“School of Physic”
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| Paper IPM / Physic / 14325 |
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| Abstract: | |
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We study a single field axion inflation model in the presence of an SU(2) gauge field with a small vev.
In order to make the analysis as model-independent as possible, we consider an arbitrary potential for the axion that is able to support the slow-roll inflation. The gauge field is coupled to the axion with a Chern-Simons interaction [(λ)/(f)]Fμνa~Faμν where [(λ)/(f)] ∼ [(O(10))/(\mpl )]. It has a negligible effect on the background evolution, [(ρYM)/(\mpl2H2)] <~ϵ2. However, its quantum fluctuations make a significant contribution to the cosmic perturbation.
In particular, the gauge field has a spin-2 fluctuation which explicitly breaks the parity between the left- and right-handed polarization states. The chiral tensor modes are linearly coupled to the gravitational waves and lead to a circularly polarized tensor power spectrum comparable to the unpolarized vacuum power spectrum.
Moreover, the scalar sector is modified by the linear scalar fluctuations of the gauge field. Since the spin-0 and spin-2 fluctuations of the SU(2) gauge field are independent, the gauge field can, at the same time, generate a detectable chiral gravitational wave signal and have a negligible contribution to the scalar fluctuations, in agreement with the current CMB observations.
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