Who: Jakob Jark Jørgensen
When: Monday, January 5, 2009
This report comprises two main parts:
The first part is about quantum electrodynamics. The second part is about spontaneous symmetry breaking and the Higgs mechanism. We start out by considering quantum electrodynamics which deals with the interactions between electrons, positrons and photons. We shall obtain the electromagnetic interaction by requiring invariance of the Lagrangian density for the electron-positron field under local U(1) phase transformations. We shall then develop a perturbative theory known as the S-matrix expansion, and use this to derive transition amplitudes for elementary electromagnetic processes. We will see that interactions can be interpreted as being brought about by exchange of virtual intermediate particles.
In the second part of the report we focus on the Higgs mechanism. We start out by explaining the concept of spontaneous symmetry breaking using a simple model. This simple model will be ’gauged’ and we shall apply the Higgs mechanism thereby making the gauge bosons massive, while preserving the gauge symmetry of the theory. In the final section we shall see that the W± and Z0 bosons of the electroweak theory become massice by application of the Higgs mechanism. We shall obtain expressions for the invariant masses of the W±, Z0 and Higgs bosons.