Accelerating cosmologies from exponential potentials

Abstract

An exponential potential of the form V ∼ exp(−2cφ/Mp) arising from the hyperbolic or flux compactification of higher-dimensional theories is of interest for getting short periods of accelerated cosmological expansions. Using a similar potential but derived for the combined case of hyperbolic–flux compactification, we study the four-dimensional flat (and open) FLRW cosmologies and give analytic (and numerical) solutions with exponential behaviour of scale factors. We show that, for the M-theory motivated potentials, the cosmic acceleration of the universe can be eternal if the spatial curvature of the 4d spacetime is negative, while the acceleration is only transient for a spatially flat universe. We also briefly comment on the size of the internal space and its associated geometric bounds on massive Kaluza–Klein excitations.