Oscillating and Static Universes from a Single Barotropic Fluid

Abstract

We consider cosmological solutions to general relativity with a single barotropic fluid, where the pressure is a general function of the density, $p=f(\rho )$. We derive conditions for static and oscillating solutions and provide examples, extending earlier work to these simpler and more general single-fluid cosmologies. Generically we expect such solutions to suffer from instabilities, through effects such as quantum fluctuations or tunneling to zero size. We also find a classical instability ("no-go" theorem) for oscillating solutions of a single barotropic perfect fluid due to a necessarily negative squared sound speed.

5 pages; v2: additional references, minor clarification in Sec. IIC, matches version published in JCAP

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• Vector dark energy models with quadratic terms in the Maxwell tensor derivatives