Holographic dark energy in braneworld models with a Gauss–Bonnet term in the bulk. Interacting behavior and the w=−1 crossing

We apply bulk holographic dark energy in general braneworld models with a Gauss-Bonnet term in the bulk and an induced gravity term and a perfect fluid on the brane. Without making any additional assumptions we extract the Friedmann equation on the physical brane and we show that a -_ coupling arises naturally by the full 5D dynamics. The low-energy (late-time) evolution reveals that the effective 4D holographic dark energy behaves as ``quintom'', that is it crosses the phantom divide w=-1 during the evolution. In particular, the Gauss-Bonnet contribution decreases the present value of w_, while it increases the growing rate of w_ (z) with z, in comparison with the case where such a term is absent.