Magnetic fields as a probe of the first microseconds

The primordial magnetic field can be traced in an evolutionary diagram
of comoving magnetic field strength versus comoving length scale, where
it follows a characteristic path. Relating the start- and endpoints to
each other is an important theoretical accomplishment. At the same time,
observational constraints in radio and gamma ray frequencies begin to
narrow down the allowed parameter space in this evolutionary diagram. I
will highlight several of the theoretical and observational discoveries
that make primordial magnetic fields and gravitational waves powerful
probes of the first microseconds of the universe, when important beyond
standard model physics processes have occurred.