Gauge-flation confronted with Planck

Abstract

Gauge-flation is a recently proposed model in which inflation is driven solely by a non-Abelian gauge field thanks to a specific higher order derivative operator. The nature of the operator is such that it does not introduce ghosts. We compute the cosmological scalar and tensor perturbations for this model, improving over an existing computation. We then confront these results with the Planck data. The model is characterized by the quantity γ ≡H 2 (where g is the gauge coupling constant, Q the vector vev, and H the Hubble rate). For γ < 2, the scalar perturbations show a strong tachyonic instability. In the stable region, the scalar power spectrum n s is too low at small γ, while the tensor-to-scalar ratio r is too high at large γ. No value of γ leads to acceptable values for n s and r, and so the model is ruled out by the CMB data. The same behavior with γ was obtained in Chromo-natural inflation, a model in which inflation is driven by a pseudo-scalar coupled to a non-Abelian gauge field. When the pseudo-scalar can be integrated out, one recovers the model of Gauge-flation plus corrections. It was shown that this identification is very accurate at the background level, but differences emerged in the literature concerning the perturbations of the two models. On the contrary, our results show that the analogy between the two models continues to be accurate also at the perturbative level.

Gravitational wave–Gauge field oscillations

“…We follow the notation in Ref. [13][14][15][16], where the behavior of the coupled system for N = 1 was studied in the context of inflation and other cosmological scenarios. We consider weak distortions of the spacetime metric and the gauge field, δg µν = a 2 h µν and δ A µ · e ν = ay µν , where h µν , y µν are transverse, traceless, and synchronous.…”

Chiral imprint of a cosmic gauge field on primordial gravitational waves

“…[12,13] that are invariant under generalized covariance and SU(2) gauge transformations. The equations of motion for the Fourier amplitudes of a right circularly polarized gravitational wave traveling in the +z direction, and the corresponding gauge field fluctuation, are given by…”

Generation of large-scale magnetic fields, non-Gaussianity, and primordial gravitational waves in inflationary cosmology

“…The back reaction problem by the generation of electromagnetic fields during inflation has been found [10,[64][65][66][67][68] (for more recent related works on the relation between the generated gauge fields and inflation, see [69][70][71][72][73][74]). It has been pointed out [64] that the amplitude of the current magnetic fields on O(1) Mpc scale should be less than 10 −32 G. In such a case, the dynamics of inflation is not disturbed by the back reaction originating from the generation of electromagnetic fields.…”