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Friday, February 14th 2020

12:30 pm:

Abstract: In this talk, I will discuss a new Berry phase in the Cosmic Microwave Background (CMB) that is observable today. Very light axions are a generic prediction of string compactification. If cosmic strings associated with these axions were produced in the early universe, they quickly approach a so-called scaling solution, such that strings persist in the sky today. I will present some remarkable signals of such strings coupled to photons. In this string background, there is a new Berry phase: a frequency-independent topological polarization rotation of CMB photons with the polarization rotation angle equal to the fine structure constant up to an undetermined rational number. This manifests itself as a rotation of E-modes in the CMB polarization to B-modes. I will discuss the correlation functions of this polarization rotation and how to compute them both analytically and numerically. I will also discuss how to search for such correlation functions in the CMB with constraints obtained with Planck 2015 data. These strings can also be looked for in position space with Edge Detection techniques in the CMB, as well as with strongly lensed quasar systems. I will show how measuring the undetermined rational number may shed light on the quantization of electric charge in the standard model and how CMB can teach us about Grand Unified Theories.

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