#### Theoretical Particle Physics (TPP) is the area of high energy particle physics that seeks to form a coherent picture of all of the data that is available and to develop ideas of what to look for.

Theoretical particle physics is the study of how to describe nature with mathematical precision. It synthesises the knowledge of fundamental particles and interactions gained from experiment and observation into mathematical theories, providing imaginative insights into the conceptual basis of the real world and calculating tools for deriving experimental observables. Through hot big bang cosmology and high-energy astrophysics, theoretical particle physicists also work on understanding the universe at large and the high-energy processes taking place within it.

The prosaically named 'standard model' of particle physics is the current best theory for the fundamental structure of matter. It describes the results of essentially all terrestrial experiments in high-energy physics to a very high level of precision. Its conceptual basis lies in symmetries, group theory and relativistic quantum field theory. Apart from the quantum feature, it is conceptually related to how Einstein's general theory of relativity describes gravitation and the expanding universe. There is hope that particle physics and gravitation may some day be understood within a unified framework, with superstring or M-theory providing a candidate.

However, it is perfectly clear that the standard model of particle physics, despite its great success, is incomplete. It must be extended to accommodate the recent experimental proof that elementary particles called neutrinos have mass. Theorists are currently exploring the many ways this can be done to guide experimentalists in their search to uncover what this new physics actually is. It also cannot explain dark matter, which is about five times as important as ordinary matter in terms of the energy budget of the universe. The dark matter problem proves that quite dramatic new physics must exist, and that the standard model will soon be replaced by a bigger and better theory. The standard model provides no rationale for why the universe is full of matter but only minute amounts of antimatter. Even without these observational proofs that new physics is needed, theoretical shortcomings within the standard model itself have long been argued to motivate the existence of a grander theory. Ideas such as supersymmetry, extra dimensions of space, extended symmetries and new interactions and particles are all being analysed to resolve the deep mysteries posed by Nature itself and the mathematical basis of the standard model.

Theoretical particle physicists within CoEPP work with their experimental colleagues to forge a new and more profound understanding of how nature works at the most fundamental level. We imagine new worlds and invent new ideas, in the ultimate creative activity: trying to fathom what makes nature tick!