Fri - 12/30/22

Black Hole Entropy in Loop Quantum Gravity

  • Authors: J. Fernando Barbero G., Daniele Pranzetti
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13469
  • Abstract We give an account of the state of the art about black hole entropy in Loop Quantum Gravity. This chapter contains a historical summary and explains how black hole entropy is described by relying on the concept of isolated horizon, with an emphasis on different representations of its associated symmetry group. It continues with a review of the combinatorial methods necessary to understand the behavior of the entropy as a function of the area and concludes with a discussion of the nature of the quantum horizon degrees of freedom that account for the black hole entropy and the related issue of the fixing of the Immirzi parameter.

An algebraic approach to the “frozen formalism” problem of time

  • Authors: Martin Bojowald, Artur Tsobanjan
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13961
  • Abstract The long-standing problem of time in canonical quantum gravity is the source of several conceptual and technical issues. Here, recent mathematical results are used to provide a consistent algebraic formulation of dynamical symplectic reduction that avoids difficult requirements such as the computation of a complete set of Dirac observables or the construction of a physical Hilbert space. In addition, the new algebraic treatment makes it possible to implement a consistent realization of the gauge structure off the constraint surface. As a consequence, previously unrecognized consistency conditions are imposed on deparameterization – the method traditionally used to unfreeze evolution in completely constrained systems. A detailed discussion of how the new formulation extends previous semiclassical results shows that an internal time degree of freedom need not be semiclassical in order to define a consistent quantum evolution.

On the discrete version of the Kerr-Newman solution

  • Authors: V.M. Khatsymovsky
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13547
  • Abstract This paper continues our work on black holes in the framework of the Regge calculus, where the discrete version (with a certain edge length scale $b$ proportional to the Planck scale) of the classical solution emerges as an optimal starting point for the perturbative expansion after functional integration over the connection, with the singularity resolved. An interest in the present discrete Kerr-Newman type solution (with the parameter $a \gg b$) may be to check the classical prediction that the electromagnetic contribution to the metric and curvature on the singularity ring is (infinitely) greater than the contribution of the $\delta$-function-like mass distribution, no matter how small the electric charge is. Here we encounter a kind of a discrete diagram technique, but with three-dimensional (static) diagrams and with only a few diagrams, although with modified (extended to complex coordinates) propagators. The metric (curvature) in the vicinity of the former singularity ring is considered. The electromagnetic contribution does indeed have a relative factor that is infinite at $b \to 0$, but, taking into account some existing estimates of the upper bound on the electric charge of known substances, it is not so large for habitual bodies and can only be significant for practically non-rotating black holes.

  1. [2212.13357] - Novel black holes in higher derivative gravity - Yang Huang, Dao-Jun Liu, Hongsheng Zhang

  2. [2212.13561] - Bouncing Cosmology in VCDM - Alexander Ganz, Paul Martens, Shinji Mukohyama, Ryo Namba

  3. [2212.14010] - Quantum Gravity Fluctuations in the Timelike Raychaudhuri Equation - Sang-Eon Bak, Maulik Parikh, Sudipta Sarkar, Francesco Setti

  4. [2212.13266] - Subalgebra-subregion duality: emergence of space and time in holography - Samuel Leutheusser, Hong Liu

  5. [2212.13586] - Entanglement Entropy and Causal Set Theory - Yasaman K. Yazdi

  6. [2212.13639] - Holographic thermal propagator for low scale dimensions - Borut Bajc, Adrian R. Lugo

  7. [2212.14011] - Massless graviton in a model of quantum gravity with emergent spacetime - Sung-Sik Lee

Thu - 12/29/22

Black Hole Entropy in Loop Quantum Gravity

  • Authors: J. Fernando Barbero G., Daniele Pranzetti
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13469
  • Abstract We give an account of the state of the art about black hole entropy in Loop Quantum Gravity. This chapter contains a historical summary and explains how black hole entropy is described by relying on the concept of isolated horizon, with an emphasis on different representations of its associated symmetry group. It continues with a review of the combinatorial methods necessary to understand the behavior of the entropy as a function of the area and concludes with a discussion of the nature of the quantum horizon degrees of freedom that account for the black hole entropy and the related issue of the fixing of the Immirzi parameter.

