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Physics Seminar Date: Thursday, 20 April 2023. Time: 12:15 PM Venue: Lecture Hall 6 Magnetogenesis in non-trivial inflationary scenarios L. Sriram Kumar IIT Madras. 20-04-23 Abstract According to the standard paradigm of primordial magnetogenesis, the seed magnetic fields on cosmological scales are generated during inflation by breaking the conformal invariance of the standard electromagnetic action. This is usually achieved through a non-conformal coupling of the electromagnetic field to the inflation. Also, a parity violating term is often added to the action to generate helical magnetic fields. In this talk, I shall first discuss the effects of deviations from slow roll inflation on the spectra of non-helical as well as helical electromagnetic fields over large and small scales in single field models of inflation. We find that, to generate nearly scale invariant spectra of magnetic fields, even in slow roll inflation, one has to construct non-conformal coupling functions that are dependent on the inflationary model being considered. We show that sharp features in the scalar power spectrum generated due to departures from slow roll inflation inevitably lead to strong features in the power spectra of the electromagnetic fields. Moreover, we show that such effects can also considerably suppress the strengths of the generated electromagnetic fields over the scales of cosmological interest. While it seems possible to undo the strong features that arise in the electromagnetic power spectra in such situations, we point out that it is realized at the cost of severely fine-tuned non-conformal coupling functions. In order to circumvent the challenges that arise in single field models, we consider the generation of magnetic fields in two field models of inflation. We shall illustrate that, in two field models, with suitably chosen non-conformal coupling functions, we can obtain spectra of magnetic fields of the required strength and shape even in situations involving strong departures from slow roll. Lastly, I shall discuss the imprints of the primordial magnetic fields generated in certain two field models on the anisotropies in the cosmic microwave background.
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