# Theoretical High Energy Physics

One of the great successes of twentieth century physics was that all the forces in nature, however diverse they might appear, were reduced to only four fundamental interactions. Three of those, the electro-magnetic, the weak and the strong forces, are very well understood. Together they constitute what is known as the Standard Model of particle physics - whose final verification was achieved with the discovery of the Brout-Englert-Higgs particle at CERN in 2012. The force which is most familiar to us, the gravitational force, is also the least understood one! Thanks to Einstein, we do have a very good classical description of gravity: the theory of general relativity. While it works very well at larger distances, we expect that quantum mechanical effects come into play when studying gravity at tiny scales. However, general relativity and quantum mechanics turn out to be hard to reconcile. So then a fundamental question is what is the quantum theory of gravity? Answering this question is essential in order to tackle some of the biggest puzzles in physics, related to black holes and the big bang. The leading proposal for a theory of quantum gravity is string theory (links to introductions to string theory can be found below).

One key research direction of the VUB Theoretical High Energy Physics group involves formal theoretical research on fundamental problems in gravity and/or quantum field theory, often in the framework of string theory. Topics of current interest along these lines include dualities and the geometry of string theory; holography, quantum entanglement and the emergence of spacetime; and black holes, thermalization, quantum chaos and complexity.

In recent years the group has also put a particular effort in developing lines of research which would connect more formal ideas with experiments and observations. Our group has been involved in cosmology, the search for physics beyond the standard model at accelerators, and gravitational wave physics.