Journal
PHYSICAL REVIEW D
Volume 105, Issue 12, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.105.123502
Keywords
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Funding
- French National Research Agency (ANR) [ANR-19-CE31-0020]
- Shota Rustaveli National Science Foundation (SRNSF) of Georgia [FR/18-1462, A0090412058]
- Grand Equipement National de Calcul Intensif (GENCI)
- Agence Nationale de la Recherche (ANR) [ANR-19-CE31-0020] Funding Source: Agence Nationale de la Recherche (ANR)
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The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA) Collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (SGWB) in the 1-100 nHz frequency range. They performed magnetohydrodynamic (MHD) simulations to study the dynamical evolution of the magnetic field and compute the resulting SGWB. By comparing the SGWB signal with the PTA data, they constrained the temperature scale, amplitude, and characteristic scale of the initial magnetic field, and showed that the turbulent decay of this magnetic field can alleviate the Hubble tension.
The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA) Collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (SGWB) in the 1-100 nHz frequency range. We consider the scenario in which this signal is produced by magnetohydrodynamic (MHD) turbulence in the early Universe, induced by a nonhelical primordial magnetic field at the energy scale corresponding to the quark confinement phase transition. We perform MHD simulations to study the dynamical evolution of the magnetic field and compute the resulting SGWB. We show that the SGWB output from the simulations can be very well approximated by assuming that the magnetic anisotropic stress is constant in time, over a time interval related to the eddy turnover time. The analytical spectrum that we derive under this assumption features a change of slope at a frequency corresponding to the GW source duration that we confirm with the numerical simulations. We compare the SGWB signal with the PTA data to constrain the temperature scale at which the SGWB is sourced, as well as the amplitude and characteristic scale of the initial magnetic field. We find that the generation temperature is constrained to be in the 1-200 MeV range, the magnetic field amplitude must be >1% of the radiation energy density at that time, and the magnetic field characteristic scale is constrained to be >10% of the horizon scale. We show that the turbulent decay of this magnetic field will lead to a field at recombination that can help to alleviate the Hubble tension and can be tested by measurements in the voids of the Large Scale Structure with gamma-ray telescopes like the Cherenkov Telescope Array.
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