Conformally Coupled Tachyonic Dark Energy

Abstract

We present and study a conformally coupled dark energy model, characterised by an interaction between a tachyon field $\phi$, with an inverse square potential $V (\phi)$, and the matter sector. A detailed analysis of the cosmological outcome reveals different possibilities, in contrast with the previously studied uncoupled model, for which there exists only one stable critical point that gives late-time acceleration of the Universe. The introduction of the coupling translates into an energy exchange between the fluids. We find the interesting possibility of the emergence of a new fixed point, which is a scaling solution and an attractor of the system. In this case, it is possible to describe an everlasting Universe with $\Omega_{\phi} \simeq 0.7$, therefore alleviating the cosmic coincidence problem. However, we find that, in order for the evolution to be cosmologically viable, there is the need to introduce one uncoupled matter species, dominant at early times.