High Energy Physics

The observed conservation of Baryon and Lepton number may arise because they are gauge symmetries. Models are discussed where Baryon and lepton number are the charges for a spontaneously broken U(1) gauge symmetries. The best of these models is: (1) free of Landau poles that are near the weak scale, (2) has no flavor changing neutral currents at tree level and (3) contains a dark matter candidate.

Throughout history science has aimed at unification, whereby more phenomena are explained by more fundamental theories with simpler principles. We will discuss how string theory aims at being the ultimate unified theory of all elementary forces in nature.

Galaxy clusters are the biggest gravitationally bound structures in the Universe. Simple features of these objects can help us reconstruct the initial conditions at the Big-Bang and test the fundamental laws of physics.

The Large Hadron Collider was recently switched on, then broke and was switched on again. It has started producing collisions that probe Nature on the smallest distances yet reached. What broke when it was switched on? How does one detect what comes out of these collisions, and what can the result tell us about how Nature works on these scales? This talk briefly describes what we think we know, why it may be wrong, and whether (in either case) it will destroy the world.