Friday, November 22, 2013
11:00 am

High Energy Theory Seminar

Scattering Amplitudes, Unitarity, and the Positive Grassmannian
Jacob Bourjaily, Harvard

In recent years, a complete reformulation of perturbative quantum field theory has been found for certain theories. Although a similar reformulation is likely to exist for any quantum field theory, it is exceptionally simple in the case of planar, maximally supersymmetric Yang-Mills. I will (briefly) review this new formulation, describing the connections between certain field-theoretic quantities called  `on shell diagrams' and a space known as the `positive Grassmannian', how both can be characterized combinatorially, and how the entire S-matrix can be defined in terms of these combinatorial objects. I will then describe how these ideas can be applied to teach us about multi-loop amplitudes, and show some of the surprising new features that appear at 2-loops and beyond, even in the case of planar N=4 super Yang-Mills.

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