Triangle Seminars

Abstract:
Electromagnetism links phenomena across all scales, from atomic structure and chemistry to the physics through which we access the distant universe. In this talk, I will describe my own journey toward understanding the photon. We will try to understand what makes photons robustly massless, and see how they can arise from condensed strings or emerge in simple spin systems, including ones with little to no symmetry. Finally, we will speculate on possible UV completions of electromagnetic theories, and ask whether life could even exist in a universe without light.

Abstract:
Postponed!

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TBA

Abstract:
We present a semiclassical framework for computing the scaling dimensions of heavy neutral composite operators in conformal field theories (CFTs), providing a controlled and intuitive approach that extends beyond standard perturbative and numerical methods. Using the state–operator correspondence, the problem is mapped to the semiclassical quantization of periodic, spatially homogeneous classical field configurations on the cylinder. The Wilson–Fisher fixed point of the ϕ4 theory serves as a primary case study, and we conclude with brief remarks on extensions to other CFTs. The talk is based on: 2408.01414 [hep-th], 2511.08276 [hep-th], 2512.23539 [hep-th].

Abstract:
The existence of an event horizon is the defining property of a black hole. I shall review the properties of event horizons and discuss various examples demonstrating that event horizons are not smooth in dynamical processes such as black hole formation or merger. I shall explain how non-smooth features of an event horizon can be classified into various types, such as creases and caustics. I shall classify "perestroikas" of these structures, in which they undergo a qualitative change at an instant of time. A crease perestroika gives an exact local description of the event horizon near the "instant of merger" of a black hole merger. Other crease perestroikas describe event horizon nucleation or collapse of a hole in a toroidal horizon. Caustic perestroikas provide a mechanism for smoothing the horizon.

Abstract:
The KLT double copy relates open string amplitudes to closed string amplitudes, which provides the string-theoretic version of the more familiar relation Gravity=(Yang-Mills)^2. This relation is mediated by the KLT Kernel. In field theory, this kernel is well-studied, and it is the inverse of a matrix of amplitudes in bi-adjoint scalar theory (BAS). These amplitudes have been central in many recent advances in the field of scattering amplitudes. Crucially, it is known that these amplitudes have a completely geometric description in terms of the ABHY associahedron.

By contrast, much less is known about the string theory KLT kernel. Its inverse defines some α'-completion of BAS amplitudes, and exhibits intrinsically stringy properties. In this talk, I will show that these 'stringy BAS' amplitudes also admit a description from positive geometry. We will see how the stringy features emerge from this geometric description. Furthermore, I will argue that this geometry also contains all pion amplitudes in the Non-Linear Sigma Model, as well as mixed pion/BAS amplitudes. This gives us a first glimpse into how the positive geometry framework can be used to capture truly stringy features, and can be extended beyond the realm of rational functions.

Based on: Phys.Rev.Lett. 136 (2026) 1, 011601 (https://journals.aps.org/prl/abstract/10.1103/lb5l-twsb), Arxiv: 2508.20161 (https://arxiv.org/abs/2508.20161)

Abstract:
Quantum London Seminar (LIMS+QMUL joint seminar)

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This talk will present the systematic exploration of quantum phases of matter with generalized (categorical) symmetries, by means of the "Symmetry Topological Field Theory" (SymTFT). After introducing the general framework, I will discuss novel examples, including intrinsically gapless phases (which cannot be deformed to gapped phases with analogous symmetry properties) and gapped phases in which the symmetry broken vacua carry distinct kinds of topological order. I will also illustrate how ideas and techniques from the SymTFT can be used to obtain new results in quantum information.

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For more info, please find https://lims.ac.uk/

Abstract:
TBA