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

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 $1\mathrm{Mpc}$ as $B_{1\mathrm{Mpc}}<3.1\mathrm{nG}$ at $95$ C.L.

Comments: 6 pages, 1 figure. Accepted for publication in PRD