paper

Planck 2015 results. XIX. Constraints on primordial magnetic fields

arXiv:1502.01594 · doi:10.1051/0004-6361/201525821

Abstract

We compute and investigate four types of imprint of a stochastic background of primordial magnetic fields (PMFs) on the cosmic microwave background (CMB) anisotropies: the impact of PMFs on the CMB spectra; the effect on CMB polarization induced by Faraday rotation; the impact of PMFs on the ionization history; magnetically-induced non-Gaussianities; and the magnetically-induced breaking of statistical isotropy. Overall, Planck data constrain the amplitude of PMFs to less than a few nanogauss. In particular, individual limits coming from the analysis of the CMB angular power spectra, using the Planck likelihood, are nG (where is the comoving field amplitude at a scale of 1 Mpc) at 95% confidence level, assuming zero helicity, and nG for a maximally helical field.For nearly scale-invariant PMFs we obtain nG and nG if the impact of PMFs on the ionization history of the Universe is included. From the analysis of magnetically-induced non-Gaussianity we obtain three different values, corresponding to three applied methods, all below 5 nG. The constraint from the magnetically-induced passive-tensor bispectrum is nG. A search for preferred directions in the magnetically-induced passive bispectrum yields nG, whereas the the compensated-scalar bispectrum gives nG. The analysis of the Faraday rotation of CMB polarization by PMFs uses the Planck power spectra in and at 70 GHz and gives nG. In our final analysis, we consider the harmonic-space correlations produced by Alfvén waves, finding no significant evidence for the presence of these waves. Together, these results comprise a comprehensive set of constraints on possible PMFs with Planck data.

29 pages, 15 figures. Revised following referee report

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