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: The structure of the initial conditions of the universe

Abstract: I will review what we know about the initial conditions of the universe from observations. Then, I will explain how they arise within the framework of inflation, and describe recent progress in classifying (or “bootstrapping”) the possible correlation functions between primordial fluctuations. Finally, time permitting, I will touch upon work in progress trying to apply the bootstrap philosophy to more general cosmologies.

Title: Holography of Chronology Protection

Abstract: After an introduction to time-machine spacetimes and simple models of them, I will discuss recent work with M. Tomasevic where we use holography to study quantum effects when closed timelike curves (CTCs) are developed. We address the question of whether it is possible to send a signal across the chronology horizon, passing into the region where CTCs are present. We find that the self-interaction of quantum fields manages to banish the passage of field excitations into the non-chronal region. Going further, we compute the gravitational backreaction of the quantum fields, and show that the null chronology horizon turns into a strong, spacelike curvature singularity. This is one of the few controlled, explicit examples where we can see quantum effects change a Cauchy horizon into a spacelike singularity.

Title: Mastering bounds on correlators

Abstract: We discuss a new viewpoint onto the CFT landscape: bounds on values of CFT correlators. We show that such bounds can be obtained by constructing suitable ‘master functionals’. We present both numerical results for 3d CFTs as well as exact results for correlators on the line. The latter follow from crossing symmetric dispersion relations. We briefly discuss how these may be used to study the Regge and flat space limits of CFT correlators.

**Title: **Multi-trace correlators in the SYK model and Non-geometric wormholes

**Abstract: **We consider the global fluctuations in the density of states of the SYK model, which are much larger than the standard RMT correlations. We provide a diagrammatic description of their leading and subleading behavior. In either case, the new set of correlations are not associated with (and are much larger than) the ones given by topological wormholes, and hint towards the dual of a single realization. In particular, we suggest that incorporating them in the gravity description requires the introduction of new, lighter and lighter, fields in the bulk with fluctuating boundary couplings.

* Title: *Bootstrapping

*N*= 4 super-Yang-Mills on the conformal manifold

** Abstract: **We study the

*N*= 4 SYM stress tensor multiplet 4-point function for any value of the complexified coupling tau, and in principle any gauge group (we focus on SU(2) and SU(3) for simplicity). By combining non-perturbative constraints from the numerical bootstrap with two exact constraints from supersymmetric localization, we are able to compute upper bounds on low-lying CFT data (e.g. the Konishi) for any value of tau. These upper bounds are very close to the 4-loop weak coupling predictions in the appropriate regime. We also give preliminary evidence that these upper bounds become small islands under reasonable assumptions, in which case our method would provide a numerical solution to

*N*= 4 SYM for any gauge group and tau.

**Title: **Thermal Order in 3d

**Abstract: **Our intuitive understanding of thermodynamics suggests that broken global symmetries in the stable vacuum of a physical system, get restored at high temperatures. We construct a unitary, UV-complete 3d QFT that instead exhibits a spontaneous breaking of continuous symmetries at all temperatures. Our model consists of two copies of the long-range vector model, with O(m) and O(N−m) global symmetry groups, perturbed by double-trace deformations. The model exhibits a conformal manifold in the large rank limit, that is lifted by 1/N corrections. A certain class of IR fixed points are shown to undergo SSB at finite temperature, with the pattern persisting to all temperatures due to scale-invariance. We provide evidence that the models in question are unitary, UV-complete, as well as invariant under conformal symmetry. Our work adds to the growing list of models that display persistent symmetry breaking (PSB), and discusses the necessary conditions for the models to display such a behaviour.

**Title: **Conformal operators in SYK-like models and their numerical effects

**Abstract: **Quantum mechanical models with random interactions have an infinite number of bilinear operators, the scaling dimensions of which can be computed explicitly in the large N limit. The lowest dimension operators play an important role in thermodynamical properties of these models and define the behavior of various correlation functions in the infrared limit. In this talk I’ll show that some SYK-like models have operators with unusual anomalous dimensions. I also demonstrate how they can be observed in numerical computations.

Based on works with Maria Tikhanovskaya, Haoyu Guo and Subir Sachdev

https://arxiv.org/abs/2010.09742

https://arxiv.org/abs/2012.14449

**Title:** Magnetic Quivers, Phase Diagrams, and Physics at Strongly Coupled Quantum Field Theories

**Abstract:** Quiver gauge theories experienced a breakthrough in activity through two important concepts, called “magnetic quivers” and “Hasse (phase) diagrams”. The first helps understanding the physics of strongly coupled gauge theories and exotic theories with tensionless strings in 6d or with massless gauge instants in 5d. The second gives an invaluable information about the phase structure of gauge theories, in analogy with phases of water. The talk will review these developments and explain their significance.

** Title: **Some aspects of line defects in d dimensions

** Abstract:** We consider renormalization group flows on line defects in d dimensions. We define a “defect entropy” and argue that it decreases monotonically during RG flows. We apply this result to line defects which appear in condensed matter and high energy physics, including magnetic (SPT) defects, localized field defects, and Wilson loops. In some of these cases we make some new experimental predictions and in the case of Wilson lines we make some comparisons with localization and holography.

**Title: **Automorphic Spectra and the Conformal Bootstrap

**Abstract: **I will explain that the spectral geometry of hyperbolic manifolds provides a remarkably faithful model of the modern conformal bootstrap. In particular, to each hyperbolic manifold, one can associate a Hilbert space of local operators, which is a unitary representation of a conformal group. The scaling dimensions of the operators are related to the eigenvalues of the Laplacian on the manifold. The operators satisfy an operator product expansion. Finally, one can define their correlation functions and derive bootstrap equations constraining the spectrum. As an application, I will use conformal bootstrap techniques to derive upper bounds on the lowest positive eigenvalue of the Laplacian on closed hyperbolic surfaces and 2-orbifolds. In a number of notable cases, the bounds are nearly saturated by known surfaces and orbifolds. For instance, the bound on all genus-2 surfaces is λ1≤3.8388976481, while the Bolza surface has λ1≈3.838887258. The talk will be based on https://arxiv.org/abs/2111.12716, which is joint work with P. Kravchuk and S. Pal.