Simple fixed-brane gauges in S₁/Z₂ braneworlds

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For five-dimensional braneworlds with an S₁/Z₂ orbifold topology for the extra dimension x⁵, we discuss the validity of recent claims that a gauge exists where the two boundary branes lie at fixed positions and the metric satisfies gμ₅=∂₅ g₅₅=0 where μ labels the transverse dimensions. We focus on models where the bulk is empty apart from a negative cosmological constant, which, in the case of cosmological symmetry, implies the existence of a static frame with Schwarzschild-AdS geometry. Considering the background case with the branes moving apart after a collision, we show that such a gauge can be constructed perturbatively, expanding in either the time after collision or the brane velocity. Finally we examine how cosmological perturbations can be accommodated in such a gauge.