Magnetogenesis: Axion Inflation and Gravitational Waves

This lecture discusses the phenomenon of magnetogenesis in the context of axion inflation and its implications for gravitational waves. The instructor begins by introducing the concept of inflation and its significance in cosmology, emphasizing the advantages of axion inflation. The discussion progresses to the allowed couplings of fields with shift symmetry, particularly focusing on gauge fields and their interactions with the inflaton. The instructor explains how gauge fields can lead to density fluctuations and backreaction effects, which are crucial for understanding the dynamics of inflation. The efficiency of reheating is highlighted, showing how coupling the axion to gauge fields can result in explosive energy transfer. The lecture also covers the evolution of helical magnetic fields and their connection to observations, including the potential for primordial black hole formation. The instructor concludes by summarizing the rich phenomenology arising from this simple model of inflation, including implications for baryogenesis and neutrino physics, and the observable consequences of gravitational waves.