Axion Inflation with an SU(2) Gauge Field: Detectable Chiral Gravity Waves

Azadeh Maleknejad

doi:10.1007/JHEP07(2016)104

paper

Axion Inflation with an SU(2) Gauge Field: Detectable Chiral Gravity Waves

arXiv:1604.03327 · doi:10.1007/JHEP07(2016)104

Abstract

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 $\frac{λ}{f} F_{μν}^{a} F ~_{a}^{μν}$ where $\frac{λ}{f} \sim O (10)$ . It has a negligible effect on the background evolution, $\frac{ρ _{_{YM}}}{M _{Pl}^{2} H ^{2}} ≲ ε^{2}$ . 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.

34 pages, 8 figures, to appear in JHEP

Axion Inflation with an SU(2) Gauge Field: Detectable Chiral Gravity Waves

Abstract

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