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Particle production during Axion Inflation

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If you have a question about this talk, please contact Francesco Coradeschi.

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Identifying the particle driving cosmic inflation as a pseudoscalar (i.e. an axion-like particle) provides a naturally flat direction in field space along which slow-roll inflation may proceed. The rich phenomenology of this model includes an enhanced chiral graviational wave spectrum as well as strong particle production during inflation. In particular, in the presence of a chiral anomaly, there is a dual production of helical Abelian gauge fields and chiral fermions through the Chern-Simons coupling to the inflaton. The motion of the inflaton induces a tachyonic instability for one of the two helicities of the gauge field. The resulting helical gauge field necessarily leads to the production of chiral fermions by deforming their Fermi sphere into discrete Landau levels. The population of the lowest Landau level leads to a chiral asymmetry as inferred from the chiral anomaly, while the higher levels are populated symmetrically through pair production. From the backreaction of the fermions on the gauge field production we derive a conservative but stringent upper bound on the magnitude of the gauge fields. This significantly impacts the predictions for the scalar and tensor power spectra of axion inflation and may also have far-reaching consequences for leptogenesis and the generation of primordial magnetic fields.

This talk is part of the HEP phenomenology joint Cavendish-DAMTP seminar series.

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