# Student Colloquium, Erik Holm Steenberg

*Supervisor: Nikolaj Zinner*

Titel: Gauge theory, behind the standard model.

The standard model has been called the most successful theory in physics. It is capable of explaining three of the four fundamental forces, electro-magnetism, the weak and strong interactions.

But what is the standard model? When people talk about the standard model, you might hear things like "the standard model is U(1)xSU(2)xSU(3)" or Quantum Electrodynamics is a U(1) gauge theory", but what does that mean?

The purpose of this colloquium will be to explain what a gauge theory actually is.

I will start out with gauge in electrodynamics, I will then go to the Schrödinger equation and apply gauge invariance. Then I will go through what a gauge theory is, apply it to the Dirac Lagrangian and show how local phase invariance, U(1) gauge, leads to quantum eletrodynamics. I will then finish off by briefly talking about some of the more advanced gauge theories and one of the results of these, the concept of asymptotic freedom.