Finding sound shells in LISA mock data using likelihood sampling

Abstract

We study to what extent LISA can observe features of gravitational wave spectra originating from cosmological first-order phase transitions. We focus on spectra which are of the form of double-broken power laws. These spectra are predicted by hydrodynamic simulations and also analytical models such as the sound shell model. We argue that the ratio of the two break frequencies is an interesting observable since it can be related to the wall velocity while overall amplitude and frequency range are often degenerate for the numerous characteristics of the phase transition. Our analysis uses mock data obtained from the power spectra predicted by the simplified simulations and the sound shell model and analyzes the detection prospects using χ 2 -minimization and likelihood sampling. We point out that the prospects of observing two break frequencies from the electroweak phase transition is hindered by a shift of the spectrum to smaller frequencies for strong phase transitions. Finally, we also highlight some differences between signals from the sound shell model compared to simulations.

Sound velocity effects on the phase transition gravitational wave spectrum in the sound shell model

“…Thus the calculation of GW power spectra from sound wave is converted to the study of velocity power spectra. In this section, we will briefly introduce the basic set-up of the SSM [13,14,[16][17][18][19] with the schematic process shown in Fig. 1.…”

Prospects for LISA to detect a gravitational-wave background from first order phase transitions

“…Another study looked at LISA's ability to detect to a general double broken power law that has the low and high frequency spectral slopes unspecified [35], instead of fixed at the SSM values. The Akaike Information Criterion was used to determine whether, in the presence of LISA instrument noise, one is able to identify the break frequencies.…”

“…We consider a value of ∆DIC > 5 to be a detection as discussed in more detail in section 2.7. In comparison to [34,35] we use the AET time delay interferometery (TDI) channels to build our data model and use the T channel to constrain the LISA instrument noise in our MCMC simulations. We then perform a systematic scan over the spectral parameter space using Fisher matrix and MCMC methods to determine how well the four spectral parameters of the first order phase transition can be estimated with LISA.…”

Droplet collapse during strongly supercooled transitions

“…Holographic techniques have been used to compute phase transition parameters and gravitational wave signals [12,16,[32][33][34][35]. Preliminary studies have explored the ability of LISA to reconstruct phase transition parameters [36,37]. New simulation techniques [38], valid for weak and intermediate thermal transitions, have enabled the exploration of the effects of density perturbations on the gravitational wave spectrum [39].…”