Planar equivalence in Pisa

I just came back from a visit in Pisa. Augusto Sagnotti invited me to give a colloquium about planar equivalence in Scuola Normale Superiore.
The visit was fantastic: good weather, great food and of course Pisa itself is
an extremely interesting place to visit. (I recommend the old cemetery, which is actually a mini museum, near the tilted tower).
Physics-wise, the talk went very well (almost ...). There were many questions and
I felt that the audience was really interested.
Let me quickly review the topic:
Together with Misha Shifman and Gabriele Veneziano we argued that one-flavor
QCD becomes equivalent to pure N=1 super Yang-Mills, if a certain large-N limit is taken. The large-N limit is not the standard 't Hooft limit, but a limit where the fundamental representation is replaced by the two-index antisymmetric representation. For QCD (an SU(3) gauge theory) the fundamental representation is anyhow equivalent to the antisymmetric representation so this procedure makes sense. The outcome of planar equivalence is several predictions about non-perturbative QCD, among them the value of the quark condensate and a degeneracy in the hadronic spectrum of one-flavor QCD.
There were many questions in the seminar. Some of them about the proof itself but most of them about the implications. An interesting issue is 1/N corrections. It is not clear how to improve our predictions by including contributions beyond the leading large-N one. Overall the atmosphere in the seminar was positive, except an annoying remark by someone who argued that the Nambu-Jona-Lasinio model gives better results. I couldn't understand why the issue was raised and how a model of QCD can compete with results in QCD itself.
Later on I had very good discussions with Patella, Konishi and DiGiacomo, mostly about a check of planar equivalence on the lattice. There were also questions about the validity of the proof and the possibility of charge conjugation breaking, but I will not write about it here. Instead, I will refer whoever is insterested to the paper that we posted today, hep-th/0701229 .

A prize for the Sign Problem

This looks like a good way of getting started this blog. Last July, six of us entered the Gower Bike Ride with a team called (guess what?) "The Sign Problem". Although that was not the primary goal, we won an award for being the group who collected more funds for the British Heart Foundation. The award is in my office, for the lucky of you who get a chance to walk in. At last, one result for the "Sign Problem" :-)