Talks

Quantum entanglement measures of many-body states have been increasingly useful to characterize phases of matter. Here we explore the surprising connection between symmetry-protected topology (SPT) and separability of their boundary mixed states. More specifically, we consider lattice systems in d space dimensions with anomalous symmetry G, where the anomaly is characterized by a bulk SPT invariant in the group cohomology Hd+2(G,U(1)). We show that any mixed state ρ that is strongly symmetric under G, in the sense that G ρ ∝ ρ, is necessarily (d+2)-nonseparable, i.e. is not the mixture of tensor products of d+2 states in the Hilbert space. Furthermore, such states cannot be prepared from any (d+2)-separable states using finite-depth local quantum channels, so the non-separability is long-ranged in nature. The anomaly-nonseparability connection also allows us to generate simple examples of mixed states with nontrivial multi-partite entanglement.

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In this talk I will discuss the rich interplay of light particles with density. In particular, I will show that the couplings of the QCD axion get modified in high density conditions. I will discuss the implications on astrophysical constraints, such as supernova and neutron star bounds. I will then look at the impact that axion-like particles can have on the structure of neutron stars

We tackle the question of whether regular black holes or other alternatives to the Schwarzschild solution can arise from an action principle in quantum gravity. Focusing on an asymptotic expansion of such solutions and inspecting the corresponding field equations, we demonstrate that their realization within a principle of stationary action would require either fine-tuning, or strong infrared non-localities in the gravitational effective action. We will also show that the black hole entropy of theories displaying such infrared non-localities diverge. The principle of least action and the consistency of Wald entropy thus yield non-trivial asymptotic constraints on the metric of quantum black holes.

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To set the stage, I discuss different assumptions about physics beyond GR and resulting expectations about where to look for the breakdown of the Kerr paradigm. In particular, I present counterexamples to the prevailing expectation that deviations from GR are necessarily tied to local curvature scales. This provides a motivation to probe for a potential breakdown of black-hole uniqueness, not just for solar-mass but also for supermassive black holes. I will then focus on how to leverage VLBI observations of light emitted in the accretion disk to probe the stationary and axisymmetric background spacetime. I will detail different assumptions about additional hidden symmetries of the spacetime and how to then systematically parameterize deviations. Within such a parametrization, I will demonstrate a systematic lensing-band framework to exclude spacetimes for which an observed VLBI feature cannot arise from geodesics that traversed the equatorial plane more than once. If time permits, I will also address complimentary tests with solar-mass binaries and possible pathways to achieve stable nonlinear evolution.

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The Levin-Wen model is known to produce a vast array of topological phases of matter. Among these theories are gauge theories such as the twisted quantum double. In this talk, we will show that the Levin-Wen model is itself a gauge theory. In particular, given a unitary fusion category C, we construct a globally tube algebra (Tube(C)) symmetric lattice model and gauge this symmetry to produce the Levin-Wen model with anyons described by the Drinfeld center Z(C). This construction endows the terms of the Levin-Wen Hamiltonian with the interpretation of flux and charge operators for the Tube(C) gauge symmetry. Furthermore, this construction gives a gauge theoretic interpretation to the mathematical fact that the category of representations of Tube(C) is equivalent to Z(C). To demonstrate this new class of Tube(C) symmetric theories, we will explicitly explore the case where C is the Fibonacci category Fib. We will write down the ungauged Tube(Fib) symmetric theory, compute the symmetry action, and show how to gauge the Tube(Fib) global symmetry to produce the double Fibonacci Levin-Wen model.

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