Immirzi parameter without Immirzi ambiguity: Conformal loop quantization of scalar-tensor gravity

Olivier J. Veraguth; Charles H.-T. Wang

doi:10.1103/physrevd.96.084011

Loop quantization of spherically symmetric midi-superspaces : the interior problem

10.1063/1.2902798 ◽

2008 ◽

Cited By ~ 44

Author(s):

Miguel Campiglia ◽

Rodolfo Gambini ◽

Jorge Pullin ◽

Alfredo Macias ◽

Claus Lämmerzahl ◽

...

Keyword(s):

Spherically Symmetric ◽

Interior Problem ◽

Loop Quantization

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Polymer quantum effects on compact stars models

International Journal of Modern Physics D ◽

10.1142/s0218271815500339 ◽

2015 ◽

Vol 24 (05) ◽

pp. 1550033 ◽

Cited By ~ 8

Author(s):

Guillermo Chacón-Acosta ◽

Héctor H. Hernandez-Hernandez

Keyword(s):

Semiclassical Approximation ◽

Generalized Uncertainty Principle ◽

Compact Object ◽

Compact Stars ◽

One Dimensional ◽

Degenerate Fermi Gas ◽

Mechanical Models ◽

Degeneracy Pressure ◽

Loop Quantization ◽

Bose Einstein

In this work we study a completely degenerate Fermi gas at zero temperature by a semiclassical approximation for a Hamiltonian that arises in polymer quantum mechanics. Polymer quantum systems are quantum mechanical models quantized in a similar way as in loop quantum gravity, allowing the study of the discreteness of space and other features of the loop quantization in a simplified way. We obtain the polymer modified thermodynamical properties for this system by noticing that the corresponding Fermi energy is exactly the same as if one directly polymerizes the momentum pF. We also obtain the expansion of the corresponding thermodynamical variables in terms of small values of the polymer length scale λ. We apply these results to study a simple model of a compact one-dimensional star where the gravitational collapse is supported by electron degeneracy pressure. As a consequence, polymer corrections to the mass of the object are found. By using bounds for the polymer length found in Bose–Einstein condensates experiments we compute the modification in the mass of the compact object due to polymer effects of order ~ 10-8. This result is similar to the other order found by different approaches such as generalized uncertainty principle (GUP), and that certainly is within the error reported in typical measurements of white dwarf masses.

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Is classical flat Kasner spacetime flat in quantum gravity?

International Journal of Modern Physics D ◽

10.1142/s0218271816420013 ◽

2016 ◽

Vol 25 (08) ◽

pp. 1642001 ◽

Cited By ~ 12

Author(s):

Parampreet Singh

Keyword(s):

Quantum Gravity ◽

Minkowski Spacetime ◽

Quantum Geometry ◽

Classical Level ◽

Bianchi I ◽

Spacetime Curvature ◽

Loop Quantization ◽

Universal Bounds ◽

Vacuum Spacetime ◽

Geometric Effects

Quantum nature of classical flat Kasner spacetime is studied using effective spacetime description in loop quantum cosmology (LQC). We find that even though the spacetime curvature vanishes at the classical level, nontrivial quantum gravitational effects can arise. For the standard loop quantization of Bianchi-I spacetime, which uniquely yields universal bounds on expansion and shear scalars and results in a generic resolution of strong singularities, we find that a flat Kasner metric is not a physical solution of the effective spacetime description, except in a limit. The lack of a flat Kasner metric at the quantum level results from a novel feature of the loop quantum Bianchi-I spacetime: quantum geometry induces nonvanishing spacetime curvature components, making it not Ricci flat even when no matter is present. The noncurvature singularity of the classical flat Kasner spacetime is avoided, and the effective spacetime transits from a flat Kasner spacetime in asymptotic future, to a Minkowski spacetime in asymptotic past. Interestingly, for an alternate loop quantization which does not share some of the fine features of the standard quantization, flat Kasner spacetime with expected classical features exists. In this case, even with nontrivial quantum geometric effects, the spacetime curvature vanishes. These examples show that the character of even a flat classical vacuum spacetime can alter in a fundamental way in quantum gravity and is sensitive to the quantization procedure.

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