Talks

The study of symmetries at null infinity and their connection with soft theorems via Ward identities has been the subject of intense research over the past decade. The organization of the symmetries in a clear - geometric - structure that reflects the subleading infrared effects has led to numerous interesting results, in particular the emergence of the Lw_{1+\infty} algebra of symmetries for gravity. In this talk I will review recent results on an adaptation of Stueckelberg's procedure to extend phase spaces at null infinity, by which gauge symmetry generators are promoted to dynamical degrees of freedom, containing the so-called edge modes. This formalization allows us to obtain charges corresponding to the subleading soft theorems at all orders, and to construct a hierarchy of closed subalgebras that satisfy simple recursion relations. I will show the example of this construction in Yang-Mills theory, and comment on the charge algebra obtained. Finally, I will discuss the application of this construction to gravity, as well as some preliminary results and future directions.

Non-local operators, supported on submanifolds of spacetime, often encode fascinating physical insights about a theory and can serve as order parameters for phase transitions. In this talk, we will explore various aspects of 1/2​ BPS surface operators in N=4 super Yang-Mills. Specifically, I will show how supergravity computes exactly the planar limit of certain correlation functions of surface operators, even though they receive nontrivial quantum corrections. In particular, we will compute correlation functions with Chiral Primary Operators by localizing N = 4 super Yang-Mills on S^4 to a deformed version of 2d Yang-Mills on S^2. These correlation functions, which have a finite number of quantum corrections, can also be computed perturbatively in four dimensions. I will show the exact agreement between these approaches and the corresponding supergravity result. This talk is based on 2406.08541, work in collaboration with Changha Choi and Jaume Gomis.

Directional dark matter detectors using diamond as a target material offer a novel solution to overcome solar neutrino backgrounds. Sub-micron damage tracks from nuclear recoils can be read out via advanced quantum sensing techniques with nitrogen-vacancy (NV) centers. I will discuss recent advancements in strain-sensitive quantum interferometry that enable precise strain imaging, paving the way for directional particle detection. These developments highlight the potential of diamond-based detectors for advancing dark matter and neutrino physics, as well as material science applications.

Emergent Modified Gravity (EMG) is a post-Einsteinian theory of canonical gravity. In this formulation, modified constraints are required to preserve an algebra of hypersurface deformation form and will in general imply modified structure functions. This procedure leads to the conclusion that spacetime is an emergent object with a nontrivial dependence on the gravitational phase space variables through the modified structure functions. Consistency conditions are imposed on the modified constraints and the emergent spacetime metric to ensure general covariance. The resulting modifications allowed by EMG go beyond those obtained from adding higher curvature terms and can result in nonpolynomial dependencies on extrinsic curvature components. In this talk, we discuss how a particular interpretation of such modifications as holonomy terms makes it possible to use EMG as a covariant framework for effective (loop) quantum gravity. We then focus on dynamical solutions of the spherically symmetric model which include nonsingular black holes, new effects to gravitational collapse, and MOND-like effects at intermediate scales.

The groundbreaking detection of gravitational waves from merging black holes has forever changed how we observe the Universe. Upcoming detectors, like the Laser Interferometer Space Antenna (LISA), will unlock new opportunities by allowing us to detect mergers between stellar-mass black holes (tens of solar masses) and supermassive black holes (SMBHs, millions to billions of solar masses). These fascinating events, known as extreme-mass-ratio inspirals (EMRIs), provide a wealth of information about the dynamics near SMBHs. A key formation channel for EMRIs involves weak gravitational interactions—two-body kicks—from surrounding stars and compact objects that gradually alter the small black hole's orbit, eventually driving it into the SMBH. However, the picture changes when we consider the presence of SMBH companions, which can induce high orbital eccentricities, further enhancing EMRI formation. In this talk, I will show that combining these two processes is crucial for understanding the progenitors of EMRIs. Moreover, I will demonstrate that SMBH binaries create EMRIs more efficiently than either process alone, making it truly rain black holes! This scenario results in a substantial stochastic gravitational wave background for future detectors like LISA. Finally, I will also discuss how this mechanism affects tidal disruption events and address the tantalizing question: Is it raining stars, too?

I'll discuss the representation theory of line operators in 3d holomorphic-topological theories, following recent work with Wenjun Niu and Victor Py. Examples of the line operators we have in mind include half-BPS lines in 3d N=2 supersymmetric theories (reinterpreted in a holomorphic twist). We compute the OPE of line operators, which endows the category with a meromorphic tensor product, and establish a perturbative nonrenormalization theorem for the OPE. Then, applying Koszul-duality methods of Costello and Costello-Paquette, we represent the category of lines as modules for a new sort of mathematical object, which we call a dg-shifted Yangian. This is an A-infinity algebra, with a chiral coproduct whose data includes a Maurer-Cartan element that behaves like an infinitesimal r-matrix. The structure is a cohomologically shifted version of the ordinary Yangians that represent lines in 4d holomorphic-topological theories.