Fri - 06/27/25

There is no new related paper today

There is no new related paper today

  1. [] - Title: Holography with Null Boundaries - Christian Ferko, Savdeep Sethi

Thu - 06/26/25

**Title:

      Emergent Lorentzian Geometries from Spin-Foams and Group Field Theories**  - **Authors:** Alexander F. Jercher  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  The emergence of Lorentzian geometries in spin-foams and group field theories is investigated. The spectral dimension of periodic Euclidean spin-foam frusta is studied. At large scales, the spectral dimension is generically four. At lower scales, a non-trivial flow of the spectral dimension is observed, sensitive to quantum effects, curvature induced oscillations and the parameters of the theory. The removal of numerical cutoffs and a thermodynamic limit is discussed, suggesting a phase transition from zero to four large-scale dimensions. Lorentzian Regge calculus for (3+1) cosmology, modelled with Lorentzian 4-frusta, coupled to a massless free scalar field is studied. It is shown that causal regularity, solutions to the Regge equations and a continuum limit only exist if the cells connecting neighboring slices are timelike. The dynamics can be expressed relationally only in the small deficit angle limit. Effective (2+1) spin-foam cosmology with a minimally coupled massive scalar field is investigated. The scalar field mass is shown to ensure convergence of the path integral. The classicality of expectation values is shown to be intimately connected to causal regularity and the path integral measure. A causal completion of the Barrett-Crane group field theory model is developed. Its amplitudes are explicitly computed in spin representation using methods from integral geometry. A Landau-Ginzburg analysis is applied to the complete Barrett-Crane (BC) group field theory model. It is shown that mean-field theory is generically self-consistent, and that timelike faces do not contribute to the critical behavior. Employing the complete BC model, a physical Lorentzian reference frame is coupled, and scalar cosmological perturbations are extracted from entangled GFT coherent states. The dynamics of these perturbations are shown to agree with classical results up to quantum corrections.

**Title:

      Emergent Lorentzian Geometries from Spin-Foams and Group Field Theories**  - **Authors:** Alexander F. Jercher  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  The emergence of Lorentzian geometries in spin-foams and group field theories is investigated. The spectral dimension of periodic Euclidean spin-foam frusta is studied. At large scales, the spectral dimension is generically four. At lower scales, a non-trivial flow of the spectral dimension is observed, sensitive to quantum effects, curvature induced oscillations and the parameters of the theory. The removal of numerical cutoffs and a thermodynamic limit is discussed, suggesting a phase transition from zero to four large-scale dimensions. Lorentzian Regge calculus for (3+1) cosmology, modelled with Lorentzian 4-frusta, coupled to a massless free scalar field is studied. It is shown that causal regularity, solutions to the Regge equations and a continuum limit only exist if the cells connecting neighboring slices are timelike. The dynamics can be expressed relationally only in the small deficit angle limit. Effective (2+1) spin-foam cosmology with a minimally coupled massive scalar field is investigated. The scalar field mass is shown to ensure convergence of the path integral. The classicality of expectation values is shown to be intimately connected to causal regularity and the path integral measure. A causal completion of the Barrett-Crane group field theory model is developed. Its amplitudes are explicitly computed in spin representation using methods from integral geometry. A Landau-Ginzburg analysis is applied to the complete Barrett-Crane (BC) group field theory model. It is shown that mean-field theory is generically self-consistent, and that timelike faces do not contribute to the critical behavior. Employing the complete BC model, a physical Lorentzian reference frame is coupled, and scalar cosmological perturbations are extracted from entangled GFT coherent states. The dynamics of these perturbations are shown to agree with classical results up to quantum corrections.

Wed - 06/25/25

**Title:

      Nonlocal correlations for semiclassical states in loop quantum gravity**  - **Authors:** Filipe H. C. Menezes, Nelson Yokomizo  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We compute the two-point correlation function of the area operator for semiclassical states of loop quantum gravity in the limit of large spins. The cases of intrinsic and extrinsic coherent states are considered, along with a new class of semiclassical states constructed as perturbations of Livine-Speziale coherent states. For the usual coherent states, the correlations are shown to be short-ranged, decaying exponentially with the distance. Introducing perturbations given by correlated elementary excitations and decays of the gravitational field along pairs of loops, we obtain new states that, while preserving the peakedness properties of the unperturbed states, can also display long-ranged correlations. The perturbed coherent states include examples reproducing the typical decay of correlations for quantum fluctuations of the geometry associated with free gravitons on a background metric. Such a behavior is a natural requirement for the compatibility of semiclassical states in quantum gravity with the physical regime pictured by perturbative quantum gravity.

There is no new related paper today

Tue - 06/24/25

There is no new related paper today

There is no new related paper today

  1. [] - Title: Quasi-normal modes and shadows of scale-dependent regular black holes - Benjamin Koch, Gonzalo J. Olmo, Ali Riahinia, Ángel Rincón, Diego Rubiera-Garcia

Mon - 06/23/25

There is no new related paper today

There is no new related paper today

  1. [] - Title: Regular Vaidya solutions of effective gravitational theories - Valentin Boyanov, Raúl Carballo-Rubio

New papers last week