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.
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Notes
- 1.
For the conceptual framework underlying effective equations see, e.g., Section V of [9]. Note that the term ‘effective equations’ has a very different connotation here than in standard quantum field theory. This has caused occasional confusion in the literature. In LQG one does not integrate out ‘high energy modes’; Planck scale effects are retained. In LQC, for example, there are states that remain sharply peaked even in the Planck regime and the effective equations capture the evolution of the peak of the quantum wave function in these states, ignoring the fluctuations.
- 2.
Because the spatial curvature features on the right side of Einstein’s evolution equations, the quantum corrected version of the classical dynamical trajectories (7.3) and (7.4) along which \(\delta _b\) and \(\delta _c\) are to remain constant themselves feature \(\delta _b\) and \(\delta _c\) (see (7.9), (7.10) and (7.11)). Therefore the issue of finding \(\delta _b\) and \(\delta _c\) that are Dirac observables is rather subtle conceptually and quite intricate technically. These subtleties has led to some concerns [31]. This issue is analyzed in detail [35,36,37, 44]. Consistency of the final results directly follows from the effective equations (7.6)–(7.8).
- 3.
This strategy of using time-like 3-manifolds to specify fields and then ‘evolving’ them in space-like directions was proposed and pursued in [39] for the Hamiltonian framework of full LQG. As discussed there, in the full theory one encounters certain non-trivial technical difficulties associated with the fact that SU(1,1) is non-compact. These issues do not arise in the homogeneous context discussed here.
- 4.
In this review, we did not touch on the issue of black hole entropy that arises in LQG by counting microstates of the area operator that are compatible with parameters characterizing a given macroscopic black hole (see. e.g., [139]. The possibility of testing discreteness of area using gravitational waves has drawn considerable attention in the literature. It has been argued that the simplest area spectrum with area eigenvalues given by \(k n\, \ell _\textrm{Pl}^2\) (where n is an integer and k a constant), considered by Bekenstein and Mukhanov [140], could be ruled out using data from a sufficiently large number of compact binary mergers. But in LQG the area spectrum is not equidistant, it crowds exponentially, making the continuum an excellent approximation very quickly. However, for small black holes the area eigenvalues are grouped, exhibiting a band structure, and the separation between bands is \({O}(\ell _\textrm{Pl}^2)\). If this structure were to persist for large rotating black holes, each band would serve as a proxy of the Bekenstein-Mukhanov eigenvalues and gravitational observations would then lead to non-trivial constraints [141]. However, currently there is no evidence that points to the persistence of bands for macroscopic areas.
