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Topological quantum field theory.

19 votes

What are D-branes, really?

I'm going to attempt a short, partial answer written for pure mathematicians. The word "brane" in high-energy physics means "submanifold". The word is short for "membrane". More precisely, it means …
Greg Kuperberg's user avatar
15 votes

When is a TQFT the dimensional reduction of a higher dimensional TQFT?

Asking for sufficient conditions that an $n$-dimensional TQFT lifts to $n+1$ dimensions is like asking for sufficient conditions that an egg will hatch into a bird. You might think of necessary condi …
Greg Kuperberg's user avatar
49 votes
Accepted

Why are fusion categories interesting?

Fusion categories (over $\mathbb{C}$) are a natural generalization of finite groups and their behavior over $\mathbb{C}$. The complex representation theory of a finite group is a fusion category, but …
10 votes

What do decategorification and "compactification on a circle" have to do with each other?

If you think of a TQFT as a functor from cobordisms to vector spaces, then $F(X \times S^1)$ will give you the dimension of the state space of $X$ (or the superdimension or whatever), because it is th …
Greg Kuperberg's user avatar
14 votes

What's the right way to think about "anomalies" in 3d TQFTs?

My own understanding of anomalies in TQFTs: In cases that I have seen, "anomaly" in general refers to central extensions and line bundles. Physicists have long thought of these issues in a very expl …
Greg Kuperberg's user avatar