Phenomenology of fermion production during axion inflation

Abstract

We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.

Chiral anomaly, Schwinger effect, Euler-Heisenberg Lagrangian and application to axion inflation

“…This field redefinition never changes the physical result as it should be, which is however has been explicitly shown only in two limited cases: the case without the gauge coupling (uncharged fermions) in Ref. [64,65] and the case without mass in Ref. [9].…”

Baryogenesis from axion inflation

“…Before concluding this section, let us emphasize that the MHD simulations supporting the scaling behavior (39) [see also (B13)] for R m > 1 have not been performed for the initial condition of our interest including large chemical potentials as required by Eq. (42).…”

Searches for other vacua. Part II. A new Higgstory at the cosmological collider

“…In the end, let us comment on the effect of the fermion density on the motion of the inflaton. The fermion density induces a correction to the equation of motion for the inflaton [41]…”

“…This coupling acts like a chemical potential for the broken axial symmetry. Thus, it is not surprising that this term can help with particle production [40,41]. We will work in the framework of effective field theory of inflation [42,43] and we will not specify an inflaton model.…”