Literature of Monday 26th May

I was planning to present this paper by Gasperini

http://arxiv.org/pdf/0805.2330

but Claudio today suggest me to change because it is too much "foggy"

So I'm triyng to prepare a "classical" paper by Weinberg and Witten suggested by Riccardo...I had a fast read to the paper and I had some difficulties in the understanding of technical ditails

I don't know how much deep will be my understanding of the paper because there are only few day to study it... but if you try to read it we can discuss together on monday

Thanks

This is the link to the paper.