On the stability and causality of scalar-vector theories

摘要: Various extensions of standard inflationary models have been proposed recently by adding vector fields. Because they are generally motivated large-scale anomalies, and the possibility statistical anisotropy primordial fluctuations, such require to introduce non-standard couplings between fields on one hand, either gravity or scalar other hand. In this article, we study involving a field coupled field. We derive restrictive necessary conditions for these be both stable (Hamiltonian bounded below) causal (hyperbolic equations motion).