Cosmic vector for dark energy: Constraints from supernovae, cosmic microwave background, and baryon acoustic oscillations

It has been recently shown that the presence of a vector field over cosmological scales could explain the observed accelerated expansion of the Universe without introducing either new scales or unnatural initial conditions in the early Universe, thus avoiding the coincidence problem. Here, we present a detailed analysis of the constraints imposed by supernova type Ia (SNIa), cosmic microwave background (CMB), and baryon acoustic oscillation (BAO) data on the vector dark energy model with general spatial curvature. We find that contrary to standard cosmology, CMB data exclude a flat universe for this model and, in fact, predict a closed geometry for the spatial sections. We see that CMB and SNIa Gold data are perfectly compatible at the 1-sigma level, however the SNIa Union data set exhibits a 3-sigma tension with CMB. The same level of tension is also found between SNIa and BAO measurements.

Figure 1

Left panel: evolution of energy densities. Dashed (red) for radiation, dotted (green) for matter, and solid (blue) for vector dark energy. We also show for comparison the cosmological constant energy density in dash-dotted line. We see the rapid growth of dark energy contribution at late times approaching the final singularity. Right panel: cosmological evolution of the vector field. In these two plots we see the unimportance of the time at which we set the initial conditions due to the fact that both the vector field and the fraction of dark energy density are constant in the early Universe.

Figure 2

In these plots we show the 68%, 95%, and 99% C.L. regions for BAO (large orange regions on the left part of plots), CMB (long green regions in the upper part), and SNIa (closed blue regions in the center). We show the contours obtained for both the Union data set (left) and the Gold data set (right). The blue line corresponds to a flat universe.

Figure 3

In this plot we show the likelihood obtained from the CMB data set for the vector field model. We can see that a flat universe is clearly ruled out and a closed geometry for the spatial sections is strongly favored.