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: **String stars in anti de Sitter space**Abstract: **We study the ‘string star’ saddle, also known as the Horowitz-Polchinski solution, in the middle of d+1 dimensional thermal AdS space (d>2). We show that there’s a regime of temperatures in which the saddle is very similar to the flat space solution found by Horowitz and Polchinski. This saddle is hypothetically connected at lower temperatures to the small AdS black hole saddle. We also study, numerically and analytically, how the solutions are changed due to the AdS geometry for higher temperatures. Specifically, we describe how the solution joins with the thermal gas phase, and find the leading correction to the Hagedorn temperature due to the AdS curvature. Finally, we study the thermodynamic instabilities of the solution and argue for a Gregory-Laflamme-like instability whenever extra dimensions are present at the AdS curvature scale.

**Title: **Love and Naturalness

**Abstract: **It has been known for a decade that black holes are the most rigid objects in the universe: their tidal deformations (Love numbers) vanish identically in general relativity in four dimensions. This has represented a naturalness problem in the context of classical worldline effective field theory. In my talk I will present a new symmetry of general relativity (Love symmetry) that resolves this naturalness paradox. I will show that perturbations of rotating black holes enjoy an SL(2,R) symmetry in the suitable defined near zone approximation. This symmetry, while approximate in general, in fact yields exact results about static tidal deformations. This symmetry also implies that generic regular black hole perturbations form infinite-dimensional SL(2,R) representations, and in some special cases these are highest weight representations. It is the structure of these highest weight representations that forces the Love numbers to vanish. All other facts about Love numbers, including their puzzling behaviour for higher dimensional black holes, also acquire an elegant explanation in terms of SL(2,R) representation theory.

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**Title: **Fracton-Elasticity Duality and Dipole Gauge Symmetry**Abstract: **The generalization of particle-vortex duality in 2+1 dimensions to elasticity introduces emergent tensor gauge fields coupled to immobile charges, identified as fractons. We reformulate the duality in terms of ordinary gauge fields and derive mobility restrictions from gauge invariance.

**Title: **Large-Twist Limit for Any Charged Operator in N=4 SYM

**Abstract: **The fishnet theory was obtained as a strongly twisted, weakly coupled limit of N=4 SYM. Though still non-trivial, it is much simpler than the original N=4 SYM theory. The appearance of integrability is better understood (at least for the spectrum), and the holographic dual was constructed from first principles. Both can be tied to the existence of an iterative structure for some of the correlators. However, the fishnet theory only contains two scalar fields, and most of the operators of the original theory are now protected. In particular, the gauge boson has completely decoupled. We argue that it is possible to devise a double-scaling limit for any operator charged under the R-symmetry in N=4 SYM. We consider several examples that were protected in the fishnet theory, including operators containing the gauge boson. We show that the generic situation involves some type of mixing with other operators. This work is a first step towards a systematic expansion of N=4 SYM around the large-twist limit.

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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.