Adding helicity to inflationary magnetogenesis

By C. Caprini, L. Sorbo. 2014

148 citations recorded by the source corpus.

The most studied mechanism of inflationary magnetogenesis relies on the time-dependence of the coefficient of the gauge kinetic term Fμν Fμν. 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 Fμν F̃μν 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 105 to 1010 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=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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/87d70f386ab8325e3795038f4638f250b0f7c2f5

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Citations in the corpus

Scale-dependent gravitational waves from a rolling axion (2015, background): “(5)The phenomenological constraints on the production of chiral magnetic fields and their subsequent sourcing of chiral gravitational waves have been studied in [39, 40].”
Magnetogenesis from axion inflation (2016, background): “[44], which is a hybrid between the Ratra and axion model, helical magnetic fields are produced during inflation.”