Sun - 11/13/22

Quantum geometry and black holes

  • Authors: Rodolfo Gambini, Javier Olmedo, Jorge Pullin
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.05621
  • Abstract We summarize our work on spherically symmetric midi-superspaces in loop quantum gravity. Our approach is based on using inhomogeneous slicings that may penetrate the horizon in case there is one and on a redefinition of the constraints so the Hamiltonian has an Abelian algebra with itself. We discuss basic and improved quantizations as is done in loop quantum cosmology. We discuss the use of parameterized Dirac observables to define operators associated with kinematical variables in the physical space of states, as a first step to introduce an operator associated with the space-time metric. We analyze the elimination of singularities and how they are replaced by extensions of the space-times. We discuss the charged case and potential observational consequences in quasinormal modes. We also analyze the covariance of the approach. Finally, we comment on other recent approaches of quantum black holes, including mini-superspaces motivated by loop quantum gravity.

There is no new related paper today

  1. [2211.05508] - Scaling solutions for asymptotically free quantum gravity - Saswato Sen, Christof Wetterich, Masatoshi Yamada

  2. [2211.05606] - Classical and quantum nonlocal gravity - Arnau Bas i Beneito, Gianluca Calcagni, Lesław Rachwał

Sat - 11/12/22

Quantum geometry and black holes

  • Authors: Rodolfo Gambini, Javier Olmedo, Jorge Pullin
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.05621
  • Abstract We summarize our work on spherically symmetric midi-superspaces in loop quantum gravity. Our approach is based on using inhomogeneous slicings that may penetrate the horizon in case there is one and on a redefinition of the constraints so the Hamiltonian has an Abelian algebra with itself. We discuss basic and improved quantizations as is done in loop quantum cosmology. We discuss the use of parameterized Dirac observables to define operators associated with kinematical variables in the physical space of states, as a first step to introduce an operator associated with the space-time metric. We analyze the elimination of singularities and how they are replaced by extensions of the space-times. We discuss the charged case and potential observational consequences in quasinormal modes. We also analyze the covariance of the approach. Finally, we comment on other recent approaches of quantum black holes, including mini-superspaces motivated by loop quantum gravity.

There is no new related paper today

  1. [2211.05508] - Scaling solutions for asymptotically free quantum gravity - Saswato Sen, Christof Wetterich, Masatoshi Yamada

  2. [2211.05606] - Classical and quantum nonlocal gravity - Arnau Bas i Beneito, Gianluca Calcagni, Lesław Rachwał

Fri - 11/11/22

Quantum geometry and black holes

  • Authors: Rodolfo Gambini, Javier Olmedo, Jorge Pullin
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.05621
  • Abstract We summarize our work on spherically symmetric midi-superspaces in loop quantum gravity. Our approach is based on using inhomogeneous slicings that may penetrate the horizon in case there is one and on a redefinition of the constraints so the Hamiltonian has an Abelian algebra with itself. We discuss basic and improved quantizations as is done in loop quantum cosmology. We discuss the use of parameterized Dirac observables to define operators associated with kinematical variables in the physical space of states, as a first step to introduce an operator associated with the space-time metric. We analyze the elimination of singularities and how they are replaced by extensions of the space-times. We discuss the charged case and potential observational consequences in quasinormal modes. We also analyze the covariance of the approach. Finally, we comment on other recent approaches of quantum black holes, including mini-superspaces motivated by loop quantum gravity.

There is no new related paper today

  1. [2211.05508] - Scaling solutions for asymptotically free quantum gravity - Saswato Sen, Christof Wetterich, Masatoshi Yamada

  2. [2211.05606] - Classical and quantum nonlocal gravity - Arnau Bas i Beneito, Gianluca Calcagni, Lesław Rachwał

Thu - 11/10/22

Gauge-invariant perturbations at a quantum gravity bounce

  • Authors: Steffen Gielen, Lisa Mickel
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2211.04500
  • Abstract We study the dynamics of gauge-invariant scalar perturbations in cosmological scenarios with a modified Friedmann equation, such as quantum gravity bouncing cosmologies. We work within a separate universe approximation which captures wavelengths larger than the cosmological horizon; this approximation has been successfully applied to loop quantum cosmology and group field theory. We consider two variables commonly used to characterise scalar perturbations: the curvature perturbation on uniform-density hypersurfaces $\zeta$ and the comoving curvature perturbation $\mathcal{R}$. For standard cosmological models in general relativity as well as in loop quantum cosmology, these quantities are conserved and equal on super-horizon scales for adiabatic perturbations. Here we show that while these statements can be extended to a more general form of modified Friedmann equations similar to that of loop quantum cosmology, in other cases, such as the simplest group field theory bounce scenario, $\zeta$ is conserved across the bounce whereas $\mathcal{R}$ is not. We relate our results to approaches based on a second order equation for a single perturbation variable, such as the Mukhanov-Sasaki equation.

Scalar curvature operator for quantum-reduced loop gravity

  • Authors: Jerzy Lewandowski, Ilkka Mäkinen
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.04826
  • Abstract In a previous article we have introduced an operator representing the three-dimensional scalar curvature in loop quantum gravity. In this article we examine the new curvature operator in the setting of quantum-reduced loop gravity. We derive the explicit form of the curvature operator as an operator on the Hilbert space of the quantum-reduced model. As a simple practical example, we study the expectation values of the operator with respect to basis states of the reduced Hilbert space.

