New Primordial-Magnetic-Field Limit from The Latest LIGO S5 data

TL;DR

This paper uses LIGO S5 gravitational wave data to set new upper limits on primordial magnetic field strengths at different scales, linking gravitational wave observations to early universe magnetic phenomena.

Contribution

It derives the first constraints on primordial magnetic fields based on the latest LIGO S5 gravitational wave upper limits, connecting GW data with early universe magnetic field models.

Findings

For a 1 Mpc scale, PMF amplitude must be less than 4×10⁻⁷ Gauss.

For a 100 Mpc scale, PMF amplitude must be less than 9×10⁻¹¹ Gauss.

GW observations can constrain primordial magnetic fields.

Abstract

Since the energy momentum tensor of a magnetic field always contains a spin-2 component in its anisotropic stress, stochastic primordial magnetic field (PMF) in the early universe must generate stochastic gravitational wave (GW) background. This process will greatly affect the relic gravitational wave (RGW), which is one of major scientific goals of the laser interferometer GW detections. Recently, the fifth science (S5) run of laser interferometer gravitational-wave observatory (LIGO) gave a latest upper limit $\Omega_{GW}<6.9\times10^{-6}$ on the RGW background. Utilizing this upper limit, we derive new PMF Limits: for a scale of galactic cluster $\lambda=1$ Mpc, the amplitude of PMF, that produced by the electroweak phase transition (EPT), has to be weaker than $B_{\lambda} \leq 4\times 10^{-7}$ Gauss; for a scale of supercluster $\lambda=100$ Mpc, the amplitude of PMF has to be weaker than $B_{\lambda} \leq 9\times 10^{-11}$ Gauss. In this manner, GW observation has potential to make interesting contributions to the study of primordial magnetic field.