The origin of magnetic fields during inflation: helicity and a sawtooth coupling

• Chiara Cecchini (University of Trento & Trento Institute for Fundamental Physics and Applications TIFPA-INFN)

The origin of large-scale magnetic fields in the Universe is one of the long-standing problems in cosmology. An intriguing possibility is that they are remnants of primordial fields that originated during inflation as amplification of quantum vector perturbations. We discuss the generation of helical magnetic fields by considering a departure from Maxwell's theory during inflation: the electromagnetic sector is coupled to a time-dependent function with a sharp feature, hence the name sawtooth coupling. Scale-invariant modified gravity is a suitable framework for testing the model, providing a natural physical interpretation. We show that strong coupling and back-reaction problems are avoided. Further, this model predicts fully helical magnetic fields compatible with the current observational window of the Intergalactic Medium.