The generalized Wilson loop operator interpolating between the supersymmetric and the ordinary Wilson loop in $\mathcal{N}$=4 SYM theory provides an interesting example of renormalization group flow on a line defect: the scalar coupling parameter $\zeta$ has a non-trivial beta function and may be viewed as a running coupling constant in a 1d defect QFT. We continue the study of this operator, generalizing previous results for the beta function and Wilson loop expectation value to the case of an arbitrary representation of the gauge group and away from the planar limit. Focusing on the scalar ladder limit where the generalized Wilson loop reduces to a purely scalar line operator in a free adjoint theory, and specializing to the case of the rank $k$ symmetric representation of $SU(N)$, we also study a certain "semiclassical" limit where $k$ is taken to infinity with $k \zeta^2$ fixed. This limit can be conveniently studied using a 1d defect QFT representation in terms of path integral over $N$ commuting 1d bosons. Using this representation, we compute the beta function and circular loop expectation value in the large $k$ limit, and use it to derive constraints on the structure of the beta function for general representation. We discuss the corresponding 1d RG flow and comment on the consistency of the results with the 1d defect version of the F-theorem. ----------- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.

We will discuss generalized circular Wilson loops and 1d CFT defined by correlators of operators inserted along the loop following arXiv:1706.00756 and some more recent work.

Motivated by a desire to find a useful 2d Lorentz-invariant reformulation of the AdS_5 x S 5 superstring world-sheet theory in terms of physical degrees of freedom we construct a Pohlmeyer-reduced version of the corresponding sigma model. Starting with a coset space string sigma model in the conformal gauge and writing the classical equations in terms of currents one can fix the residual conformal diffeomorphism symmetry and kappa-symmetry and introduce a new set of variables (related locally to currents but non-locally to the original string coordinate fields) so that the Virasoro constraints are automatically satisfied. The resulting gauge-fixed equations can be obtained from a Lagrangian of a non-abelian Toda type: a gauged WZW-model with an integrable potential coupled also to a set of 2d fermionic fields. We show that in the special case of the AdS_2 x S2 superstring model the reduced theory is equivalent to the N=2 supersymmetric extension of the sine-Gordon model.