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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` ` Sun Mon Tue Wed Thu Fri Sat Rob Myers, Perimeter Institute 4:00 pm Rob Myers, Perimeter Institute Apr 26 @ 4:00 pm – 6:00 pm Title: Complexity=Anything?Abstract: Motivated by holographic complexity, we examine a new class of gravitational observables in asymptotically AdS space associated with codimension-one slices or with codimension-zero regions. We argue that any of these observables is an equally viable …

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**Title: **Complexity=Anything?**Abstract: **Motivated by holographic complexity, we examine a new class of gravitational observables in asymptotically AdS space associated with codimension-one slices or with codimension-zero regions. We argue that any of these observables is an equally viable candidate as the extremal volume for a gravitational dual of complexity.

**Title: **Static Responses and Symmetries of Black Holes**Abstract: **__I will discuss features of the static responses of black holes in General Relativity. In particular, I will describe how black hole static responses are defined in point particle effective theory and will explain how the vanishing of black hole Love numbers is a consequence of symmetries of the wave equation in black hole backgrounds.__

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**Title: **Line Operators in Chern-Simons-Matter Theories and Bosonization in Three Dimensions**Abstract: **We study Chern-Simons theories at large N with either bosonic or fermionic matter in the fundamental representation. The most fundamental operators in these theories are mesonic line operators, the simplest example being Wilson lines ending on fundamentals. We classify the conformal line operators along an arbitrary smooth path as well as the spectrum of conformal dimensions and transverse spins of their boundary operators at finite ‘t Hooft coupling. These line operators are shown to satisfy first-order chiral evolution equations, in which a smooth variation of the path is given by a factorized product of two line operators. We argue that this equation together with the spectrum of boundary operators are sufficient to uniquely determine the expectation values of these operators. We demonstrate this by bootstrapping the two-point function of the displacement operator on a straight line. We show that the line operators in the theory of bosons and the theory of fermions satisfy the same evolution equation and have the same spectrum of boundary operators.

**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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