Probing the coupling between dark components of the universe

Abstract

We place observational constraints on a coupling between dark energy and dark matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the five-year Supernova Legacy Survey (SNLS), the cosmic microwave background (CMB) shift parameter from the three-year Wilkinson Microwave Anisotropy Probe (WMAP), and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). The interactions we study are (i) constant coupling $\ensuremath{\delta}$ and (ii) varying coupling $\ensuremath{\delta}(z)$ that depends on a redshift $z$, both of which have simple parametrizations of the Hubble parameter to confront with observational data. We find that the combination of the three databases marginalized over a present dark energy density gives stringent constraints on the coupling, $\ensuremath{-}0.08<\ensuremath{\delta}<0.03$ (95% C.L.) in the constant coupling model and $\ensuremath{-}0.4<{\ensuremath{\delta}}_{0}<0.1$ (95% C.L.) in the varying coupling model, where ${\ensuremath{\delta}}_{0}$ is a present value. The uncoupled $\ensuremath{\Lambda}\mathrm{CDM}$ model (${w}_{X}=\ensuremath{-}1$ and $\ensuremath{\delta}=0$) still remains a good fit to the data, but the negative coupling ($\ensuremath{\delta}<0$) with the equation of state of dark energy ${w}_{X}<\ensuremath{-}1$ is slightly favored over the $\ensuremath{\Lambda}\mathrm{CDM}$ model.