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MP: Fachverband Theoretische und Mathematische Grundlagen der Physik

MP 2: Quantum Field Theory I

MP 2.3: Talk

Monday, March 20, 2023, 17:20–17:40, ZEU/0250

Information theoretic properties of soft photon clouds — •Henning Bostelmann¹, Daniela Cadamuro², and Wojciech Dybalski³ — ¹Department of Mathematics, University of York, UK — ²Institute for Theoretical Physics, University of Leipzig, Germany — ³Adam Mickiewicz University, Poznań, Poland

In quantum field theories with massless particles, states which describe clouds of soft photons in front of the vacuum are macroscopically different from the vacuum state: in mathematical terms, they lead to inequivalent representations of the quasilocal observable algebra, and a global ``photon charge'' labels these representations.

Here we investigate this macroscopic difference from an information-theoretic perspective. In a massless free theory, we compute the relative entropy between a coherent photon cloud state and the vacuum with respect to the forward lightcone algebra. It turns out that this entropy is infinite if, and only if, the ``photon charge'' of the cloud is zero.