Cosmological evolution of a purely conical codimension-2 brane world

We study the cosmological evolution of isotropic matter on an infinitely thinconical codimension-two brane-world. Our analysis is based on the boundarydynamics of a six-dimensional model in the presence of an induced gravity termon the brane and a Gauss-Bonnet term in the bulk. With the assumption that thebulk contains only a cosmological constant Lambda_B, we find that the isotropicevolution of the brane-universe imposes a tuned relation between the energydensity and the brane equation of state. The evolution of the system has fixedpoints (attractors), which correspond to a final state of radiation forLambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, consideringanisotropic matter on the brane, the tuning of the parameters is lifted, andnew regions of the parametric space are available for the cosmologicalevolution of the brane-universe. The analysis of the dynamics of the systemshows that, the isotropic fixed points remain attractors of the system, and forvalues of Lambda_B which give acceptable cosmological evolution of the equationof state, the line of isotropic tuning is a very weak attractor. The initialconditions, in this case, need to be fine tuned to have an evolution withacceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte