For open FLRW universes in two-scalar exponential-potential models from 10d IIA supergravity, the late-time attractor sets the effective exponent to the shortest vector to the convex hull of potential exponents, giving small g_s and alpha' corrections and scale separation in most models.
Collapsing universe before time
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abstract
In this note, we prove analytic bounds on the equation of state of a cosmological fluid composed of an arbitrary number of canonical scalars evolving in a negative multi-exponential potential. Because of the negative energy, the universe is contracting and eventually undergoes a big crunch. A contracting universe is a fundamental feature of models of ekpyrosis and cyclic universes, which are a proposed alternative to cosmic inflation to solve the flatness and horizon problems. Our analytic bounds set quantitative constraints on general effective theories of ekpyrosis. When applied to specific top-down constructions, our bounds can be used to determine whether ekpyrosis could in principle be realized. We point out some possible sources of tension in realizing the ekpyrotic universe in controlled constructions of string theory.
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Universal Cosmologies
For open FLRW universes in two-scalar exponential-potential models from 10d IIA supergravity, the late-time attractor sets the effective exponent to the shortest vector to the convex hull of potential exponents, giving small g_s and alpha' corrections and scale separation in most models.