Abstract
We investigate axion inflation where the gravitational Chern–Simons term is coupled to a periodic function of the inflaton. We find that tensor perturbations with different polarizations are amplified in different ways by the Chern–Simons coupling. Depending on the model parameters, the resonance amplification results in a parity-violating peak or a board plateau in the energy spectrum of gravitational waves, and the sharp cutoff in the infrared region constitutes a characteristic distinguishable from stochastic gravitational wave backgrounds produced by matter fields in Einstein gravity.
Highlights
The parameter resonance amplification of scalar perturbations during inflation has been widely discussed [13,14,15,16,17]
We investigate the similar amplification of tensor perturbations with parity-violation caused by the gravitational Chern–Simons term coupled to an axion field that drives inflation while they are deep inside the horizon during inflation
We have investigated the amplification of the parity-violating tensor perturbations during axion inflation with the gravitational Chern–Simons coupling
Summary
The parameter resonance amplification of scalar perturbations during inflation has been widely discussed [13,14,15,16,17]. Detecting the sharp infrared cutoff of the GW energy density provides an important clue to the Chern–Simons coupling, as well as extra dimensions predicted in string theory. This resonance peak might be observed by ground-based and space-. Note that the Chern–Simons coupling between an axion field and the gauge fields could trigger the exponential production of helically polarized gauge bosons by the polarization-dependent resonance during the inflation and the post-inflationary preheating [37–46] These helical gauge bosons can source a polarized spectrum of GWs [40,42,46].
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