Cosmological models with Yang–Mills fields

We discuss cosmological models involving homogeneous and isotropic Yang–Mills (YM) fields. Such models were proposed recently as an alternative to scalar models of cosmic acceleration. There exists a unique $\mathrm{SU}(2)$ YM configuration (generalizable to larger gauge groups) whose energy–momentum tensor is homogeneous and isotropic in space. It is parameterized by a single scalar field with a quartic potential. In the case of the closed universe the coupled YM–doublet Higgs system admits homogeneous and isotropic configurations as well. While pure Einstein–Yang–Mills (EYM) cosmology with the standard conformally invariant YM action gives rise to the hot universe, Einstein–Yang–Mills–Higgs (EYMH) cosmology has a variety of regimes which include inflationary stages and bounces, and exhibits global cycling behavior reminiscent of the multiverse developed in time. We also discuss other mechanisms of conformal symmetry breaking such as the string-inspired Born–Infeld (BI) modification of the YM action or field-theoretical quantum corrections.