Fri - 12/27/24

**Title:

      Covariant LTB collapse in models of loop quantum gravity**  - **Authors:** Martin Bojowald, Erick I. Duque, Dennis Hartmann  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  Models of gravitational collapse provide important means to test whether non-classical space-time effects motivated for instance by quantum gravity can be realized in generic ways in physically relevant situations. Here, a detailed analysis of marginally bound Lemaitre-Tolman-Bondi space-times is given in emergent modified gravity, which in particular includes a covariant formulation of holonomy modifications usually considered in models of loop quantum gravity. As a result, generic collapse in this setting is shown to imply a physical singularity that removes the bouncing behavior seen in vacuum space-times with the same type of modifications.

There is no new related paper today

Thu - 12/26/24

**Title:

      Covariant LTB collapse in models of loop quantum gravity**  - **Authors:** Martin Bojowald, Erick I. Duque, Dennis Hartmann  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  Models of gravitational collapse provide important means to test whether non-classical space-time effects motivated for instance by quantum gravity can be realized in generic ways in physically relevant situations. Here, a detailed analysis of marginally bound Lemaitre-Tolman-Bondi space-times is given in emergent modified gravity, which in particular includes a covariant formulation of holonomy modifications usually considered in models of loop quantum gravity. As a result, generic collapse in this setting is shown to imply a physical singularity that removes the bouncing behavior seen in vacuum space-times with the same type of modifications.

There is no new related paper today

Wed - 12/25/24

**Title:

      Testing loop quantum gravity by quasi-periodic oscillations: rotating blackholes**  - **Authors:** Jafar Khodagholizadeh, Ghadir Jafari, Alireza Allahyari, Ali Vahedi  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We investigate a compelling model of a rotating black hole that is deformed by the effects of loop quantum gravity (LQG). We present a simplified metric and explore two distinct geometries: one in which the masses of the black hole and white hole are equal, and another in which they differ. Our analysis yields the radius of the innermost stable circular orbits (ISCO), as well as the energy and angular momentum of a particle within this framework. Additionally, we find the frequency of the first-order resonance separately. We constrain the model by the quasi-periodic oscillations (QPO) of the X-ray binary GRO J1655-40. We show that $\lambda=0.15^{+0.23}_{-0.14}$ at $1\sigma$ confidence level for equal mass black hole and white hole geometry. For the other geometry we get $\lambda=0.11^{+0.07}_{-0.07}$ at $1\sigma$ confidence this http URL encounter a degeneracy in the parameter space that hinders our ability to constrain $\lambda$ with greater precision.

There is no new related paper today

Tue - 12/24/24

**Title:

      One-loop corrections to near extremal Kerr thermodynamics from semiclassical Virasoro blocks**  - **Authors:** Paolo Arnaudo, Giulio Bonelli, Alessandro Tanzini  - **Subjects:** Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  We propose a method to perform an exact calculation of one-loop quantum corrections to black hole entropy in terms of Virasoro semiclassical blocks. We analyse in detail four-dimensional Kerr black hole and show that in the near-extremal limit a branch of long-lived modes arises. We prove that the contribution of these modes accounts for a $(s-1/2)\log T_{\text{Hawking}}$ correction to the entropy for massless particles of spin $s=1,2$. We show that in the full calculation performed in the exact Kerr background the leading contribution actually is sourced by the near-horizon region only, and as such has a universal validity for any asymptotic behavior at infinity.

There is no new related paper today

  1. [] - Title: On the Cutoff Scale Identification of FLRW Cosmology in Asymptotically Safe Gravity - Chiang-Mei Chen, Rituparna Mandal, Nobuyoshi Ohta

Mon - 12/23/24

**Title:

      Relational Observables in Group Field Theory**  - **Authors:** Luca Marchetti, Edward Wilson-Ewing  - **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 construct relational observables in group field theory (GFT) in terms of covariant positive operator-valued measures (POVMs), using techniques developed in the context of quantum reference frames. We focus on matter quantum reference frames; this can be generalized to other types of frames within the same POVM-based framework. The resulting family of relational observables provides a covariant framework to extract localized observables from GFT, which is typically defined in a perspective-neutral way. Then, we compare this formalism with previous proposals for relational observables in GFT. We find that our quantum reference frame-based relational observables overcome the intrinsic limitations of previous proposals while reproducing the same continuum limit results concerning expectation values of the number and volume operators on coherent states. Nonetheless, there can be important differences for more complex operators, as well as for other types of GFT states. Finally, we also use a specific class of POVMs to show how to project states and operators from the more general perspective-neutral GFT Fock space to a perspective-dependent one where a scalar matter field plays the role of a relational clock.

There is no new related paper today

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