Fri - 01/06/23

There is no new related paper today

There is no new related paper today

  1. [2301.01810] - Celestial Holography Revisited - Charlotte Sleight, Massimo Taronna

Thu - 01/05/23

Regular black holes from Loop Quantum Gravity

  • Authors: Abhay Ashtekar, Javier Olmedo, Parampreet Singh
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Mathematical Physics (math-ph)
  • Arxiv link: https://arxiv.org/abs/2301.01309
  • Abstract There is rich literature on regular black holes from loop quantum gravity (LQG), where quantum geometry effects resolve the singularity, leading to a quantum extension of the classical space-time. As we will see, the mechanism that resolves the singularity can also trigger conceptually undesirable features that can be subtle and are often uncovered only after a detailed examination. Therefore, the quantization scheme has to be chosen rather astutely. We illustrate the new physics that emerges first in the context of the eternal black hole represented by the Kruskal space-time in classical general relativity, then in dynamical situations involving gravitational collapse, and finally, during the Hawking evaporation process. The emphasis is on novel conceptual features associated with the causal structure, trapping and anti-trapping horizons and boundedness of invariants associated with curvature and matter. This Chapter is not intended to be an exhaustive account of all LQG results on non-singular black holes. Rather, we have selected a few main-stream thrusts to anchor the discussion, and provided references where further details as well as discussions of related developments can be found. In the spirit of this Volume, the goal is to present a bird’s eye view that is accessible to a broad audience.

There is no new related paper today

Wed - 01/04/23

Generalised (non-singular) entropy functions with applications to cosmology and black holes

  • Authors: Sergei D. Odintsov, Tanmoy Paul
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2301.01013
  • Abstract The growing interest of different entropy functions proposed so far (like the Bekenstein-Hawking, Tsallis, R'{e}nyi, Barrow, Sharma-Mittal, Kaniadakis and Loop Quantum Gravity entropies) towards black hole thermodynamics as well as towards cosmology lead to the natural question that whether there exists a generalized entropy function that can generalize all these known entropies. With this spirit, we propose a new 4-parameter entropy function that seems to converge to the aforementioned known entropies for certain limits of the entropic parameters. The proposal of generalized entropy is extended to non-singular case, in which case, the entropy proves to be singular-free during the entire cosmological evolution of the universe. The hallmark of such generalized entropies is that it helps us to fundamentally understand one of the important physical quantities namely ``entropy’’. Consequently we address the implications of the generalized entropies on black hole thermodynamics as well as on cosmology, and discuss various constraints of the entropic parameters from different perspectives.

There is no new related paper today

Tue - 01/03/23

There is no new related paper today

There is no new related paper today

  1. [2301.00777] - Non-Invertible Symmetries in Supergravity - Eduardo García-Valdecasas

Mon - 01/02/23

Tunneling wavefunction proposal with loop quantum geometry effects

  • Authors: Meysam Motaharfar, Parampreet Singh
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.14065
  • Abstract In Vilenkin’s tunneling wavefunction proposal our expanding universe is born via a tunneling through a barrier from nothing at the zero scale factor. We explore the viability of this proposal for the spatially closed FLRW model with a positive cosmological constant including quantum gravity modifications in the Planck regime. Our setting is the effective spacetime description of loop quantum cosmology (LQC) which is known to replace the big bang singularity with a bounce due to the holonomy modifications. Due to the bounce, the barrier potential of the Wheeler-DeWitt theory is replaced by a step like potential which makes the tunneling proposal incompatible. But for a complete picture of singularity resolution, inverse scale factor modifications from quantum geometry must be included which play an important role at very small scale factors in the spatially closed models. We show that with inclusion of inverse scale factor modifications the resulting potential is again a barrier potential. The universe at the vanishing scale factor is dynamically non-singular and in an Einstein static like phase. We show that quantum geometric effects in LQC provide a non-singular completion of Vilenkin’s tunneling proposal. We also find that quantum geometric effects result in a possibility of a tunneling to a quantum cyclic universe albeit for a very large value of cosmological constant determined by the quantum geometry.

Non-existence of quantum black hole horizons in the improved dynamics approach

  • Authors: Wen-Cong Gan, Xiao-Mei Kuang, Zhen-Hao Yang, Yungui Gong, Anzhong Wang, Bin Wang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.14535
  • Abstract In this paper, we study the quantum geometric effects near the locations that black hole horizons used to appear in the classical theory within the framework of the improved dynamic approach, in which the two polymerization parameters of the Kantowski-Sachs spacetime are functions of the phase variables. Our detailed analysis shows that the effects are so strong that black hole horizons of the effective quantum theory do not exist any longer, and the corresponding Kantowski-Sachs model now describes the entire spacetime of the trapped region, instead of being only the internal region of a black hole, as it is usually expected in loop quantum gravity.

Spinfoams and high performance computing

  • Authors: Pietro Dona, Muxin Han, Hongguang Liu
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.14396
  • Abstract Numerical methods are a powerful tool for doing calculations in spinfoam theory. We review the major frameworks available, their definition, and various applications. We start from $\texttt{sl2cfoam-next}$, the state-of-the-art library to efficiently compute EPRL spin foam amplitudes based on the booster decomposition. We also review two alternative approaches based on the integration representation of the spinfoam amplitude: Firstly, the numerical computations of the complex critical points discover the curved geometries from the spinfoam amplitude and provides important evidence of resolving the flatness problem in the spinfoam theory. Lastly, we review the numerical estimation of observable expectation values based on the Lefschetz thimble and Markov-Chain Monte Carlo method, with the EPRL spinfoam propagator as an example.

  1. [2212.14488] - Motion of a superfluid vortex according to holographic quantum dissipation - Wei-Can Yang, Chuan-Yin Xia, Hua-Bi Zeng, Makoto Tsubota, Jan Zaanen

  2. [2212.14605] - Obstructions to Gapped Phases from Non-Invertible Symmetries - Anuj Apte, Clay Cordova, Ho Tat Lam

  3. [2212.14753] - Islands in the Proliferating de Sitter Space - Jong-Hyun Baek, Kang-Sin Choi

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