References
N. Englehardt, G.T. Horowitz, Int. J. Mod. Phys. D 25, 1643002 (2016)
S.W. Hawking, [erratum: Commun. Math. Phys. 46, 206 (1976)]. https://doi.org/10.1007/BF02345020
S.W. Hawking, M.J. Perry, A. Strominger 116, 231301 (2016)
W.G. Unruh, R.M. Wald, Information loss. Rep. Prog. Phys. 80, 092002 (2017)
A. Almheiri, D. Marolf, J. Polchinski, D. Stanford, J. Sully, JHEP 09, 018 (2013)
S. Giddings, Phys. Lett. B 738, 92 (2014)
D. Marolf, Rep. Prog. Phys. 80, 092001 (2017)
A. Ashtekar, J. Pullin (eds.), Loop Quantum Gravity: The First 30 Years (World Scientific, Singapore, 2017)
A. Ashtekar, P. Singh, Class. Quantum Gravity 28, 213001 (2011)
P. Singh, Class. Quantum Gravity 26, 125005 (2009)
I. Agullo, P. Singh, in Loop Quantum Gravity: The First 30 Years, ed. by A. Ashtekar, J. Pullin (World Scientific, Singapore, 2017). arXiv: 1612.01236
A. Ashtekar, M. Bojowald, Class. Quantum Gravity 23, 391 (2006)
L. Modesto, Class. Quantum Gravity 23, 5587 (2006)
M. Campiglia, R. Gambini, J. Pullin, AIP Conf. Proc. 977, 52–63 (2008)
R. Gambini, J. Pullin, Phys. Rev. Lett. 110, 211301 (2013)
D. Cartin, G. Khanna, Phys. Rev. D 73, 104009 (2006)
C.G. Boehmer, K. Vandersloot, Phys. Rev. D 76, 1004030 (2007)
D.W. Chiou, Phys. Rev. D 78, 064040 (2008)
A. Corichi, P. Singh, Class. Quantum Gravity 33, 055006 (2016)
J. Olmedo, S. Saini, P. Singh, Class. Quantum Gravity 34, 225011 (2017)
J. Cortez, W. Cuervo, H.A. Morales-Técotl, J.C. Ruelas, Phys. Rev. D 95, 064041 (2017)
A. Yonika, G. Khanna, P. Singh, Class. Quantum Gravity 35, 045007 (2018)
A. Joe, P. Singh, Class. Quantum Gravity 32, 015009 (2015)
D.-W. Chiou, Phys. Rev. D 78, 044019 (2008)
J. Brannlund, S. Kloster, A. DeBenedictis, Phys. Rev. D 79, 084023 (2009)
R. Gambini, J. Olmedo, J. Pullin, Class. Quantum Gravity 31, 095009 (2014)
N. Dadhich, A. Joe, P. Singh, Class. Quantum Gravity 32, 185006 (2015)
A. Ashtekar, J. Olmedo, P. Singh, Phys. Rev. Lett. 121, 241301 (2018)
A. Ashtekar, J. Olmedo, P. Singh, Phys. Rev. D 98, 126003 (2018)
A. Ashtekar, J. Olmedo, Int. J. Mod. Phys. 29, 2050076 (2020)
N. Bodendorfer, F.M. Mele, J. Münch, Class. Quantum Gravity 36, 187001 (2019)
C. Zhang, Y. Ma, S. Song, X. Zhang, Phys. Rev. Phys. Rev. D 105, 024069 (2020)
R. Gambini, J. Olmedo, J. Pullin, Front. Astron. Space Sci. 8, 74 (2021)
C. Zhang, Y. Ma, S. Song, X. Zhang, Phys. Rev. D 105, 024069 (2022)
B.E. Navascués, A. García-Quismondo, G.A. Mena Marugán, Phys. Rev. D 106, 063516 (2022)
A. García-Quismondo, G. A. Mena Marugán, Phys. Rev. D 106, 023532 (2022)
B. E. Navascués, A. García-Quismondo, G. A. Mena Marugán, Phys. Rev. D106, 043531 (2022)
M. Han, H. Liu. arXiv:2212.04605
H. Liu, K. Noui, Class. Quantum Gravity 34, 135008 (2017)
