paper

A regime of linear stability for the Einstein-scalar field system with applications to nonlinear Big Bang formation

arXiv:1407.6293 · doi:10.4007/annals.2018.187.1.2

Abstract

We linearize the Einstein-scalar field equations, expressed relative to constant mean curvature (CMC)-transported spatial coordinates gauge, around members of the well-known family of Kasner solutions on . The Kasner solutions model a spatially uniform scalar field evolving in a (typically) spatially anisotropic spacetime that expands towards the future and that has a "Big Bang" singularity at . We place initial data for the linearized system along and study the linear solution's behavior in the collapsing direction . Our first main result is the proof of an approximate monotonicity identity for the linear solutions. Using it, we prove a linear stability result that holds when the background Kasner solution is sufficiently close to the Friedmann-Lema\^ıtre-Robertson-Walker (FLRW) solution. In particular, we show that as , various time-rescaled components of the linear solution converge to regular functions defined along . In addition, we motivate the preferred direction of the approximate monotonicity by showing that the CMC-transported spatial coordinates gauge can be viewed as a limiting version of a family of parabolic gauges for the lapse variable; an approximate monotonicity identity and corresponding linear stability results also hold in the parabolic gauges, but the corresponding parabolic PDEs are locally well-posed only in the direction . Finally, based on the linear stability results, we outline a proof of the following result, whose complete proof will appear elsewhere: the FLRW solution is globally nonlinearly stable in the collapsing direction under small perturbations of its data at .

73 pages

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