Merry Christmas!
After the arxiv came back from its days off, it spat out 6(!) papers on scattering amplitudes in gauge theories/gravity in one night:
- Scattering Amplitudes and the Positive Grassmannian, a long-awaited paper by Nima Arkani-Hamed and 5 other authors has 153 pages and is the largest physics paper I ever tried to read (besides reviews). Some of results were advertised long before the publication, so we already know that it links together Grassmannians, combinatorics, on-shell recursion relations and Yangian symmetry to get an all-loop integrand for scattering amplitudes in N=4 SYM (and, as it turns out, in theories with less supersymmetries). The interesting topics mentioned in the introduction which I was completely not aware of include relation of on-shell diagrams to cluster algebras and considering 1+1 and 2+1 integrable systems as special cases of the on-shell diagrammatic construction.
- The supersymmetric Penrose transform in six dimensions by L. Mason and R.A. Reid-Edwards.
- From the holomorphic Wilson loop to `d log' loop-integrands for super-Yang-Mills amplitudes by A.E. Lipstein and L. Mason again.
- On Closed Twistor String Theory again by R.A. Reid-Edwards.
- An algebraic approach to BCJ numerators by C. Fu, Y. Du and B. Feng.
- CSW-like Expansion for Einstein Gravity, a humble paper by S. Rajabi, B. Penante and myself. Notice, that while most of the people above calculated amplitudes in SYM, we dealt with Gravity.