#### High Energy Theory Seminar- IAS - Simon Caron-Huot, IAS/Copenhagen - “Regge Theory: Old and New”

Regge theory is the idea that physical observable in quantum theory can be defined for complex angular momentum.Its main result is the possibility to analyze an amplitude in one channel, in terms of the states exchanged in another channel, in regimes where the corresponding partial wave expansion would otherwise diverge. I will argue that this result is as relevant today as it was at the time of its discovery.To illustrate the basic principle in a concrete example, I will present an unorthodox derivation of the hydrogen atom spectrum by computing a scattering amplitude in the ultrarelativistic limit.In the very special case where the particles making up this hydrogen-like atom happen to be W-bosons in planar N=4 super Yang-Mills, this derivation gives a new connection with a known integrable system, which should allow the spectrum of their bound states to be calculated at all values of the coupling. As a second example, I will discuss how recent results on the collinear expansion of massless amplitudes, also in N=4, allow for a complete description of the complex angular momentum, which turns out to be surprisingly simple and similar the so-called rapidity plane of integrability.

**Location:**
Bloomberg Lecture Hall - Institute for Advanced Study

**Date/Time: **03/28/14
at
1:30 pm
- 03/28/14
at
2:30 pm

**Category: **High Energy Theory Seminar

**Department: **Physics