Axion

Physics

Dark matter

Mathematics

Parameter space

Particle physics

Pulsar

Operating system

Statistics

Astronomy

Physics beyond the Standard Model

Nuclear physics

Gravitational wave

Cosmology

Approx

Computer science

Astrophysics

Spectral line

Universe

SciPost Physics

The NANOGrav collaboration has recently observed first evidence of a gravitational wave background (GWB) in pulsar timing data. Here we explore the possibility that this GWB is due to new physics, and show that the signal can be well fit also with peaked spectra like the ones expected from phase transitions (PTs) or from the dynamics of axion like particles (ALPs) in the early universe. We find that a good fit to the data is obtained for a very strong PT at temperatures around 1 MeV to 10 MeV. For the ALP explanation the best fit is obtained for a decay constant of $F \approx 5\times 10^{17}$ GeV and an axion mass of $2\times 10^{-13}$ eV. We also illustrate the ability of PTAs to constrain the parameter space of these models, and obtain limits which are already comparable to other cosmological bounds.

Whispers from the dark side: Confronting light new physics with NANOGrav data