Early-Universe Model Building
  Theoretical investigations into the evolution of the early universe are an
essential part of particle physics that allow us to identify viable extensions
to the Standard Model as well as motivated parameter space that can be probed
by various experiments and observations. In this white paper, we review
particle physics models of the early universe. First, we outline various models
that explain two essential ingredients of the early universe (dark matter and
baryon asymmetry) and those that seek to address current observational
anomalies. We then discuss dynamics of the early universe in models of neutrino
masses, axions, and several solutions to the electroweak hierarchy problem.
Finally, we review solutions to naturalness problems of the Standard Model that
employ cosmological dynamics.
