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arXiv · 0812.1050

Sigma-Model Aether

Sean M. Carroll·Timothy R. Dulaney·Moira I. Gresham·Heywood Tam
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Abstract

Theories of low-energy Lorentz violation by a fixed-norm "aether" vector field with two-derivative kinetic terms have a globally bounded Hamiltonian and are perturbatively stable only if the vector is timelike and the kinetic term in the action takes the form of a sigma model. Here we investigate the phenomenological properties of this theory. We first consider the propagation of modes in the presence of gravity, and show that there is a unique choice of curvature coupling that leads to a theory without superluminal modes. Experimental constraints on this theory come from a number of sources, and we examine bounds in a two-dimensional parameter space. We then consider the cosmological evolution of the aether, arguing that the vector will naturally evolve to be orthogonal to constant-density hypersurfaces in a Friedmann-Robertson-Walker cosmology. Finally, we examine cosmological evolution in the presence of an extra compact dimension of space, concluding that a vector can maintain a constant projection along the extra dimension in an expanding universe only when the expansion is exponential.

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Sean M. Carroll, Timothy R. Dulaney, Moira I. Gresham, Heywood Tam. 2009-01-16. Sigma-Model Aether. https://doi.org/10.1103/physrevd.79.065012

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