Prospects for determination of thermal history after inflation with future gravitational wave detectors

TL;DR

Future space-based gravitational wave detectors like DECIGO and BBO could precisely determine the Universe's thermal history after inflation, including reheating temperature and equation of state, by analyzing primordial gravitational waves.

Contribution

This paper demonstrates the potential of future gravitational wave detectors to simultaneously measure the reheating temperature and equation of state after inflation using Fisher information analysis.

Findings

Reheating temperature around 10^7 GeV can be accurately determined for tensor-to-scalar ratio ~0.1.

The equation of state of the early Universe can be distinguished if gravitational waves are detected.

Future detectors can reveal the thermal history of the Universe at energies around 10^7 GeV.

Abstract

Thermal history of the Universe between inflation and big-bang nucleosynthesis has not yet been revealed observationally. It will be probed by the detection of primordial gravitational waves generated during inflation, which contain information on the reheating temperature as well as the equation of state of the Universe after inflation. Based on Fisher information formalism, we examine how accurately the tensor-to-scalar ratio and reheating temperature after inflation can be simultaneously determined with space-based gravitational wave detectors such as the DECI-hertz Interferometer Gravitational-wave Observatory (DECIGO) and the Big-Bang Observer (BBO). We show that the reheating temperature is best determined if it is around 10^7 GeV for tensor-to-scalar ratio of around 0.1, and explore the detectable parameter space. We also find that equation of state of the early Universe can be also determined accurately enough to distinguish different equation-of-state parameters if the inflationary gravitational waves are successfully detected. Thus future gravitational wave detectors provide a unique and promising opportunity to reveal the thermal history of the Universe around 10^7 GeV.