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.
Sun Mon Tue Wed Thu Fri Sat
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
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: Line defects in CFTs: from magnets to Wilson lines
Abstract: Line defects describe one-dimensional probes of a quantum field theory. Physically interesting examples can be found in different systems, ranging from condensed matter physics to gauge theories. In this talk, I will briefly review some recent results on the renormalization group approach to line defects in CFTs. I will then discuss some applications. In particular, I will discuss some interesting RG flows for Wilson lines in massless gauge theories, and their relation with an instability to screening by charged fields.
Title: Global symmetry breaking and defect conformal manifolds
Abstract:In the presence of exactly marginal operators, one can deform a conformal field theory to other such theories, forming a space of theories living on what’s known as the conformal manifold. In a theory with conformal defects, one may be able to retain the bulk theory but transform the defect along what I’ll call the “defect conformal manifold”. This requires the existence of exactly marginal defect operators. A simple setting where this happens is in the presence of a global symmetry broken by the defect. The broken symmetry current gives rise to an exactly marginal defect operator and a defect conformal manifold which is the symmetry breaking coset. This simple observation lets us derive an exact identity for integrated 4-point functions of the marginal defect operator which is highly nontrivial. We implement this in several models where the 4-point functions have been previously calculated.
Title: Effective theory of sub-maximal chaos
Abstract: I will present progress on formulating an effective description of the quantum butterfly effect at late times. After discussing maximally chaotic examples, I will turn to a particular limit of the SYK model that displays sub-maximal chaos and discuss its effective description. The final results can be matched in detail to stringy corrections to the gravitational eikonal S-matrix in holographic CFTs, including a stringy Regge trajectory, bulk to boundary propagators, and multi-string effects that are unexplored holographically.
Title: Chaos and Wormholes in the Sachdev-Ye-Kitaev Model
Abstract: The Sachdev-Ye-Kitaev (SYK) model is a solvable many-body theory with a low-energy limit given
by the Schwartzian action found for the boundary dynamics Jackiw-Teitelboim gravity. This model has greatly improved our understanding of many-body quantum chaos and black holes.
In this talk, after an introduction to the SYK model and random matrix theory, we discuss the physics of the spectral form factor as a measure of quantum chaos. We will see that the long time behavior of the spectral factor is closely related to wormhole solutions of two coupled SYK models.