CMB Non-Gaussianity as a Probe of Primordial Magnetic Fields

Pranjal Trivedi

August 20, 2012

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Abstract: Magnetic fields are observed in galaxies and clusters of galaxies and are possibly present throughout the Universe. However, the origin of cosmic magnetic fields is a puzzle. An interesting possibility is that large-scale magnetic fields are of primordial origin, formed in the early Universe. Such magnetic fields will alter the fluctuations of the cosmic microwave background (CMB). In particular, intrinsically non-linear magnetic effects introduce a new kind of non-Gaussianity in the CMB fluctuations. I will describe recent work on calculations of the magnetic CMB trispectrum and bispectrum. These non-Gaussian correlations constrain magnetic fields better than the CMB power spectrum. Further, the trispectrum is found to be a more sensitive probe of magnetic fields than the bispectrum. Using current observational limits on CMB non-Gaussianity, the strongest constraints emerge on cosmic magnetic fields. Thus, the CMB trispectrum is a new and powerful probe of primordial magnetism.