Week 12.10.2026 – 18.10.2026

We will discuss how to bootstrap string theory in AdS, using N=4 SYM as a concrete example. The first lecture will review the basic ingredients of AdS/CFT: the definitions of AdS and CFT, the correspondence between Kaluza–Klein modes and single-trace operators, and the relation between string scattering in AdS and correlation functions of Kaluza–Klein modes in the CFT. The second lecture will focus on the stress-tensor multiplet four-point function, including its conformal block expansion, the constraints imposed by superconformal Ward identities, and its formulation in Mellin space. The third lecture will introduce the flat-space limit, explain how it acts on the conformal block expansion, and discuss the spectrum of single-trace operators that survives at strong coupling. In the final lecture, we will go beyond the flat-space limit and study the first AdS correction. We will introduce a worldsheet ansatz for this correction and show how matching it to the conformal block expansion fixes the correction completely.

Please register here: https://forms.gle/7zfqxHjCDSdDesmy7

The recent discovery of a known infinite-dimensional algebra, w(1+infinity), among the asymptotic symmetries of four-dimensional asymptotically flat spacetimes has been interpreted as key evidence in support of a bottom-up approach to flat-space (a.k.a. celestial) holography.  In particular, since a holographic theory must realize the symmetries of its associated gravitational dual, large universal symmetries in principle impose fairly stringent constraints on a holographic correspondence. Of course, concrete progress relies crucially on the precise strength of the constraints from symmetry. Thus in pursuit of this larger goal, in this seminar, I will present a precise avatar of the universal  w(1+infinity) symmetry algebra that persists in the absence of gravity and in particular is realized in generic interacting four-dimensional conformal field theories.  The generators of the algebra are light-ray operators formed from null integrals of the stress tensor that generalize the average null energy operator.  I will discuss potential implications for conformal field theories in spacetime dimensions greater than two and celestial holography.

Please register here: https://forms.gle/7zfqxHjCDSdDesmy7

I will address the question: In what situations are perturbative quantum gravity effects important at distances much longer than the Planck scale? Among other examples, I will calculate the `quantum width' of the black hole horizon.