Vector fields in cosmology

Vector fields can arise in the cosmological context in different ways, and we discuss both abelian and nonabelian sector. In the abelian sector vector fields of the geometrical origin (from dimensional reduction and Einstein–Eddington modification of gravity) can provide a very non-trivial dynamics, which can be expressed in terms of the effective dilaton-scalar gravity with the specific potential. In the non-abelian sector we investigate the Yang–Mills SU(2) theory which admits isotropic and homogeneous configuration. Provided the nonlinear dependence of the lagrangian on the invariant Fμν F̃ μν , one can obtain the inflationary regime with the exponential growth of the scale factor. The effective amplitudes of the ‘electric’ and ‘magnetic’ components behave like slowly varying scalars at this regime, what allows the consideration of some realistic models with non-linear terms in the Yang–Mills lagrangian.