Flat Cosmology with Coupled Matter and Dark Energy

Three models of a flat universe of coupled matter and dark energies withdifferent low-redshift parameterizations of the dark energy equation of stateare considered. The dark energy is assumed to vary with time like the trace ofthe energy-momentum tensor of cosmic matter. In the radiation-dominated era themodels reduce to standard cosmology. In the matter-dominated era they are, formodern values of the cosmological parameters, consistent with data from SNe Iasearches and with the data of Gurvits et al.(1999)for angular sizes of ultracompact radio sources. We find that the angular size-redshift tests for ourmodels offer a higher statistical confidence than that based on SNe Ia data. Acomparison of our results with a recent revised analysis of angularsize-redshift legacy data is made,and the implications of our models withoptimized relativistic beaming in the radio sources is discussed. In particularwe find that relativistic beaming implies a Lorentz factor less than 6,inagreement with its values for powerful Active Galactic Nuclei.Comment: Version to appear in The Astronomical Journal, with a modified name- Flat Cosmology with Coupled Matter and Dark Energies. Expanded and Modified conten