Flux Tubes

Recent years have witnessed unprecedented progress in the study of (supersymmetric) gauge theories. Among all the exciting developments, two parallel lines of research have been conducted, almost independently, for both confining and non-confining theories using very similar techniques; namely, the integrable structures underlying the dynamics of colour flux tubes. These flux tubes stand as the most stringy degrees of freedom of gauge theories and are believed to be the right variables for unveiling their most nonperturbative aspects, be them confining or not. On the non-confining side of the story, integrability has emerged as one of the most powerful and promising tool for solving the maximally supersymmetric version of the Yang-Mills theory. When applied to the study of the flux-tube dynamics, in the limit of a large number of colours, this technique has led to the non-perturbative determination of a variety of observables. Null polygonal Wilson loops stand out among them all. Not only do they admit a very nice interpretation in terms of flux tubes stretching from one edge of the loops to the other and evolving as dictated by the geometry of these loops, but also happen to be dual to gluons scattering amplitudes -- which are observables of primordial interest in any gauge theories. Despite the many recent progress in taming the dynamics of these flux tubes, their study is still is its infancy and many open questions remain. One of the most pressing and important issue, which we hope to address during the workshop, is whether a system of Thermodynamical Bethe Ansatz equations, akin to the one governing the spectral problem of non-confining (and confining!) gauge theories, exists for the scattering amplitudes / Wilson loops -- and this regardless of the tension, i.e., of the value of the 't Hooft coupling. On the confining side of the story, an impressive amount of high-quality lattice data on the properties of flux
tubes has been collected over the past decade. However, until recently, the interpretation of this data has remained problematic -- mostly because existing theoretical techniques for calculating flux tube spectra were highly inaccurate for the relatively
short flux tubes probed on the lattice. The situation changed drastically over the last few years. The two major ingredients leading to this progress are the full use of non-linearly realized Poincare symmetry and the application of powerful techniques based on
(approximate) integrability for calculating the spectrum. This allowed to identify the first massive excitation on the world sheet of the confining string and paved the way for a comprehensive study of the world sheet dynamics based on lattice data. The goal of this informal meeting will be to assess the current status of these rapidly evolving fields by bringing together experts working in both camps, stimulating discussions and provoking cross-fertilization of ideas. We also look forward to hosting discussions on other exciting recent developments. We anticipate having 10 to 20 participants and will have two discussion sessions every day, one in the morning and the other in the afternoon. Each session will start with one review talk without time constraint and will continue into an informal discussion led by the speaker.