Vector models of gravitational Lorentz breaking

Dynamical Lorentz symmetry breaking can occur when the dynamics of a tensor field cause it to take on a non-zero expectation value \textit{in vacuo}, thereby providing one or more ``preferred directions'' in spacetime. Couplings between such fields and spacetime curvature will then affect the dynamics of the metric, leading to interesting gravitational effects. Bailey \& Kosteleck\'{y} (2006) developed a PPN-like formalism that, under certain assumptions concerning the field's couplings and stress-energy, allows for the analysis of gravitational effects in the presence of Lorentz symmetry breaking. We systematically investigate which vector models of Lorentz breaking can be successfully analyzed under the Bailey-Kosteleck\'{y} formalism. Implications for the gravitational analysis of specific Lorentz-breaking vector models, including Bekenstein's ``TeVeS'' and Carroll \textit{et al.}'s ``sigma-model {\ae}ther'', are discussed.