---
author:
- 'Daniel G. Figueroa'
- 'and Erwin H. Tanin'
bibliography:
- 'referencesSTIFF.bib'
title: Ability of LIGO and LISA to probe the equation of state of the early Universe
---

Introduction
============

Observations of the cosmic microwave background (CMB) and the large scale structures of the Universe strongly support the idea that the Universe underwent a period of cosmic inflation at its early stages. Apart from solving the horizon and flatness problems, and providing the appropriate initial conditions for primordial density perturbations, inflation is a very natural phenomenon. The most recent measurement of the B-mode polarization anisotropies of the CMB [@Akrami:2018odb; @Ade:2018gkx] sets a bound on the inflationary Hubble rate which corresponds to an energy scale $\lesssim 10^{16}\text{ GeV}$. At some point below this energy scale, the energy budget of the universe must be converted into a thermal bath of radiation in order to switch to the standard hot Big Bang cosmology, from which point the expansion history is well known. To explain the observed abundance of light elements in the universe, Big Bang Nucleosynthesis (BBN) must take place during the radiation domination (RD) epoch, starting at a temperature of around $T_{\rm BBN}\sim 1 \text{ MeV}$, when the energy 