Axion inflation with an SU(2) gauge field: detectable chiral gravity waves

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 . It has a negligible effect on the background evolution,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.

Tensor Non-Gaussianity Search: Current Status and Future Prospects

“…A characteristic tensor NG is realized in inflationary models involving the coupling between the axion φ and a gauge field like f (φ) F F , with F and F the gauge field strength tensor and its dual, respectively [7,8,[48][49][50][51]. In this case, the chirality of the gauge field is transferred into the GW sector and hence only the plus mode of GW, h (+2) , survives.…”

Probing P and CP violations on the cosmological collider

“…Existing studies of P-violating bispectra and trispectra [62][63][64][65][66][67][68][69][70][71][72][73][74][75] require the presence of either tensor modes or broken rotational symmetry. These studies are thus aimed to probe the P or CP of the inflaton background or the gravitational interactions.…”

A new mechanism to enhance primordial tensor fluctuations in single field inflation

“…So far, two main approaches have been proposed. The first usually exploits instabilities for additional source fields during inflation: primordial gravity waves can be enhanced by coupling fields driving inflation with additional scalars [29][30][31][32][33][34], U(1) gauge vectors [35][36][37][38][39], non-Abelian vector fields [40][41][42][43][44][45][46][47][48][49][50], or Standard Model fields [51]. The second approach implements space-time symmetry breaking during inflation.…”