Quantum Gravity and Entanglement in Particle Physics and Gravitation

Some approaches to Quantum Gravity (QG) entail decoherence of quantum matter propagating in it, due to an “environment” of QG degrees of freedom inaccessible to lowenergy observers. In the first part of this talk, I discuss potential, and rather unique, effects of QG-induced decoherence on entangled particle states, specifically an induced modification of Einstein-Podolsky-Rosen (EPR) correlations of entangled neutral-meson states in meson factories (ω-effect). In the second part, I summarise a recent work in which axion-like fields, forming a kind of condensate clouds surrounding rotating (Kerrtype) astrophysical black holes, can lead to superradiant instabilities, and, through these, to the production of EPR-like entangled states of gravitons, with the entanglement pertaining to (left, right) polarisation degrees of freedom. In the presence of axions and Kerr geometries, there are non-trivial gravitational Chern-Simons (gCS)-type anomalous terms in the respective low-energy gravitational effective actions. Depending on whether the graviton entanglement is due to the non-anomalous terms (of General-Relativity type) in the effective action, or to the gCS terms, one obtains different structures of the resulting entangled squeezed-graviton states, which resemble somewhat the ω-effect.