Fri - 11/15/24

There is no new related paper today

**Title:

      (2+1) Lorentzian quantum cosmology from spin-foams: chances and obstacles for semi-classicality**  - **Authors:** Alexander F. Jercher, José Diogo Simão, Sebastian Steinhausa  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We construct an effective cosmological spin-foam model for a (2+1) dimensional spatially flat universe, discretized on a hypercubical lattice, containing both space- and time-like regions. Our starting point is the recently proposed coherent state spin-foam model for (2+1) Lorentzian quantum gravity. The full amplitude is assumed to factorize into single vertex amplitudes with boundary data corresponding to Lorentzian 3-frusta. A stationary phase approximation is performed at each vertex individually, where the inverse square root of the Hessian determinant serves as a measure for the effective path integral. Additionally, a massive scalar field is coupled to the geometry, and we show that its mass renders the partition function convergent. For a single 3-frustum with time-like struts, we compute the expectation value of the bulk strut length and show that it generically agrees with the classical solutions and that it is a discontinuous function of the scalar field mass. Allowing the struts to be space-like introduces causality violations, which drive the expectation values away from the classical solutions due to the lack of an exponential suppression of these configurations. This is a direct consequence of the semi-classical amplitude only containing the real part of deficit angles, in contrast with the Lorentzian Regge action used in effective spin-foams. We give an outlook on how to evaluate the partition function on an extended discretization including a bulk spatial slice. This serves as a foundation for future investigations of physically interesting scenarios such as a quantum bounce or the viability of massive scalar field clocks. Our results demonstrate that the effective path integral in the causally regular sector serves as a viable quantum cosmology model, but that the agreement of expectation values with classical solutions is tightly bound to the path integral measure.

Thu - 11/14/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: Emergent Geometry from Quantum Probability - Shadi Ali Ahmad, Marc S. Klinger

Wed - 11/13/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: The thermodynamic profile of AdS black holes in Lorentz invariance-violating Bumblebee and Kalb-Ramond gravity - Syed Masood, Said Mikki

Tue - 11/12/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: Echoes from Beyond: Detecting Gravitational Wave Quantum Imprints with LISA - Nils Deppe, Lavinia Heisenberg, Henri Inchauspé, Lawrence E. Kidder, David Maibach, Sizheng Ma, Jordan Moxon, Kyle C. Nelli, William Throwe, Nils L. Vu

Mon - 11/11/24

There is no new related paper today

**Title:

      Tannakian QFT: from spark algebras to quantum groups**  - **Authors:** Tudor Dimofte, Wenjun Niu  - **Subjects:** Subjects: High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph); Quantum Algebra (math.QA); Representation Theory (math.RT)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We propose a nonperturbative construction of Hopf algebras that represent categories of line operators in topological quantum field theory, in terms of semi-extended operators (spark algebras) on pairs of transverse topological boundary conditions. The construction is a direct implementation of Tannakian formalism in QFT. Focusing on d=3 dimensional theories, we find topological definitions of R-matrices, ribbon twists, and the Drinfeld double construction for generalized quantum groups. We illustrate our construction in finite-group gauge theory, and apply it to obtain new results for B-twisted 3d $\mathcal{N}=4$ gauge theories, a.k.a. equivariant Rozansky-Witten theory, or supergroup BF theory (including ordinary BF theory with compact gauge group). We reformulate our construction mathematically in terms of abelian and dg tensor categories, and discuss connections with Koszul duality.
  1. [] - Title: Frame-dragging effects in the gravitational quantum field theory - Dongfeng Gao, Wei-Tou Ni

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