Mathematical physics

Can gravity, in certain regards, be the `product' of two gauge theories, such as those appearing in the Standard Model? I will begin by reviewing the Bern—Carrasco—Johansson colour—kinematics duality conjecture, which implies that one can write the scattering amplitudes of Einstein-Hilbert gravity (coupled to a Kalb-Ramond 2-form and dilaton scalar) as the double copy of Yang—Mills amplitudes. Although the colour—kinematics duality, and therefore the double copy, was quickly established at the tree level, it remains a longstanding open problem at the loop level, despite highly non-trivial explicit examples. I will then describe how one can take this `gravity = gauge x gauge' amplitude paradigm `off-shell’ as a product of spacetime fields: the Yang-Mills BRST-Lagrangian itself double copies into perturbatively quantised Einstein-Hilbert gravity coupled to a Kalb-Ramond 2-form and dilaton, establishing the validity of the double copy to all orders, tree and loop. I will end by briefly discussing the homotopy algebras underpinning this result and the inclusion of supersymmetry, which reveals fascinating octonionic structures (some very well-known, others completely new) that will be the subject of Mia Hughes's talk in the following week.

"Non-equilibrium statistical mechanics has seen some impressive developments in the last three decades, thank to the pioneering works of Evans, Cohen, Morris and Searles on the violation of the second law, soon followed by the ground-breaking formulation of the Fluctuation Theorem by Gallavotti and Cohen for entropy fluctuation in the early nineties. Their work was by vast literature, both theoretical and experimental The extension of these results to the quantum setting has turned out to be surprisingly challenging and it is still an undergoing effort. Kurchan’s seminal work (2000) showed the measurement role has to be taken in account, leading to the introduction of the so called two-time measurement statistics (also known as full counting statistics). However in this context, the lack of a trajectory notion leads to both conceptual and technical problems, or phenomena with no classical counterpart, as underlined by some of our recent results. In this talk I will review some of the key concept involved in the Fluctuation Theorem and its extensions to the quantum setting; I will present some recent results exploring the role played by ultraviolet regularity conditions (joint work with R.Raquépas and T.Benoist )."

"I discuss applications of a hidden $U_q(\mathfrak{sl}_2)$-symmetry in CFT with central charge $c \leq 1$ (focusing on the generic, semisimple case, with $c$ irrational). This symmetry provides a systematic method for solving Belavin-Polyakov-Zamolodchikov PDE systems, and in particular for explicit calculation of the asymptotics and monodromy properties of the solutions. Using a quantum Schur-Weyl duality, one can understand solution spaces of such PDE systems in a detailed way. The solutions, in turn, are useful both for CFT questions and for rigorous understanding of the connections of 2D CFT with critical models of statistical physics."

The Boltzmann--Gibbs entropy is a functional on the space of probability measures. One characterization of the Boltzmann--Gibbs entropy is given by the Shannon--Khinchin axioms, which consist of continuity, maximality, expandability and extensivity. The extensivity is expressed in terms of the linear combinations of conditional probabilities. Replacing the coefficients in the linear combinations with a power function provides a characterization of the Tsallis entropy. I talk about the impossibility to replace the coefficients with a non-power function.

" In this talk, I posit two concepts from the economics literature as hypotheses for the observed data on women in academia. This talk includes time for discussion about how these concepts can inform our approach to mentoring junior women. "

"Geometrically, a gauge theory consists of a spinor bundle describing the matter fields, associated to some principal bundle whose gauge group rules the internal symmetries of the system. The gauge fields are the local expressions of a principal connection inducing a covariant derivative which settles the dynamics of the matter fields. Principal connections can be seen as parallel displacements on the fibres of the principal bundle along curves on the base manifold. In this talk I shortly present a generalisation of gauge fields given by direct connections on gauge groupoids, based on a work in progress with S. Azzali, Y. Boutaib, A. Garmendia and S. Paycha."

In this talk we will introduce categories, a notion that packages mathematical objects of any kind and provides an abstract language to study them. We will build up our way towards so-called modular tensor categories, which roughly speaking are categories with a tensor product, duals, and quite a bit of extra categorical structure. They arise in (rational) conformal field theory and its study poses many interesting questions on their classification, internal structure and generalizations. I will give an overview of these questions and some current lines of research in this topic.

The physics of General Relativity is deeply intertwined with the mathematics of Lorentzian differentiable manifolds. The latter provide excellent models of spacetime across a vast range of physical scales, encoding gravitational interactions into the curvature properties of smooth metric spaces. However, describing geometry in terms of the infinitesimal line element "ds" does not seem appropriate in the quantum regime near the Planck scale. -- Coming from different perspectives, geometers, classical relativists and quantum gravity researchers are actively investigating more general geometric settings, abandoning smoothness or even continuity of the metric space. The crucial question is what aspects of standard (pseudo-)Riemannian geometry survive, and what this tells us about the "essence" of curvature and geometry and about the ultimate nature of physical spacetime. Can we learn from each others' insights?

In this talk we will introduce generalized hyperpolygons, which arise as Nakajima-type representations of a comet-shaped quiver, following recent work joint with Steven Rayan. After showing how to identify these representations with pairs of polygons, we shall associate to the data an explicit meromorphic Higgs bundle on a genus-g Riemann surface, where g is the number of loops in the comet. We shall see that, under certain assumptions on flag types, the moduli space of generalized hyperpolygons admits the structure of a completely integrable Hamiltonian system.

I will discuss some of the mathematical puzzles that arise from the causal set approach to quantum gravity. In this approach, any causal continuum spacetime is said to be emergent from an underlying ensemble of locally finite posets which represents a discretisation of the causal structure. If the discrete substructure is to capture continuum geometry to sufficient accuracy, then it must be "approximately" close to it. How can we quantify this closeness? This discreteness, while also preserving local Lorentz invariance, leads to a fundamental non-locality. This is not only an obstacle to a “traditional” initial value formulation, but also to the geometric interpretation of entanglement entropy. Is there an analytic way to quantify the remanent Planckian non-locality? These questions, as well as others arising from the quantum dynamics of causal, may be of potential interest to mathematicians, in particular Geometers and Combinatorists.