NANOGrav signal from MHD turbulence at QCD phase transition in the early universe

TL;DR

The paper proposes that the NANOGrav gravitational wave signal could originate from MHD turbulence during the QCD phase transition, linking early universe magnetic fields to current cosmological tensions and testable magnetic relics.

Contribution

It introduces a novel MHD turbulence model at the QCD scale as the source of the NANOGrav signal, connecting early magnetic fields to observable relics and the Hubble tension.

Findings

Magnetic field parameters inferred from NANOGrav data.

Decay of non-helical magnetic fields can solve the Hubble tension.

Testable predictions for relic magnetic fields in large-scale structures.

Abstract

The NANOGrav collaboration has recently reported evidence for the existence of a stochastic gravitational wave background in the 1-100 nHz frequency range. We argue that such background could have been produced by magneto-hydrodynamic (MHD) turbulence at the QCD scale. From the NANOGrav measurement one can infer the magnetic field parameters: comoving field strength close to microGauss and a correlation length close to 10\% of the Hubble radius at the QCD phase transition epoch. We point out that the turbulent decay of a non-helical magnetic field with such parameters leads to a magnetic field at the recombination epoch, which would be sufficiently strong to provide a solution to the Hubble tension problem, as recently proposed. We also show that the MHD turbulence interpretation of the NANOGrav signal can be tested via measurements of the relic magnetic field in the voids of the large scale structure, with gamma-ray telescopes like CTA.