Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission

The original work presented in this thesis constitutes an important contribution to modern Cosmic Ray (CR) physics, and comes during one of the most exciting periods of this field.
The first part introduces a new numerical code (DRAGON) to model the CR propagation in our Galaxy. The code is then used to perform a combined analysis of CR data, making it possible to determine their propagation properties with unprecedented accuracy.
The second part is dedicated to a theoretical interpretati...