waves (GWs) from strong first-order phase transitions (SFOPTs)
in the early Universe are a prime target for upcoming GW experiments. In this
paper, I construct novel peak-integrated sensitivity curves (PISCs) for these
experiments, which faithfully represent their projected sensitivities to the GW
signal from a cosmological SFOPT by explicitly taking into account the expected
shape of the signal. Designed to be a handy tool for phenomenologists and model
builders, PISCs allow for a quick and systematic comparison of theoretical
predictions with experimental sensitivities, as I illustrate by a large range
of examples. PISCs also offer several advantages over the conventional
power-law-integrated sensitivity curves (PLISCs); in particular, they directly
encode information on the expected signal-to-noise ratio for the GW signal from
a SFOPT. I provide semianalytical fit functions for the exact numerical PISCs
of LISA, DECIGO, and BBO. In an appendix, I moreover present a detailed review
of the strain noise power spectra of a large number of GW experiments. The
numerical results for all PISCs, PLISCs, and strain noise power spectra
presented in this paper can be downloaded from the Zenodo online repository
[https://doi.org/10.5281/zenodo.3689582]. In a companion paper [1909.11356],
the concept of PISCs is used to perform an in-depth study of the GW signal from
the cosmological phase transition in the real-scalar-singlet extension of the
standard model. The PISCs presented in this paper will need to be updated
whenever new theoretical results on the expected shape of the signal become
available. The PISC approach is therefore suited to be used as a bookkeeping
tool to keep track of the theoretical progress in the field.
