Adding helicity to inflationary magnetogenesis

Abstract

The most studied mechanism of inflationary magnetogenesis relies on the time-dependence of the coefficient of the gauge kinetic term $F_{\mu \nu }{F}^{\mu \nu }$. Unfortunately, only extremely finely tuned versions of the model can consistently generate the cosmological magnetic fields required by observations. We propose a generalization of this model, where also the pseudoscalar invariant $F_{\mu \nu }{\tilde{F}}^{\mu \nu }$ is multiplied by a time dependent function. The new parity violating term allows more freedom in tuning the amplitude of the field at the end of inflation. Moreover, it leads to a helical magnetic field that is amplified at large scales by magnetohydrodynamical processes during the radiation dominated epoch. As a consequence, our model can satisfy the observational lower bounds on fields in the intergalactic medium, while providing a seed for the galactic dynamo, if inflation occurs at an energy scale ranging from $10^5$ to $10^{10}$ GeV. Such energy scale is well below that suggested by the recent BICEP2 result, if the latter is due to primordial tensor modes. However, the gauge field is a source of tensors during inflation and generates a spectrum of gravitational waves that can give a sizable tensor to scalar ratio $r=\mathcal{O}(0.2)$ even if inflation occurs at low energies. This system therefore evades the Lyth bound. For smaller values of $r$, lower values of the inflationary energy scale are required. The model predicts fully helical cosmological magnetic fields and a chiral spectrum of primordial gravitational waves.

17 pages, 4 figures. Minor changes to match the version accepted for publication in JCAP

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Cited by in corpus (13)

• Consistent generation of magnetic fields in axion inflation models
• Universal Constraints on Axions from Inflation
• Parity-violating and anisotropic correlations in pseudoscalar inflation
• Gamma-ray observations of blazars and the intergalactic magnetic field spectrum
• How Well Can We Really Determine the Scale of Inflation?
• A scenario for inflationary magnetogenesis without strong coupling problem
• On the stability and causality of scalar-vector theories
• Implications of a Primordial Magnetic Field for Magnetic Monopoles, Axions, and Dirac Neutrinos
• Parity-odd correlators of diffuse gamma rays and intergalactic magnetic fields
• Magnetic field spectrum at cosmological recombination revisited
• Generation of large-scale magnetic fields, non-Gaussianity, and primordial gravitational waves in inflationary cosmology
• Cosmological consequences of classical flavor-space locked gauge field radiation
• Helical cosmological magnetic fields from extra-dimensions