A. Ashtekar, M. Bojowald, Class. Quantum Gravity 22, 3349 (2005)
A. Ashtekar, B. Krishnan, Phys. Rev. D 68, 104030 (2003)
A. Ashtekar, B. Krishnan, Liv. Rev. (Relativ.) 7(10) (2004)
I. Booth, Can. J. Phys. 83, 1073 (2005)
G. Ongole, H. Zhang, T. Zhu, A. Wang, B. Wang, Universe 8, 543 (2022)
A. Ashtekar, T. Pawlowski, P. Singh, Phys. Rev. D 74, 084003 (2006)
A. Ashtekar, M. Bojowald, J. Lewandowski, Adv. Theo. Math. Phys. 7, 233–268 (2003)
J. Willis, On the low energy ramifications and a mathematical extension of loop quantum gravity; Ph.D. Dissertation, The Pennsylvaina State University (2004)
V. Taveras, Phys. Rev. D 78, 064072 (2008)
G.W. Gibbons, M.J. Perry, Proc. Roy. Soc. Lond. A 358, 467 (1978)
S.A. Fulling, S.N.M. Ruijsenaars, Phys. Rep. 152, 135 (1987)
T. Levi-Civita, Il sottocaso B2: soluzioni oblique, Atti. Accad. Naz. Lincei Cl. Sci. Fis. Mat. Nat. Rend. 27, 343 (1918)
W. Kinnersley, M. Walker, Phys. Rev. D 2, 1359 (1970)
A. Ashtekar, T. Dray, Commun. Math. Phys. 79, 581 (1981)
M. Bouhmadi-López, S. Brahma, C.-Y. Chen, P. Chen, D.-H. Chen, Phys. Dark Univ. 30, 100701 (2020)
A. Ashtekar, A. Magnon, J. Math. Phys. 25, 2682 (1984)
R. Schoen, Localizing solutions of the Einstein equations, Lectures at the Institut Henri Poincaré, General Relativity: A Celebration of the 100th Anniversary (2015). https://philippelefloch.files.wordpress.com/2015/11/2015-ihp-richardschoen.pdf
T. Thiemann, Class. Quantum Gravity 12, 181 (2003)
M. Bojowald, R. Swiderski, Class. Quantum Gravity 23, 2129 (2006)
D.-W. Chiou, W.-T. Ni, A. Tang. arXiv:1212.1265
J. Ben Achour, F. Lamy, H. Liu, K. Noui, Euro. Phys. Lett. 123, 20006 (2018)
J.G. Kelly, R. Santacruz, E. Wilson-Ewing, Phys. Rev. D 102, 106024 (2020)
J.G. Kelly, R. Santacruz, E. Wilson-Ewing, Class. Quant. Grav. 38, 04LT01 (2021)
R. Gambini, J. Olmedo, J. Pullin, Class. Quantum Gravity 37, 205012 (2020)
M. Han, H. Liu, Class. Quantum Gravity 39, 035011 (2022)
V. Husain, J.G. Kelly, R. Santacruz, E. Wilson-Ewing, Phys. Rev. Lett. 128, 121301 (2021)
C. Zhang, Phys. Rev. D 104, 126003 (2021)
V. Husain, J.G. Kelly, R. Santacruz, E. Wilson-Ewing, Phys. Rev. D 106, 024014 (2022)
K. Giesel, M. Han, B. Li, H. Liu, P. Singh, Phys. Rev. D 107, 044047 (2023)
L. Modesto, Int. J. Theor. Phys. 47, 357 (2008)
S. Hossenfelder, L. Modesto, I. Premont-Schwarz, Phys. Rev. D 81, 044036 (2010)
Y. Tavakoli, J. Marto, A. Dapor, Int. J. Mod. Phys. D 23, 1450061 (2014)
C. Bambi, D. Malafarina, L. Modesto, Phys. Rev. D 88, 044009 (2013)
Y. Liu, D. Malafarina, L. Modesto, C. Bambi, Phys. Rev. D 90, 044040 (2014)
J. Ben Achour, S. Brahma, J.-P. Uzan, JCAP 2003, 041 (2020)
B.F. Li, P. Singh, Universe 7(11), 406 (2021)
A. Corichi, P. Singh, Phys. Rev. D 78, 024034 (2008)
P. Hájíček, Quantum Gravity: Quantum Theory of Gravitational Collapse. Lecture Notes on Quantum Conchology, Springer Berlin Heidelberg, pp. 255–299 (2003)