An algebraic approach to the “frozen formalism” problem of time

  • Authors: Martin Bojowald, Artur Tsobanjan
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13961
  • Abstract The long-standing problem of time in canonical quantum gravity is the source of several conceptual and technical issues. Here, recent mathematical results are used to provide a consistent algebraic formulation of dynamical symplectic reduction that avoids difficult requirements such as the computation of a complete set of Dirac observables or the construction of a physical Hilbert space. In addition, the new algebraic treatment makes it possible to implement a consistent realization of the gauge structure off the constraint surface. As a consequence, previously unrecognized consistency conditions are imposed on deparameterization – the method traditionally used to unfreeze evolution in completely constrained systems. A detailed discussion of how the new formulation extends previous semiclassical results shows that an internal time degree of freedom need not be semiclassical in order to define a consistent quantum evolution.

On the discrete version of the Kerr-Newman solution

  • Authors: V.M. Khatsymovsky
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13547
  • Abstract This paper continues our work on black holes in the framework of the Regge calculus, where the discrete version (with a certain edge length scale $b$ proportional to the Planck scale) of the classical solution emerges as an optimal starting point for the perturbative expansion after functional integration over the connection, with the singularity resolved. An interest in the present discrete Kerr-Newman type solution (with the parameter $a \gg b$) may be to check the classical prediction that the electromagnetic contribution to the metric and curvature on the singularity ring is (infinitely) greater than the contribution of the $\delta$-function-like mass distribution, no matter how small the electric charge is. Here we encounter a kind of a discrete diagram technique, but with three-dimensional (static) diagrams and with only a few diagrams, although with modified (extended to complex coordinates) propagators. The metric (curvature) in the vicinity of the former singularity ring is considered. The electromagnetic contribution does indeed have a relative factor that is infinite at $b \to 0$, but, taking into account some existing estimates of the upper bound on the electric charge of known substances, it is not so large for habitual bodies and can only be significant for practically non-rotating black holes.

  1. [2212.13357] - Novel black holes in higher derivative gravity - Yang Huang, Dao-Jun Liu, Hongsheng Zhang

  2. [2212.13561] - Bouncing Cosmology in VCDM - Alexander Ganz, Paul Martens, Shinji Mukohyama, Ryo Namba

  3. [2212.14010] - Quantum Gravity Fluctuations in the Timelike Raychaudhuri Equation - Sang-Eon Bak, Maulik Parikh, Sudipta Sarkar, Francesco Setti

  4. [2212.13266] - Subalgebra-subregion duality: emergence of space and time in holography - Samuel Leutheusser, Hong Liu

  5. [2212.13586] - Entanglement Entropy and Causal Set Theory - Yasaman K. Yazdi

  6. [2212.13639] - Holographic thermal propagator for low scale dimensions - Borut Bajc, Adrian R. Lugo

  7. [2212.14011] - Massless graviton in a model of quantum gravity with emergent spacetime - Sung-Sik Lee

Wed - 12/28/22

Loop quantum cosmological model from ADM Hamiltonian

  • Authors: You Ding, Xiangdong Zhang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13159
  • Abstract The loop quantum cosmological model from ADM Hamiltonian is studied in this paper. We consider the spatially flat homogeneous FRW model. It turns out that the modified Friedmann equation keeps the same form as the APS LQC model. However, the critical matter density for the bounce point is only a quarter of the previous APS model, i.e. $\rho_{cL}=\frac{\rho_c}{4}$. This is interesting because the lower critical bounce density means the quantum gravity effects will get involved earlier than the previous LQC model. Besides, the lower critical density also means the detection of quantum gravity effects easier than the previous model.

An extension of the $\mathrm{U}!\left(1\right)$ BF theory, Turaev-Viro invariant and Drinfeld center construction. Part I: Quantum fields, quantum currents and Pontryagin duality

  • Authors: Emil Høssjer, Philippe Mathieu, Frank Thuillier
  • Subjects: Mathematical Physics (math-ph); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.12872
  • Abstract In this first of a series of articles dedicated to natural extensions of the U(1) BF theory, abelian Turaev-Viro (TV) construction and corresponding Drinfeld center construction for any closed oriented smooth manifolds, we present the mathematical background that will be used.

