Fri - 11/28/25

**Title:

      Quantum coherent dynamics of quasiclassical spacetimes**  - **Authors:** S. Wang, A. Sajeendran, D. Yeom, R. B. Mann, J. Foo  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  In a wide range of quantum gravity theories, quasiclassical geometries, which are solutions to the Einstein field equations approximately, are described by "coherent states." Here we propose a Hamiltonian formalism for gravitational dynamics with respect to this coherent state basis, which generates time evolution of the spacetime with respect to a clock at infinity. Since the coherent states are not orthogonal, an initial quasiclassical geometry is dynamically driven into a superposition of different amplitudes. Our framework provides a dynamical mechanism for tunneling between geometries that is ubiquitous in a number of approaches to quantum gravity, from loop quantum gravity to the Euclidean path integral. We apply our framework to the problem of black hole evaporation, providing a hint at how unitarity may be preserved with the inclusion of quantum corrections to the semiclassical evolution of the black hole.

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Thu - 11/27/25

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  1. [] - Title: On Modelling the Surfaces of Celestial Bodies in Quantum Gravity - Xavier Calmet, Marco Sebastianutti

Wed - 11/26/25

**Title:

      Krylov Complexity in Canonical Quantum Cosmology**  - **Authors:** Meysam Motaharfar, Maxwell R. Siebersma, Parampreet Singh  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We explore Krylov complexity for two exactly solvable models, one in the Wheeler-DeWitt (WDW) quantum cosmology and another in loop quantum cosmology (LQC), for a spatially flat, homogeneous, and isotropic universe sourced with a massless scalar field, which serves the role of clock. While the WDW quantization of this model cannot avoid the big bang/big crunch singularity, it is replaced by a big bounce in LQC. We construct the Krylov basis analytically by applying the Lanczos algorithm and evaluate both the Krylov state and operator complexity. In regimes where the wave function of the universe is sharply peaked, our results indicate that the Krylov complexity grows quadratically with the scalar field clock for the state and operator complexities in both the WDW quantum cosmology and LQC. We further show that operator complexity is exactly twice the state complexity in these regimes. We discuss the interpretation of the global behavior of these systems by calculating the Krylov entropy for both quantum cosmological frameworks. We observe that in LQC, the Krylov complexity and entropy remain finite at the bounce, whereas in the WDW quantum cosmology, they diverge at the big bang/crunch singularity. Our work paves the way for computing Krylov complexity in more intricate quantum cosmological models, including those exhibiting phenomena such as quantum chaos.

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Tue - 11/25/25

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Mon - 11/24/25

**Title:

      Finite-Dimensional ZX-Calculus for Loop Quantum Gravity**  - **Authors:** Ben Priestley  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  Loop quantum gravity (LQG) attempts to unify general relativity with quantum physics to offer a complete description of the universe by quantising spacetime geometry, but the numerical calculations we encounter are extraordinarily difficult. Progress has been made in the covariant formulation of LQG, but the tools do not carry over to the canonical formulation. These tools are graphical by nature, describing space with spin networks to make calculations in LQG more intuitive to the human hand. Recently, a new notation for working with spin networks has been used by arXiv:2412.20272 to offer the first accurate numerical results in canonical LQG by allowing the underlying graphs to change throughout the calculation, though they are forced to concede visual intuitiveness. In this thesis, we offer a more radical rephrasing of spin network calculations by translating them into the finite-dimensional ZX-calculus, extending previous attempts to translate into the standard (qubit) ZX-calculus (arXiv:2111.03114). Specifically, we derive the mixed-dimensional ZX-diagrams representing the generating objects of spin networks and the rules for the Penrose Spin Calculus (arXiv:2511.06012), and use these to present the ZX-form and correctness of "loop removal". We also derive the forms for several fundamental LQG objects in the finite-dimensional ZX-calculus for the first time. This gives us a high-level, intuitive graphical language that retains a flexibility to handle changing graph structures, and thus we argue positions the PSC as the new definitive language for canonical LQG. Furthermore, we investigate the possibility for a matrix-like normal form for spin networks deriving from a novel perspective of the PSC in terms of W-nodes.

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  1. [] - Title: Thermal Vacuum Model for Cosmology without Inflaton - Robert Alicki

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