## Apologies

Sorry, sorry and sorry for not posting in weeks. It is sad that there does not seem any time to catch up in the future. A quick summary of what we done so far on my classes:

**Relativity**

We finished the discussion of Yang-Mills theory and then started considering the gauge group for the general coordinate transformations. In turns out that in order to incorporate fermions (spinors) one needs to introduce a local Lorentz transformations. Most of last week was going through Siegel’s notation and writing out the usual identities and expressions for covariant derivatives, torsion and curvature tensors and vierbeins. Yesterday we discussed some gauge choices and some conditions to deal with redundant degrees of freedom (i.e. setting the torsion equal to zero).

**Group theory**

We finally finished with finite group theory and started with Lie groups and algebra. In class we saw how SU(2) is the covering group of SO(3) and we also considered the covering group of the Lorentz group. We listed the classical algebras and hopefully today we will classify all Lie algebras and mention the exceptional algebras.

**Quantum field theory**

Physics is finally creeping back to quantum field theory. We constructed states that have particle interpretations and basically solved the free theory. Today we discussed Green functions for the Klein-Gordon equation. Next Thursday we should treat interacting fields and soon we will start with path integrals.

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