Fri - 05/24/24

**Title:

      Constraining regularization ambiguities in Loop Quantum Cosmology via CMB**  - **Authors:** Bao-Fei Li, Meysam Motaharfar, Parampreet Singh  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  In order to investigate the potential observational signals of different regularization ambiguities in loop quantum cosmological models, we systematically compute and compare the primordial scalar power spectra and the resulting angular power spectra in the standard loop quantum cosmology (LQC) and its Thiemann regularized versions -- modified LQC-I/II (mLQC-I/II), using both the dressed metric and the hybrid approaches. All three loop quantum cosmological models yield a non-singular bounce with a post-bounce physics that converges rapidly in a few Planck seconds. Using Starobinsky potential and the initial conditions for the background dynamics chosen to yield the same inflationary e-foldings, which are fixed to be $65$ in all three LQC models, we require that all three models result in the same scale-invariant regime for the primordial power spectrum with a relative difference of less than one percent. This permits us to explore the differences resulting from the deep Planck regime in the angular power spectrum. For the adiabatic states, our results demonstrate that the angular power spectrum predicted by the hybrid approach has a smaller deviation from the angular power spectrum predicted by the standard $\Lambda$CDM cosmological model at large angles in comparison with the dressed metric approach for all three models. The angular power spectrum predicted by mLQC-I in both the hybrid and the dressed metric approaches shows the smallest deviation from the one predicted by the standard $\Lambda$CDM cosmological model at large angular scales, except for the case of fourth order adiabatic initial states in the hybrid approach. On the contrary, mLQC-II results in the largest deviations for the amplitude of the angular power spectrum at large angles and is most disfavored.

There is no new related paper today

Thu - 05/23/24

**Title:

      Constraining regularization ambiguities in Loop Quantum Cosmology via CMB**  - **Authors:** Bao-Fei Li, Meysam Motaharfar, Parampreet Singh  - **Subjects:** Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)  - **Arxiv link:** [https://arxiv.org/abs/](https://arxiv.org/abs/)  - **Abstract**  In order to investigate the potential observational signals of different regularization ambiguities in loop quantum cosmological models, we systematically compute and compare the primordial scalar power spectra and the resulting angular power spectra in the standard loop quantum cosmology (LQC) and its Thiemann regularized versions -- modified LQC-I/II (mLQC-I/II), using both the dressed metric and the hybrid approaches. All three loop quantum cosmological models yield a non-singular bounce with a post-bounce physics that converges rapidly in a few Planck seconds. Using Starobinsky potential and the initial conditions for the background dynamics chosen to yield the same inflationary e-foldings, which are fixed to be $65$ in all three LQC models, we require that all three models result in the same scale-invariant regime for the primordial power spectrum with a relative difference of less than one percent. This permits us to explore the differences resulting from the deep Planck regime in the angular power spectrum. For the adiabatic states, our results demonstrate that the angular power spectrum predicted by the hybrid approach has a smaller deviation from the angular power spectrum predicted by the standard $\Lambda$CDM cosmological model at large angles in comparison with the dressed metric approach for all three models. The angular power spectrum predicted by mLQC-I in both the hybrid and the dressed metric approaches shows the smallest deviation from the one predicted by the standard $\Lambda$CDM cosmological model at large angular scales, except for the case of fourth order adiabatic initial states in the hybrid approach. On the contrary, mLQC-II results in the largest deviations for the amplitude of the angular power spectrum at large angles and is most disfavored.

There is no new related paper today

Fri - 05/17/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: All-order splits and multi-soft limits for particle and string amplitudes - Nima Arkani-Hamed, Carolina Figueiredo

Thu - 05/16/24

**Title:

      Time Evolution in Canonical Quantum Gravity is Trivial**  - **Authors:** Ali Kaya  - **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**  The Wheeler-DeWitt equation does not describe any explicit time evolution of the wave function, and somehow related to this issue, there is no natural way of defining an invariant inner product that provides a viable probability interpretation. We show that both of these difficulties are solved in a covariant canonical formulation of general relativity where the configuration space is extended by introducing the embedding coordinates as dynamical variables. The formalism describes the evolution of the wave function from one spacelike slice to another, but as in the case of spatial diffeomorphisms this is simply implemented by a coordinate change in the wave function. We demonstrate how the time equation disappears after gauge fixing that removes the embedding coordinates. These findings indicate that the time evolution is trivial in a background independent formulation of quantum gravity.

There is no new related paper today

Wed - 05/15/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: Schwarzschild black hole revisited: Before the complete collapse - J. Ovalle

Tue - 05/14/24

**Title:

      Quasinormal Frequencies of Fields with Various Spin in the Quantum Oppenheimer-Snyder Model of Black Holes**  - **Authors:** Milena Skvortsova  - **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**  A recent development involves an intriguing model of a quantum-corrected black hole, established through the application of the quantum Oppenheimer-Snyder model within loop quantum cosmology [Lewandowski et al., Phys. Rev. Lett. 130 (2023) 10, 101501]. Employing both time-domain integration and the WKB approach, we compute the quasinormal frequencies for scalar, electromagnetic, and neutrino perturbations in these quantum-corrected black holes. Our analysis reveals that while the real oscillation frequencies undergo only minor adjustments due to the quantum parameter, the damping rate experiences a significant decrease as a result of its influence. We also deduce the analytic formula for quasinormal frequencies in the eikonal limit and show that the correspondence between the null geodesics and eikoanl quasinormal modes holds in this case.

There is no new related paper today

Mon - 05/13/24

There is no new related paper today

There is no new related paper today

  1. [] - Title: Non-singular black hole by gravitational decoupling and some thermodynamic properties - Maxim Misyura, Angel Rincon, Vitalii Vertogradov

New papers last week