Axion Strings in the Sky

Jun 28, 2021, 1:40 PM


Prateek Agrawal


I will present some remarkable signals of axion strings coupled to photons. There are compelling theoretical motivations to expect axion strings that persist in the sky today. There is a model-independent polarization rotation of CMB photons in the string background, equal to $\alpha_{em}$ up to a rational number related to the fundamental unit of electromagnetic charge. This manifests itself as a rotation of E-modes in the CMB polarization to B-modes. The current CMB experimental sensitivity to this rotation is about 1%, with many orders of magnitude improvement expected for future experiments. As these strings pass through galactic magnetic fields, they build up localized charge and current density traveling along the string. This sets up a cosmological plasma collider where collisions can occur at very high energies and produce spectacular astrophysical signals.

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