First observational constraints on tensor non-Gaussianity sourced by primordial magnetic fields from cosmic microwave background

TL;DR

This paper derives the first observational constraint on tensor non-Gaussianity caused by primordial magnetic fields using WMAP data, setting an upper limit on magnetic field strength.

Contribution

It provides the first observational bounds on tensor non-Gaussianity sourced by primordial magnetic fields from CMB temperature maps.

Findings

Tensor non-Gaussianity is consistent with zero.

Upper bound on PMF strength is 3.1 nG at 95% C.L.

Constraints improve understanding of primordial magnetic fields.

Abstract

Primordial magnetic fields (PMFs) create a large squeezed-type non-Gaussianity in tensor perturbation, which generates non-Gaussian temperature fluctuations in the cosmic microwave background (CMB). We for the first time derive an observational constraint on such a tensor non-Gaussianity from observed CMB maps. Analyzing temperature maps of the WMAP 7-year data, we find that such a tensor non-Gaussianity is consistent with zero. This gives an upper bound on PMF strength smoothed on $1 ~ {\rm Mpc}$ as $B_{1 ~ \rm Mpc} < 3.1 ~{\rm nG}$ at $95%$ C.L.