# Departing members: Fiona Seibold (ETH Zurich, N. Beisert Group)

### 21 Jul 2020

Fiona successfully defended her PhD thesis entitled "*Integrable deformations of sigma models and superstrings"* on the 4th of May. She will be joining Arkady Tseytlin's group at Imperial College London in October, supported by an SNF early post-doc mobility grant "q-deforming AdS/CFT".

In her thesis, "*Integrable deformation of sigma models and superstrings*" she studied deformations of well-known integrable models (e.g. principal chiral model, symmetric space sigma model, AdS5xS5 superstring), focussing on so-called Yang-Baxter and lambda deformations. At the algebraic level, both correspond to q-deformations: the original symmetry algebra is promoted to a quantum group. A remarkable property of these deformations is that they preserve integrability: there exists a tower of conserved charges that constrain the theory so much that it can be solved exactly. However, if the original model is an integrable string theory, there is no guarantee that the deformed model will also be a string theory. In particular, no such Yang-Baxter deformations were known. One of the main result she obtained during her PhD was to show how to construct Yang-Baxter deformations that define string theories. This is an important step towards analysing these deformations in the context of the AdS/CFT correspondence.

Her SNF project aims at obtaining a q-deformed version of the AdS/CFT correspondence.