Fri - 08/29/25

There is no new related paper today

There is no new related paper today

  1. [] - Title: TASI lectures on Matrix Theory from a modern viewpoint - Henry W. Lin

Thu - 08/28/25

**Title:

      Causal Viscous Fluids and Non-Singular Cosmological Bounces**  - **Authors:** L. Yildiz, D. Kayki, E. Gudekli  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We investigate the realization of non-singular bouncing cosmologies driven by causal bulk-viscous fluids within General Relativity, $f(R)$ gravity, and Loop Quantum Cosmology. Building on the no-go result of Eckart theory in spatially flat universes, we show that the Israel--Stewart formulation, which incorporates finite relaxation times, permits controlled violations of the null energy condition at the bounce while remaining consistent with thermodynamic and causality requirements. Analytical bounce solutions are constructed from parametrized scale factors, yielding explicit constraints on the viscosity coefficient and relaxation time that guarantee positive entropy production and stable perturbations. In extended gravity frameworks, we demonstrate that higher-curvature corrections in $f(R)$ models and quantum geometry effects in Loop Quantum Cosmology further enhance the robustness of viscous bounces. Our results establish a unified description in which bulk viscosity provides a physically consistent mechanism for singularity resolution across different theories of gravity, highlighting distinctive conditions under which smooth cosmological bounces can occur.

There is no new related paper today

Wed - 08/27/25

**Title:

      ER = EPR in Loop Quantum Gravity: the Immirzi Parameter and the Continuum Limit**  - **Authors:** Fabrizio Tamburini  - **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**  We recast the finite-region analysis of Einstein's equations that underpins the ER=EPR program into the loop quantum gravity (LQG) framework. By translating curvature-energy uncertainty relations into holonomy-flux kinematics, and by identifying Planckian Einstein-Rosen throats with single-puncture cuts through spin networks, we obtain a precise dictionary between entanglement and quantum geometry. Within this dictionary we derive the Barbero-Immirzi parameter directly from the entanglement/area increment of a minimal bridge, and show that a boundary edge-mode construction renders the Bekenstein - Hawking entropy coefficient universal and independent of $\gamma$ under a natural complex polarization. We further establish a refinement renormalization flow for spin-foam amplitudes driven by the finite-region curvature energy bound, which suppresses bubble divergences and yields a regulator-independent continuum limit under explicit conditions. Finally, we indicate observational consequences that follow from an $N$-party generalized uncertainty relation.

**Title:

      ER = EPR in Loop Quantum Gravity: the Immirzi Parameter and the Continuum Limit**  - **Authors:** Fabrizio Tamburini  - **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**  We recast the finite-region analysis of Einstein's equations that underpins the ER=EPR program into the loop quantum gravity (LQG) framework. By translating curvature-energy uncertainty relations into holonomy-flux kinematics, and by identifying Planckian Einstein-Rosen throats with single-puncture cuts through spin networks, we obtain a precise dictionary between entanglement and quantum geometry. Within this dictionary we derive the Barbero-Immirzi parameter directly from the entanglement/area increment of a minimal bridge, and show that a boundary edge-mode construction renders the Bekenstein - Hawking entropy coefficient universal and independent of $\gamma$ under a natural complex polarization. We further establish a refinement renormalization flow for spin-foam amplitudes driven by the finite-region curvature energy bound, which suppresses bubble divergences and yields a regulator-independent continuum limit under explicit conditions. Finally, we indicate observational consequences that follow from an $N$-party generalized uncertainty relation.

Tue - 08/26/25

**Title:

      Interacting Scalar Field Cosmology from Full Quantum Gravity**  - **Authors:** Tom R. Ladstätter, Luca Marchetti  - **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 study the relational cosmological dynamics emerging from interacting group field theory (GFT) models minimally coupled to a massless clock scalar field and a self-interacting scalar field. We focus on two broad classes of GFT interactions - pseudosimplicial and pseudotensorial - which generalize simplicial and tensorial interactions, respectively. Treating these interactions perturbatively, we extract the effective cosmological dynamics using mean-field techniques. In the geometric sector, we identify appropriate classical limits of the resulting dynamics, characterized by the emergence of a cosmological constant term in pseudotensorial models and of dynamical dark energy in pseudosimplicial ones. In the matter sector, we find that quantum gravity interactions induce a mass term and modify the classical symmetries of the scalar field dynamics, allowing for a consistent classical matter-geometry description only for specific forms of the effective scalar field potential. Finally, we show that these quantum gravity compatibility conditions on the effective potentials can be relaxed by allowing for a scale-dependent gravitational coupling, and that this running is uniquely fixed once the classical scalar field potential is specified.

There is no new related paper today

Mon - 08/25/25

**Title:

      Interacting Scalar Field Cosmology from Full Quantum Gravity**  - **Authors:** Tom R. Ladstätter, Luca Marchetti  - **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 study the relational cosmological dynamics emerging from interacting group field theory (GFT) models minimally coupled to a massless clock scalar field and a self-interacting scalar field. We focus on two broad classes of GFT interactions - pseudosimplicial and pseudotensorial - which generalize simplicial and tensorial interactions, respectively. Treating these interactions perturbatively, we extract the effective cosmological dynamics using mean-field techniques. In the geometric sector, we identify appropriate classical limits of the resulting dynamics, characterized by the emergence of a cosmological constant term in pseudotensorial models and of dynamical dark energy in pseudosimplicial ones. In the matter sector, we find that quantum gravity interactions induce a mass term and modify the classical symmetries of the scalar field dynamics, allowing for a consistent classical matter-geometry description only for specific forms of the effective scalar field potential. Finally, we show that these quantum gravity compatibility conditions on the effective potentials can be relaxed by allowing for a scale-dependent gravitational coupling, and that this running is uniquely fixed once the classical scalar field potential is specified.

There is no new related paper today

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