M. Campiglia, R. Gambini, J. Olmedo, J. Pullin, Class. Quantum Gravity33, LT01 (2016)
J. Ziprick, J. Gegenberg, G. Kunstatter, Phys. Rev. D 94, 104076 (2016)
K. Giesel, B.-F. Li, P. Singh, Phys. Rev. D 104, 106017 (2021)
M. Bojowald, T. Harada, R. Tibrewala, Phys. Rev. D 78, 064057 (2008)
M. Bojowald, J.D. Reyes, R. Tibrewala, Phys. Rev. D 80, 084002 (2009)
A. Alonso-Bardaji, D. Brizuela, Phys. Rev. D 104, 084064 (2021)
A. Alonso-Bardaji, D. Brizuela, R. Vera, Phys. Lett. B 829, 137075 (2022)
M.W. Choptuik, Phys. Rev. Lett. 70, 9 (1993)
V. Husain, O. Winkler, Class. Quantum Gravity 22, L127 (2005)
V. Husain. arXiv:0808.0949
J. Ziprick, G. Kunstatter, Phys. Rev. D 80, 024032 (2009)
A. Kreienbuehl, V. Husain, S.S. Seahra, Class. Quantum Gravity 29, 095008 (2012)
F. Benitez, R. Gambini, L. Lehner, S. Liebling, J. Pullin, Phys. Rev. Lett. 124, 071301 (2020)
F. Benitez, R. Gambini, S. Liebling, J. Pullin, Phys. Rev. D 104, 024008 (2021)
F. Benitez, R. Gambini, J. Pullin, Universe 8, 10 (2022)
C. Barceló, R. Carballo-Rubio, L.J. Garay, Int. J. Mod. Phys. D 23, 1442022 (2014)
C. Barcelo, R. Carballo-Rubio, L.J. Garay, G. Jannes, Class. Quantum Gravity 32, 035012 (2015)
C. Barceló, R. Carballo-Rubio, L.J. Garay, JHEP 01, 157 (2016)
R. Carballo-Rubio, F. Di Filippo, S. Liberati, M. Visser, Class. Quantum Gravity 37, 14 (2020)
K. Giesel, B.F. Li, P. Singh, S.A. Weigl, Phys. Rev. D 105, 066023 (2022)
S. Hod, T. Piran, Phys. Rev. D 55, 440 (1997)
T. Thiemann, Class. Quantum Gravity 15, 839 (1998)
A. Ashtekar, J. Lewandowski, H. Sahlmann, Class. Quantum Gravity 20, L11 (2003)
M. Bojowald, R. Goswami, R. Maartens, P. Singh, Phys. Rev. Lett. 95, 091302 (2005)
K. Vandersloot, Phys. Rev. D 75, 023523 (2007)
P. Singh, E. Wilson-Ewing, Class. Quantum Gravity 31, 035010 (2014)
T. Schmitz, Phys. Rev. D 101, 026016 (2020)
R.J. LeVeque, Finite Volume Methods for Hyperbolic Problems (Cambridge University Press, Cambridge, 2002)
C. Vaz, L. Witten, Gen. Rel. Gravity 43, 3429 (2011)
C. Kiefer, T. Schmitz, Phys. Rev. D 99, 126010 (2019)
W. Piechocki, T. Schmitz, Phys. Rev. D 102, 046004 (2020)
T. Schmitz, Phys. Rev. D 103, 064074 (2021)
J. Münch, Class. Quantum Gravity 38, 175015 (2021)
J. Ben Achour, S. Brahma, S. Mukohyama, J.P. Uzan, JCAP 09, 020 (2020)
S.W. Hawking, Phys. Rev. D 14, 2460 (1976)
P. Hajicek, Phys. Rev. D 36, 1066 (1987)
A. Ashtekar, The issue of information loss: the current status, ILQG seminar of February 23rd (2015). http://relativity.phys.lsu.edu/ilqgs/ashtekar022316.pdf
A. Ashtekar, Universe 6, 21 (2020)
S. Hayward, arXiv:gr-qc/0504038
S. Hayward, arXiv:gr-qc/0504037
D. Page, Phys. Rev. Lett. 71, 3743–3746 (1993)
M. Christodoulou, T. De Lorenzo, Phys. Rev. D 94, 104002 (2016)
M. Christodoulou, C. Rovelli, Phys. Rev. D 91, 064046 (2015)
A. Ashtekar, V. Taveras, M. Varadarajan, Phys. Rev. Lett. 100, 211302 (2008)
