Interactions in scalar field cosmology - art. no. 083503

We investigate spatially flat isotropic cosmological models which contain a scalar field with an exponential potential and a perfect fluid with a line ar equation of state. We include an interaction term, through which the ene rgy of the scalar field is transferred to the matter fields, consistent wit h a term that arises from scalar-tensor theory under a conformal transforma tion and field redefinition. The governing ordinary differential equations reduce to a dynamical system when appropriate normalized variables are defi ned. We analyze the dynamical system and find that the interaction term can significantly affect the qualitative behavior of the models. The late-time behavior of these models may be of cosmological interest. In particular, f or a specific range of values for the model parameters there are late-time attracting solutions, corresponding to a novel attracting equilibrium point , which are inflationary and in which the scalar field's energy-density rem ains a fixed fraction of the matter field's energy density. These scalar fi eld models may be of interest as late-time cosmologies, particularly in vie w of the recent observations of the current accelerated cosmic expansion. F or appropriate values of the interaction coupling parameter, this equilibri um point is an attracting focus,and hence as inflating solutions approach t his late-time attractor the scalar field oscillates. Hence these models may also be of importance in the study of inflation in the early universe.