When I studied theoretical physics in the UAM the everybody (well, at least everybody studying he specialty of theoretical physics) favorite teacher was Enrique Álvarez. Possibly, I don't know because I never coincided with him, today Ibañez could discuss the crown, but in that times Ibañez was in CERN and didn't teach.
Particularly great was his course in an asignature devoted to classical mechanics where he explained constrained lagrangian system, and the Dirac way to deal with them. That supposed that I had not any problem in the future understanding quantization of gauge theories, string theories, BRST operators and all that which is a great advantage. Also his course in general relativity was great.
Well, I am happy to see today in arxiv an article of him totally worth to post about: http://arxiv.org/abs/1004.4867
The article makes comments, and insights, on a previous work of Polchinsky the one of the Polchinsky action)in 2007: http://arxiv.org/abs/0709.2899 (I think he talked about that topic in the strings 2008 conferences celebrated in CERN)
The idea is that in de Sitter space the vacuum is not stable in the presence of interactions among particles. I am still reading both articles so I will not comment on them now, but I will edit this post (yes, I promise xD) as soon as I read them and explain what's going on.
But I am sure that some readers of this blog, who also had Álvarez as a teacher, will not wait me and read the article themselves. After all the requisites for reading are mainly some familiarity with basic QFT and quantization on curved spaces. In fact one of the points of this post is to advise them of the existence of the article and so avoid the possibility that they would miss it.