High Energy Physics

We argue that generic local subregions in semiclassical quantum gravity are associated with von Neumann algebras of type II_1, extending recent work by Chandrasekaran et.al. beyond subregions bounded by Killing horizons. The subregion algebra arises as a crossed product of the type III_1 algebra of quantum fields in the subregion by the flow generated by a gravitational constraint operator. We conjecture that this flow agrees with the vacuum modular flow sufficiently well to conclude that the resulting algebra is type II_\infty, which projects to a type II_1 algebra after imposing a positive energy condition. The entropy of semiclassical states on this algebra can be computed and shown to agree with the generalized entropy by appealing to a first law of local subregions. The existence of a maximal entropy state for the type II_1 algebra is further shown to imply a version of Jacobson’s entanglement equilibrium hypothesis. We discuss other applications of this construction to quantum gravity and holography, including the quantum extremal surface prescription and the quantum focusing conjecture.

In holography, the quantum extremal surface formula relates the entropy of a boundary state to the sum of two terms: the area term and the entropy of bulk fields inside the entanglement wedge. As the bulk effective field theory suffers from UV divergences, the second term must be regularized. It has been conjectured since the work of Susskind and Uglum that the renormalization of Newton’s constant in the area term exactly cancels the difference between different choices of regularization for bulk entropy. In this talk, I will explain how the recent developments on von Neumann algebras appearing in the large N limit of holography allow to prove this claim within the framework of holographic quantum error correction, and to reinterpret it as an instance of the ER=EPR paradigm. This talk is based on the paper arXiv:2302.01938.

While entanglement has been examined extensively in AdS/CFT, it has avoided significant attention in the study of celestial holography and asymptotic symmetries relevant to asymptotically flat spacetime. I will present work that considers the entanglement of a Milne patch for Maxwell theory in Minkowski spacetime from the perspective of celestial holography. In the Minkowski vacuum, we find that the Milne patch is thermally entangled. We interpret the thermal entangling operator that builds the Minkowski vacuum from the Milne vacuum as an interaction term in the celestial CFT. We further examine the edge modes of the Milne patch, assigning them a physical interpretation as fluctuations in Milne asymptotic charge. Interestingly, we find that the constraint governing these edge modes includes sources that avoid the Minkowski interior. Altogether, by studying entanglement along the extra holographic direction present in celestial holography but absent in AdS/CFT, our work bridges a critical gap between our understanding of entanglement in the latter and the physically relevant setting of asymptotically flat spacetime.

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The holographic duality between strongly coupled quantum field theories and weakly coupled gravitational theories in one higher dimension holds, in principle, the promise of understanding strongly coupled systems that occur in condensed matter physics, such as the "strange" metals that appear in materials such as high-Tc cuprates. Unfortunately, the holographic models of metals that have previously been studied have not been successful in capturing even the most basic physics that any realistic model of a metal should obey. In this talk, I will review the essential properties that any metal (strongly coupled or not) must satisfy, and propose a new holographic model that is consistent with these requirements. The new model is based on a radically different approach compared with previous holographic models of metals, and crucially relies on recent work that formulates in a precise way the conditions for an IR effective field theory to be "emergeable" from a UV theory at nonzero charge density. In particular, the holographic model I study is dual to a quantum field theory with a global symmetry group LU(1) -- the "loop group" whose elements are smooth functions from the circle into U(1). I present the results of a solution of the model and argue that its properties are qualitatively consistent with what one should expect to find in a strongly coupled metal.

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