where k is some constant, and η has "−+++" metric signature. This space has boundaries at y = 1/ k and y = 1/(Wk), with 0 ≤ ≤ 1 / k ≤ ≤ 1 / ( W k ) , where k is around the Planck scale, W is the warp factor, and Wk is around a TeV. The boundary at y = 1/ k is called the Planck brane, and the boundary at y = 1/(Wk) is called the TeV brane. The particles of the standard model reside on the TeV brane. The distance between both branes is only −ln(W)/ k, though.