Causality, initial conditions, and inflationary magnetogenesis

TL;DR

This paper explores how causality and the nature of cosmological transitions influence the evolution of inflationary magnetic fields, potentially leading to stronger residual fields that can seed galactic magnetism.

Contribution

It highlights the importance of causality and transition dynamics in post-inflationary magnetic field evolution, challenging previous assumptions about magnetic decay and seed field strength.

Findings

Causality prevents magnetic fields from freezing into matter until horizon re-entry.

Transition details determine the large-scale magnetic evolution after inflation.

Residual magnetic fields can be stronger than previously thought, aiding galactic dynamo processes.

Abstract

The post-inflationary evolution of inflation-produced magnetic fields, conventional or not, can change dramatically when two fundamental issues are accounted for. The first is causality, which demands that local physical processes can never affect superhorizon perturbations. The second is the nature of the transition from inflation to reheating and then to the radiation era, which determine the initial conditions at the start of these epochs. Causality implies that inflationary magnetic fields dot not freeze into the matter until they have re-entered the causal horizon. The nature of the cosmological transitions and the associated initial conditions, on the other hand, determine the large-scale magnetic evolution after inflation. Put together, the two can slow down the adiabatic magnetic decay on superhorizon scales throughout the universe's post-inflationary evolution and thus lead to considerably stronger residual magnetic fields. This is "good news" for both the conventional and the non-conventional scenarios of cosmic magnetogenesis. Mechanisms operating outside standard electromagnetism, in particular, do not need to enhance their fields too much during inflation, in order to produce seeds that can feed the galactic dynamo today. In fact, even conventionally produced inflationary magnetic fields might be able to sustain the dynamo.