  1. [2212.13031] - Approximately stealth black hole in higher-order scalar-tensor theories - Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi

  2. [2212.13109] - The causality road from dynamical triangulations to quantum gravity that describes our Universe - Yoshiyuki Watabiki

  3. [2212.13077] - Nonminimal Higgs Inflation and Initial Conditions in Cosmology - Andrei O. Barvinsky, Alexander Yu. Kamenshchik

Tue - 12/27/22

Loop quantum cosmological model from ADM Hamiltonian

  • Authors: You Ding, Xiangdong Zhang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2212.13159
  • Abstract The loop quantum cosmological model from ADM Hamiltonian is studied in this paper. We consider the spatially flat homogeneous FRW model. It turns out that the modified Friedmann equation keeps the same form as the APS LQC model. However, the critical matter density for the bounce point is only a quarter of the previous APS model, i.e. $\rho_{cL}=\frac{\rho_c}{4}$. This is interesting because the lower critical bounce density means the quantum gravity effects will get involved earlier than the previous LQC model. Besides, the lower critical density also means the detection of quantum gravity effects easier than the previous model.

An extension of the $\mathrm{U}!\left(1\right)$ BF theory, Turaev-Viro invariant and Drinfeld center construction. Part I: Quantum fields, quantum currents and Pontryagin duality

  • Authors: Emil Høssjer, Philippe Mathieu, Frank Thuillier
  • Subjects: Mathematical Physics (math-ph); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.12872
  • Abstract In this first of a series of articles dedicated to natural extensions of the U(1) BF theory, abelian Turaev-Viro (TV) construction and corresponding Drinfeld center construction for any closed oriented smooth manifolds, we present the mathematical background that will be used.

  1. [2212.13031] - Approximately stealth black hole in higher-order scalar-tensor theories - Antonio De Felice, Shinji Mukohyama, Kazufumi Takahashi

  2. [2212.13109] - The causality road from dynamical triangulations to quantum gravity that describes our Universe - Yoshiyuki Watabiki

  3. [2212.13077] - Nonminimal Higgs Inflation and Initial Conditions in Cosmology - Andrei O. Barvinsky, Alexander Yu. Kamenshchik

Mon - 12/26/22

Regularizations and quantum dynamics in loop quantum cosmology

  • Authors: Maciej Kowalczyk, Tomasz Pawłowski
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2212.12527
  • Abstract One of critical components of Loop Quantum Gravity (LQG) and Cosmology (LQC) – Thiemann regularization procedure is non-unique. Different choices of particular prescriptions lead to models which differ in both mathematical structure and physical predictions. Here we briefly recall a set of such prescriptions proposed in the literature in context of isotropic LQC on the example of a flat universe with massless scalar matter content. For the one least investigated so far, further called Yang-Ding-Ma prescription, a detailed analysis of its mathematical structure and resulting quantum dynamics is performed, confirming and extending the results obtained so far by phenomenological methods. In order to probe the dynamics, a relatively robust method (working in the approximation of the macroscopic universe) of evaluating quantum trajectories is devised. Said method is a variant of a semiclassical treatment that allows to express the trajectories analytically as function of internal clock and a set of certain central moments – constants of motion encoding quantum corrections up to arbitrary order in systematic manner. As a test of method’s robustness analogous evaluation of the quantum trajectory in volume is performed for those of other prescriptions, for which it is applicable. The limitations of the treatment are further briefly discussed.

There is no new related paper today

  1. [2212.12175] - Beyond the Born rule in quantum gravity - Antony Valentini

  2. [2212.12466] - Stochastic fluctuation in heart of time: A new window to quantum gravity - Behzad Tajahmad

  3. [2212.12342] - Perturbing the symmetric orbifold from the worldsheet - Marc-Antoine Fiset, Matthias R. Gaberdiel, Kiarash Naderi, Vit Sriprachyakul

New papers last week