##### Meeting

#### Integrable effective field theories and their holographic descriptions

**Dec 16, 2019 - Dec 18, 2019**

**Abstract**

The recent discovery of exactly-solvable examples of effective field theories, such as the T-Tbar and J-Tbar perturbations of conformal field theories and their off-critical generalizations, have attracted the attention of theoretical physicists due to the many striking links with string theory and holography. The main aim of this meeting is to bring together theorists with complementary backgrounds on integrable models, string theory, AdS/CFT and entanglement to discuss features, applications and recent developments in two-dimensional quantum field theories deformed by irrelevant operators.

This meeting is partially supported by ETH Zurich through Career Seed Grant SEED-23 19-1.

**Organizers**

Domenico Orlando (INFN Torino), Alessandro Sfondrini (ETH Zurich), Roberto Tateo (Torino University)

**Contact**

sfondria@itp.phys.ethz.ch

**Talks**

Dec 16, 2019 - 09:45-10:30 | Roberto Tateo | TTbar-like deformations of some simple systems | Talk | Two-dimensional quantum field theory deformed by Zamolodchikov's TTbar operator has recently attracted the attention of theoretical physicists due to the many links with string theory and AdS/CFT. In this talk, I will review some interesting facts about the TTbar-like deformations of simple systems in one, two and four space-time dimensions. | ||||

Dec 16, 2019 - 11:00-11:45 | Riccardo Conti | Generalised irrelevant deformations of 2D integrable field theories | Talk | Among many interesting features, the TTbar deformation preserves the integrability of the original theory. In the first part of the talk, I will present an efficient method to explicitly compute the local conserved currents of a TTbar-deformed integrable field theory (IFT), using a field-dependent coordinate transformation involving the stress-energy tensor. In the second part, I consider an infinite family of coordinate transformations built out of generic conserved currents of the original IFT and I study the integrable structure of the corresponding deformed theories for a simple model. Quite remarkably, this analysis suggests that the finite-size spectrum of these perturbed systems is obtained by introducing Lorentz-breaking scattering phase factors in the S-matrix of the original theory. | ||||

Dec 16, 2019 - 12:00-12:45 | Andrew J. Tolley | TTbar, Massive Gravity and Non-critical Strings | Talk | I will argue that the natural gravitational picture of the TTbar deformation is ghost-free massive gravity, showing that massive gravity naturally emerges as an appropriately defined version of the random geometries framework. The important role of field dependent diffs is just a straightforward consequence of the Stuckelberg formalism of massive gravity. I will discuss these various connections, how (non)-critical strings arise naturally as the deformation of CFTs, and how to give path integral definitions for more general deformations. | ||||

Dec 16, 2019 - 13:00-14:30 | Lunch & discussion | Discussion | ||||||

Dec 16, 2019 - 14:30-15:15 | Alessandro Sfondrini | Generalised TTbar flow equations from scattering factorisation | Talk | Starting from the definition of the TTbar deformation as a CDD factor in the factorised S-matrix, I will show that one can derive generalised flow equations for two-dimensional Quantum Field Theories deformed by generalised current-current operators. I will also argue that a similar picture holds for integrable spin chains, where the CDD factor is taken as a deformation of the Bethe ansatz equations. This talk will be based on arXiv:1911.12233 and 1911.12315. | ||||

Dec 16, 2019 - 15:30-16:45 | Belazs Pozsgay | T-Tbar - deformation and long range spin chains | Talk | We show that the T-Tbar - deformation of integrable QFT has a natural counterpart in integrable spin chains: it corresponds to a certain kind of long range deformation which had already been studied in the literature. However, the connection between the two deformations was not yet noticed. We show that this connection can be understood through the current and generalized current operators. As a by-product we derive a rather general formula for the mean values of current operators in Bethe Ansatz solvable models. | ||||

Dec 16, 2019 - 16:45-19:00 | Free discussion | Discussion | ||||||

Dec 17, 2019 - 09:45-10:30 | Yunfeng Jiang | TTbar deformation on the lattice | Talk | Integrable quantum field theories (IQFT) can be regularized on the lattice while preserving integrability. The resulting lattice model is also integrable. We propose an integrable deformation of the lattice model such that in the continuum limit we obtain the TTbar deformed IQFT. | ||||

Dec 17, 2019 - 11:00-11:45 | Riccardo Borsato | Yang-Baxter and marginal deformations | Talk | I will review various aspects of Yang-Baxter deformations, keeping as a common theme their interpretation as marginal deformations. I will also remind how a subclass of Yang-Baxter (the TsT transformations) provide the holographic analog of the single-trace TTbar deformation, and of its generalisations. | ||||

Dec 17, 2019 - 12:00-12:45 | Thiago Rocha Araujo | Talk | ||||||

Dec 17, 2019 - 14:30-15:15 | Fiona Seibold | Reconciling integrable eta-deformations with supergravity | Talk | The study of integrable eta-deformations of AdS superstrings has led to a number of puzzles, in particular concerning the status of Weyl invariance in the deformed theories. In this talk, I will review the construction of the eta-models and discuss when the deformed backgrounds solve the standard type IIB supergravity equations of motion. While this resolves one of the main puzzles of eta-deformed superstrings, others remain including the behavior in the maximal deformation limit. | ||||

Dec 17, 2019 - 15:30-16:45 | Sibylle Driezen | Integrable $\lambda$-deformations | Talk | I will briefly review integrable $\lambda$-deformations of worldsheet models and their relation to T-dualities. I will discuss how the construction of the deformation can be generalised in various ways—while keeping (classical) integrability—focusing on recent work where the theory deforms an exact worldsheet CFT realised as an asymmetrically gauged Wess-Zumino-Witten model. As a low-dimensional example, I will apply this deformation to the Euclidean d = 2 ‘cigar’ black hole, corresponding to the axially gauged SL(2,R)/U(1) WZW theory, and I will argue the interest of this example as an integrable deformation of its Sine-Liouville holographic dual. | ||||

Dec 17, 2019 - 16:45-19:00 | Free discussion | Discussion | ||||||

Dec 18, 2019 - 09:45-10:30 | Kentaroh Yoshida | Talk | ||||||

Dec 18, 2019 - 11:00-11:45 | Yuta Sekiguchi | O(d,d) transformations preserve classical integrability | Talk | |||||

Dec 18, 2019 - 12:00-12:45 | Closing remarks (Orlando) | Talk | ||||||

Dec 18, 2019 - 14:30-19:00 | Free discussion | Discussion |