A fresh look at the gravitationalwave signal from cosmological phase transitions
Abstract
Many models of physics beyond the Standard Model predict a strong firstorder phase transition (SFOPT) in the early Universe that leads to observable gravitational waves (GWs). In this paper, we propose a novel method for presenting and comparing the GW signals that are predicted by different models. Our approach is based on the observation that the GW signal has an approximately modelindependent spectral shape. This allows us to represent it solely in terms of a finite number of observables, that is, a set of peak amplitudes and peak frequencies. As an example, we consider the GW signal in the realscalarsinglet extension of the Standard Model (xSM). We construct the signal region of the xSM in the space of observables and show how it will be probed by future spaceborne interferometers. Our analysis results in sensitivity plots that are reminiscent of similar plots that are typically shown for darkmatter directdetection experiments, but which are novel in the context of GWs from a SFOPT. These plots set the stage for a systematic model comparison, the exploration of underlying modelparameter dependencies, and the construction of distribution functions in the space of observables. In our plots, the experimental sensitivities of future searches for a stochastic GW signal are indicated by peakintegrated sensitivity curves. A detailed discussion of these curves, including fit functions, is contained in a companion paper [1].
 Publication:

Journal of High Energy Physics
 Pub Date:
 March 2020
 DOI:
 10.1007/JHEP03(2020)004
 arXiv:
 arXiv:1909.11356
 Bibcode:
 2020JHEP...03..004A
 Keywords:

 Cosmology of Theories beyond the SM;
 Beyond Standard Model;
 Thermal Field Theory;
 High Energy Physics  Phenomenology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Experiment
 EPrint:
 19+1+5 pages main text / appendix / references, 4 figures. Companion paper: 2002.04615. Data and code available on Zenodo: https://doi.org/10.5281/zenodo.3699415. v2: New section added, comparing our method with existing approaches in the literature. The content of v2 matches the version published in JHEP