Structure of structure formation theories - art. no. 083509

We study the general structure of models for structure formation, with appl ications to the reverse engineering of the model from observations. Through a careful accounting of the degrees of freedom in covariant gravitational instability theory, we show that the evolution of structure is completely s pecified by the stress history of the dark sector. The study of smooth, ent ropic, sonic. scalar anisotropic, vector anisotropic, and tensor anisotropi c stresses reveals the origin, robustness, and uniqueness of specific model phenomenology. We construct useful and illustrative analytic solutions tha t cover cases with multiple species of differing equations of state relevan t to thr current generation of models, especially those with effectively sm ooth components. We present a simple case study of models with phenomenolog ies similar to that of a Lambda CDM model to highlight reverse-engineering issues. A critical-density universe dominated bl: a single type of dark mat ter with the appropriate stress history can mimic a Lambda CDM model exactl y. [S0556-2821(99)04208-3].