Cosmological consequences of classical flavor-space locked gauge field radiation

Abstract

We propose a classical SU(2) gauge field in a flavor-space locked configuration as a species of radiation in the early universe, and show that it would have a significant imprint on a primordial stochastic gravitational wave spectrum. In the flavor-space locked configuration, the electric and magnetic fields of each flavor are parallel and mutually orthogonal to other flavors, with isotropic and homogeneous stress-energy. Due to the non-Abelian coupling, the gauge field breaks the symmetry between left-and right-circularly polarized gravitational waves. This broken chiral symmetry results in a unique signal: non-zero cross correlation of the cosmic microwave background temperature and polarization, T B and EB, both of which should be zero in the standard, chiral symmetric case. We forecast the ability of current and future CMB experiments to constrain this model. Furthermore, a wide range of behavior is shown to emerge, depending on the gauge field coupling, abundance, and allocation into electric and magnetic field energy density. The fluctuation power of primordial gravitational waves oscillates back and forth into fluctuations of the gauge field. In certain cases, the gravitational wave spectrum is shown to be suppressed or amplified by up to an order of magnitude depending on the initial conditions of the gauge field.

Higgsed Gauge-flation

“…As we demonstrate, the remarkable feature of Higgsed Gauge-flation is the generation of observable gravitational waves at much lower energy scales -in this model, gravitational waves mix with exponentially enhanced gauge field fluctuations, resulting in their subsequent amplification. This phenomena is also observed in Higgsed Chromo-Natural inflation [26] and in models of inflation that have an accompanying spectator Chromo-Natural inflation-like sector [30][31][32] Classical non-Abelian gauge fields lead to striking phenomenology in cosmological settings [33,34], most notably chiral gravitational waves [23,30,31,[35][36][37][38][39][40][41][42][43] and the facilitation of gravitational leptogenesis [44]. Classical non-Abelian gauge fields have also recently been employed in generalized multi-Proca theories [45] to build stable inflationary models that do not require gauge invariance [46], and to generate inflation models with Horndeski couplings [47,48].…”

Gravitational wave–Gauge field oscillations

“…In a scenario in which relic gauge fields contribute a species of dark radiation [13,14], the effect explored in this paper would imprint a novel signature on an inflationary spectrum of primordial gravitational waves. When long wavelength modes enter the horizon and begin to oscillate, a portion of the gravitational wave transforms into a gauge field wave and back again, depending on the relative abundance of the gauge field radiation.…”

“…4 of Ref. [14]. Not only will the gravitational wave spectrum carry a record of the thermal history of the Universe [23], it will also carry the imprint of the gravitational wave -gauge field oscillations.…”

“…The flavor-space locked configuration under this model is stable, as shown through a full cosmological perturbation analysis in Refs. [13,14]. Hence, we find that the gauge field strength tensor F µν has nonzero components where we expect to find an electric field.…”

“…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.…”