I have read (mainly in the articles of Atiyah) that the partition function is the simplest topological invariant of a quantum field theory.
I have an arithmetic geometry background and know statistical physics quite well, but am a beginner in QFT. A reference for details on the above statement in mathematical language à la "Quantum Fields and Strings: A Course for Mathematicians" would be highly appreciated.
A sketch of the ideas involved would be even nicer.
If this question is too simple or vague, please let me know - I will transfer it to SE.