Geometry from local flatness in Lorentzian spin foam theories

  • Authors: Pietro Dona
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2211.04743
  • Abstract Local flatness is a property shared by all the spin foam models. It ensures that the theory’s fundamental building blocks are flat by requiring locally trivial parallel transport. In the context of simplicial Lorentzian spin foam theory, we show that local flatness is the main responsible for the emergence of geometry independently of the details of the spin foam model. We discuss the asymptotic analysis of the EPRL spin foam amplitudes in the large quantum number regime, highlighting the interplay with local flatness.

Wed - 11/09/22

Loop quantum black hole in a gravitational collapse model

  • Authors: Jinsong Yang, Cong Zhang, Yongge Ma
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.04263
  • Abstract The gravitational collapse plays an important role in the formation of black holes as well as for our understanding of the spacetime structure. In this paper, we propose the exterior effective spacetime that are well matched to the interior effective model of loop quantum cosmology for the Datt-Oppenheimer-Snyder gravitational collapse model. The analysis shows that, as the collapse goes on, the quantum-corrected black hole can form with the occurrence of horizon. The quantum gravitational effects will stop the collapse of the dust matter when the energy density reaches the Planck scale and bounce it to an expanding phase, resulting in the resolution of the singularity of the classical black hole. Moreover, the quantum gravitational corrections can affect the black hole shadows by their sizes. The stability of the quantum-corrected black hole under perturbations is also studied by calculating the quasinormal modes. It turns out that the quantum-corrected black hole is stable against the scalar and vector perturbations.

Bouncing Universe in Loop Quantum Gravity: full theory calculation

  • Authors: Marcin Kisielowski
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.04440
  • Abstract In Loop Quantum Gravity mathematically rigorous models of full quantum gravity were proposed. In this paper we study a cosmological sector of one of the models describing quantum gravity with positive cosmological constant coupled to massless scalar field. In our previous research we introduced a method to reduce the model to homogeneous-isotropic sector at the quantum level. In this paper we propose a method to restrict to the spatially flat sector. After this restriction the number of degrees of freedom gets substantially reduced. This allows us to make numerical calculations. Remarkably, the resulting model shares some structural similarities with the Loop Quantum Cosmological models and therefore sheds some new light on the relation between Loop Quantum Gravity and Loop Quantum Cosmology. According to our model the evolution of the Universe is periodic. The quantum gravity effects resolve the Big Bang singularity leading to a Big Bounce and cause the Universe to contract after a classical expansion phase (Big Crunch).

There is no new related paper today

  1. [2211.03806] - Integrability treatment of AdS/CFT orbifolds - Torben Skrzypek

Tue - 11/08/22

Modified cosmology from the thermodynamics of apparent horizon

  • Authors: Shin’ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2211.02822
  • Abstract In the realm of the Bekenstein-Hawking entropy, the thermodynamics of apparent horizon bridges with the usual FLRW (Friedmann-Lema\^{i}tre-Robertson-Walker) equation only for a special case where the matter field is given by a perfect fluid having equation of state (EoS) parameter $= -1$, i.e $p = -\rho$ with $\rho$ and $p$ represent the energy density and the pressure of the fluid, respectively. To include the case $p \neq -\rho$, we consider the modification of the Bekenstein-Hawking entropy in the present work. In particular, we develop an entropy function that leads to the usual FLRW equations, for a $general$ EoS of the matter fluid given by $p = w\rho$, directly from the thermodynamics of the apparent horizon. The newly developed entropy acquires a correction over the Bekenstein-Hawking entropy and differs from the known entropies like the Tsallis, R'{e}nyi, Barrow, Sharma-Mittal, Kaniadakis, and Loop Quantum Gravity entropies proposed so far. Based on this finding, we examine how the Friedmann equations of the apparent horizon cosmology are accordingly modified if one starts with a general entropy depending on the Bekenstein-Hawking entropy. This results in some interesting cosmological consequences during the early and late stages of the universe.

There is no new related paper today

  1. [2211.03596] - Quantum gravity and scale symmetry in cosmology - C. Wetterich

  2. [2211.03609] - Bouncing cosmology in modified gravity with higher-order Gauss-Bonnet curvature term - Santosh V Lohakare, Francisco Tello-Ortiz, S.K. Tripathy, B. Mishra

Mon - 11/07/22

There is no new related paper today

There is no new related paper today

  1. [2211.02055] - Shift Symmetries and AdS/CFT - Erin Blauvelt, Laura Engelbrecht, Kurt Hinterbichler

  2. [2211.02064] - Universal Gibbons-Hawking-York term for theories with curvature, torsion and non-metricity - Johanna Erdmenger, Bastian Heß, Ioannis Matthaiakakis, René Meyer

  3. [2211.02345] - On-Shell Action for Type IIB Supergravity and Superstrings on $AdS_5 \times S^5$ - Subhroneel Chakrabarti, Divyanshu Gupta, Arkajyoti Manna

New papers last week