S.A. Hayward, Phys. Rev. Lett. 96, 031103 (2006)
V.P. Frolov, JHEP 1405, 049 (2014)
J.M. Bardeen, arXiv:1406.4098
C. Rovelli, F. Vidotto, Int. J. Mod. Phys. D 23, 1442026 (2014)
E. Bianchi, M. Smerlak, Gen. Relativ. Gravit. 46, 1809 (2014)
E. Bianchi, T. De Lorenzo, M. Smerlak, JHEP 06, 180 (2015)
H.M. Haggard, C. Rovelli, Phys. Rev. D 92, 104020 (2015)
M. Christodoulou, Geometry transition in covariant LQG: black to white. http://relativity.phys.lsu.edu/ilqgs/christodoulou102417.pdf
E. Bianchi, M. Christodoulou, F. D’Ambrosio, H. M Haggard, C. Rovelli, Class. Quantum Grav. 35, 225003 (2018)
P. Martin-Dessuad, C. Rovelli, Class. Quantum Gravity 36, 245002 (2019)
A. Ori, Personal communication
I. Agullo, A. Ashtekar, W. Nelson, Class. Quantum Gravity 30, 085014 (2013)
L. Amadei, A. Perez, Phys. Rev. D 106, 063528 (2022)
P. Diener, B. Gupt, P. Singh, Class. Quantum Gravity 31, 105015 (2014)
P. Diener, A. Joe, M. Megevand, P. Singh, Class. Quantum Gravity 34, 094004 (2017)
V. Faraoni, A. Giusti, Symmetry 12, 1264 (2020)
M. Bojowald, Universe 6, 125 (2020)
A. Perez, Rept. Prog. Phys. 80, 126901 (2017)
J.D. Bekenstein, V.F. Mukhanov, Phys. Lett. B 360, 7–12 (1995)
I. Agullo, V. Cardoso, A. del Rio, M. Maggiore, J. Pullin Phys. Rev. Lett. 126, 041302 (2021)
R.G. Daghigh, M.D. Green, G. Kunstatter, Phys. Rev. D 103, 084031 (2021)
D. del-Corral, J. Olmedo, Phys. Rev. D 105, 064053 (2022)
M. Bojowald. arXiv: 1906.04650
G. Olmo, P. Singh, JCAP 0901, 030 (2009)
R. Dijkgraaf, H. Verlinde, E. Verlinde, Null. Phys. B 371, 269–314 (2002)
D. Grumiller, JHEP 0211, 018 (2002)
D. Grumiller, JHEP 0505, 028 (2005)
A. Ashtekar, F. Pretorius, F. Ramazanoglu, Phys. Rev. D 83, 044040 (2011)
A. Ori, Gen. Relativ. Gravit. 48, 9 (2016)
W.C. Gan, G. Ongole, E. Alesci, Y. An, F.W. Shu, A. Wang, Phys. Rev. D. 106, 126013 (2022)
M. Assanioussi, A. Dapor, K. Liegener, Phys. Rev. D 101, 026002 (2020)
Acknowledgements
This work was supported in part by the NSF grant PHY-1806356, PHY-1912274 and PHY-2110207, Penn State research funds associated with the Eberly Chair and Atherton professorship, and by Projects PID2020-118159GB-C43, PID2019-105943GB-I00 (with FEDER contribution), by the Spanish Government, and also by the “Operative Program FEDER2014-2020 Junta de Andalucía-Consejería de Economía y Conocimiento” under project E-FQM-262-UGR18 by Universidad de Granada. We would like to thank Eugenio Bianchi, Kristina Giesel, Muxin Han, Bao-Fei Li, Guillermo Mena, Sahil Saini and Ed Wilson-Ewing for discussions, and Tommaso De Lorenzo for Figures 4–6.
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Ashtekar, A., Olmedo, J., Singh, P. (2023). Regular Black Holes from Loop Quantum Gravity. In: Bambi, C. (eds) Regular Black Holes. Springer Series in Astrophysics and Cosmology. Springer, Singapore. https://doi.org/10.1007/978-981-99-1596-5_7
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