The Nexus between Cosmology and Elementary Particle Physics: Testing Theoretical Speculations through Observations of the Cosmic Microwave Background Anisotropies

The origin of the large scale structure in the universe — galaxies, quasars, clusters, voids, sheets — is one of the most important questions in cosmology. One can show that some non-thermal energy density fluctuations must have been present in the early universe. These fluctuations grew by gravitational instability to form the observed structures. There are at present two families of models to explain the origin of these initial fluctuations: inflationary models and topological defect scenarios. Current observational developments provide a link with theoretical predictions, allowing us to test our theoretical models. In this contribution, I present a sketch of the current status of the origin of cosmological structure formation.