During the semester we have a high energy seminar and a lunch seminar. In addition to these two seminars we participate in a joint theoretical high energy theory seminar in Newe Shalom. The joint seminar takes place on Tuesdays from 10:30 until 13:30 and includes two talks and lunch. This seminar is attended by the high energy groups of all the Israeli institutions and usually attracts a crowd of roughly twenty participants.

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**Title**: Krylov complexity in quantum field theory and beyond**Abstract**: Krylov complexity, and dynamics in Krylov space more generally, have emerged recently as interesting probes of quantum dynamics. They were proposed as probes of quantum chaotic dynamics, relating the latter to growth of OTOC. We discuss Krylov dynamics in case of quantum field theory, and first notice that in the conformal case Krylov complexity behaves universality with no regard to integrability or chaos of the underlying theory. We then discuss turning on mass, placing the theory on a space of finite size and/or introducing a UV cutoff. We notice that each of these deformations is reflected in Lanczos coefficients and in the behavior of Krylov complexity. We conclude with a conjecture strengthening the Maldacena-Stanford-Shenker bound on OTOC, outlining the role of UV cutoff in the context of “universal operator growth hypothesis” and argue behavior of Krylov complexity is qualitatively different from computational and holographic complexities.

**Title**: A simple model, extracted using holography, of a domain wall between a confining and a de-confining phases and its velocity.**Abstract**: In the context of theories with a first order phase transition, we propose a general covariant description of coexisting phases separated by domain walls using an additional order parameter-like degree of freedom. In the case of a holographic dual to a confining and a de-confing phases, the re- sulting model extends hydrodynamics and has a simple formulation in terms of an action and a corresponding energy-momentum tensor. The proposed description leads to simple analytic profiles of domain walls, including the surface tension density, which agree nicely with holographic numerical solu- tions. We show that for such systems, the domain wall or bubble velocity can be expressed in a simple way in terms of a perfect fluid hydrodynamic formula, and thus in terms of the equation of state. We test the predictions for various holographic domain walls.

Title: Mixed anomalies and generalized symmetries from 3d superconformal indices

Abstract: Generalized symmetries and their mixed anomalies have proved to be useful in providing non-trivial constraints on the dynamics of QFTs. A natural question is whether these are related in any way to supersymmetric partition functions or indices, which have also been used extensively to study SQFTs. In this talk, we address this question in the context of 3d $mathcal{N} geq ≥3$ gauge theories using the superconformal index. In particular, using the index we are able to detect mixed anomalies involving discrete 0-form symmetries, and possibly a 1-form symmetry. Gauging appropriate symmetries involved in such mixed anomalies, we obtain various interesting theories with two-group structures or non-invertible symmetries.

**Title**: Entanglement, Chaos and Quantum Computation

**Abstract**: We consider information spreading measures in randomly initialized variational quantum circuits and introduce entanglement diagnostics for efficient computation. We study the correlation between quantum chaos diagnostics, the circuit expressibility and the optimization of the control parameters.

**Title**: Thermalization and Chaos in 1+1d QFTs

**Abstract**: Nonintegrable QFTs are expected to thermalize and exhibit emergence of hydrodynamics and chaos. In weakly coupled QFTs, kinetic theory captures local thermalization; such a versatile tool is absent away from the perturbative regime. I will present analytical and numerical results using nonperturbative methods to study thermalization at strong coupling. I will show how requiring causality in the thermal state leads to strong analytic constraints on the thermodynamics and out-of-equilibrium properties of any relativistic 1+1d QFT. I will then discuss Lightcone Conformal Truncation (LCT) as a powerful numerical tool to study thermalization of QFTs. Applied to phi^{}^4 theory in 1+1d, LCT reveals eigenstate thermalization and onset of random matrix universality at any nonzero coupling. Finally, I will discuss prospects for observing the emergence of hydrodynamics in QFTs using Hamiltonian truncation.

**Title**: Holographic thermal correlators from supersymmetric instantons.

**Abstract**: I will present an exact formula for the thermal scalar two-point function in four-dimensional holographic conformal field theories. The problem of finding it reduces to the analysis of the wave equation on the AdS-Schwarzschild background. The two-point function is computed from the connection coefficients of the Heun equation, which can be expressed in terms of the Nekrasov-Shatashvili partition function of an SU(2) supersymmetric gauge theory with four fundamental hypermultiplets. At large spin the instanton expansion of the thermal two-point function directly maps to the light-cone bootstrap analysis of the heavy-light four-point function. Using this connection, we obtain the OPE data of heavy-light double-twist operators directly from the Nekrasov-Shatashvili function.

**Title**: Quantization of the Zigzag Model

**Abstract**: The zigzag model is a relativistic integrable N-body system describing the leading high-energy semiclassical dynamics on the worldsheet of long confining strings in massive adjoint two-dimensional QCD. I will discuss quantization of this model. I will demonstrate that to achieve a consistent quantization of the model it is necessary to account for the non-trivial geometry of phase space. The resulting Poincaré invariant integrable quantum theory is a close cousin of TT¯ deformed models.

__Title__: Classical Physics from Scattering Amplitudes

__Abstract__:

Recent years have seen great progress in our understanding of the emergence of classical physics from quantum scattering amplitudes, in both gauge and gravitational theories. This program is motivated by several reasons. One of them is the idea that amplitudes manifest certain physical properties that are not apparent otherwise. As an example of this idea, I will show how the double copy property of scattering amplitudes constrains the structure of the worldline EFT.

**Title**: Field theory defects through double scaling limits

**Abstract**: Defect operators in field theory are very interesting for a number of reasons. Drawing inspiration from techniques which have been very recently applied to uncover interesting properties of sectors of operators with large charge under a global symmetry, we will study defects in the Wilson-Fisher fixed point near d=4,6 dimensions. Combining with localization, we will also use a double-scaling limit for certain Wilson loops in N=2 supersymmetric theories in 4d which allows to make exact statements at finite N.

**Title**: Bounds on Regge growth of flat space scattering from bounds on chaos

**Abstract**: We will explain a study of four-point functions of scalars, conserved currents, and stress tensors in a conformal field theory, generated by a local contact term in the dual bulk description, in two different causal configurations. The first is the standard Regge configuration in which the chaos bound applies. The second is the ‘causally scattering configuration’ in which the correlator develops a bulk point singularity. We find an expression for the coefficient of the bulk point singularity in terms of the bulk S matrix of the dual bulk metric, gauge fields, and scalars, and use it to determine the Regge scaling of the correlator on the causally scattering sheet in terms of the Regge growth of this S matrix. We then demonstrate that the Regge scaling on this sheet is governed by the same power as in the standard Regge configuration, and so is constrained by the chaos bound, which turns out to be violated unless the bulk flat space S matrix grows no faster than $s^2$ in the Regge limit. It follows that in the context of the AdS/CFT correspondence, the chaos bound applied to the boundary field theory implies that the S matrices of the dual bulk scalars, gauge fields, and gravitons obey the Classical Regge Growth (CRG) conjecture. We will also comment on recent progress in the same direction.