Fri - 12/31/21

On consistent gauge fixing conditions in polymerized gravitational systems

  • Authors: Kristina Giesel, Bao-Fei Li, Parampreet Singh, Stefan Andreas Weigl
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2112.13860
  • Abstract For classical gravitational systems the lapse function and the shift vector are usually determined by imposing appropriate gauge fixing conditions and then demanding their preservation with respect to the dynamics generated by a canonical Hamiltonian. Effective descriptions encoding quantum geometric effects motivated by loop quantum gravity for symmetry reduced models are often captured by polymerization of connection (or related) variables in gauge fixing conditions as well as constraints. Usually, one chooses the same form of polymerization in both cases. A pertinent question is if the dynamical stability of the effective gauge fixing conditions under the effective dynamics generated by the polymerized canonical Hamiltonian is provided by the lapse function and the shift vector obtained from the polymerization of their classical counterparts. If this is the case, then we say that gauge fixing and polymerization commute. In this manuscript we investigate these issues and obtain consistency conditions for the commutativity of gauge fixing and polymerization. Our analysis shows that such a commutativity occurs in rather special situations and reveals pitfalls in making seemingly well motivated choices which turn out to be inconsistent with the effective dynamics. We illustrate these findings via examples of symmetry reduced models in the loop quantization of the Schwarzschild interior and Lema\^{\i}tre-Tolman-Bondi (LTB) spacetimes and report the non-commutativity of gauge fixing and polymerization, and inherent limitations of some choices made in the literature with a consistent effective dynamics.

There is no new related paper today

  1. [2112.14730] - Quantum Gravity Corrections to the Fall of the Apple - Samarth Chawla, Maulik Parikh

  2. [2112.14593] - Chaos by Magic - Kanato Goto, Tomoki Nosaka, Masahiro Nozaki

Thu - 12/30/21

On consistent gauge fixing conditions in polymerized gravitational systems

  • Authors: Kristina Giesel, Bao-Fei Li, Parampreet Singh, Stefan Andreas Weigl
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2112.13860
  • Abstract For classical gravitational systems the lapse function and the shift vector are usually determined by imposing appropriate gauge fixing conditions and then demanding their preservation with respect to the dynamics generated by a canonical Hamiltonian. Effective descriptions encoding quantum geometric effects motivated by loop quantum gravity for symmetry reduced models are often captured by polymerization of connection (or related) variables in gauge fixing conditions as well as constraints. Usually, one chooses the same form of polymerization in both cases. A pertinent question is if the dynamical stability of the effective gauge fixing conditions under the effective dynamics generated by the polymerized canonical Hamiltonian is provided by the lapse function and the shift vector obtained from the polymerization of their classical counterparts. If this is the case, then we say that gauge fixing and polymerization commute. In this manuscript we investigate these issues and obtain consistency conditions for the commutativity of gauge fixing and polymerization. Our analysis shows that such a commutativity occurs in rather special situations and reveals pitfalls in making seemingly well motivated choices which turn out to be inconsistent with the effective dynamics. We illustrate these findings via examples of symmetry reduced models in the loop quantization of the Schwarzschild interior and Lema\^{\i}tre-Tolman-Bondi (LTB) spacetimes and report the non-commutativity of gauge fixing and polymerization, and inherent limitations of some choices made in the literature with a consistent effective dynamics.

There is no new related paper today

  1. [2112.14730] - Quantum Gravity Corrections to the Fall of the Apple - Samarth Chawla, Maulik Parikh

  2. [2112.14593] - Chaos by Magic - Kanato Goto, Tomoki Nosaka, Masahiro Nozaki

Wed - 12/29/21

There is no new related paper today

On the discrete version of the Reissner-Nordström solution

  • Authors: V.M. Khatsymovsky
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2112.13823
  • Abstract This paper generalizes our previous paper on the discrete Schwarzschild type solution in the Regge calculus, the simplicial electrodynamics earlier considered in the literature is incorporated in the case of the presence of a charge. Validity of the path integral approach is assumed, of which the only consequence used here is a loose fixation of edge lengths around a finite nonzero scale (we have considered the latter earlier). In essence, the problem of determining the optimal background metric and electromagnetic field for the perturbative expansion generated by the functional integral is considered, for which the skeleton Regge and electrodynamic equations are analyzed. For the Regge equations, as we have earlier found, the Regge action on the simplest periodic simplicial structure and in the leading order over metric variations between 4-simplices can be substituted by a finite-difference form of the Hilbert-Einstein action (the piecewise constant metric there is defined by providing the vertices with coordinates). Thus we get the absence of the singularity inherent in the continuous solution. At the same time, the discrete solution is close to the continuum Reissner-Nordstr"om one at large distances.

  1. [2112.12861] - Quantum geodesics on $λ$-Minkowski spacetime - Chengcheng Liu, Shahn Majid

  2. [2112.13103] - Galaxy rotation curves in multi-fractional spacetimes - Gianluca Calcagni, Gabriele U. Varieschi

  3. [2112.13216] - Quantum gravity corrections to the matter dynamics in the presence of a reference fluid - Giulia Maniccia, Giovanni Montani

  4. [2112.12828] - Gravity and the Crossed Product - Edward Witten

Tue - 12/28/21

There is no new related paper today

On the discrete version of the Reissner-Nordström solution

  • Authors: V.M. Khatsymovsky
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2112.13823
  • Abstract This paper generalizes our previous paper on the discrete Schwarzschild type solution in the Regge calculus, the simplicial electrodynamics earlier considered in the literature is incorporated in the case of the presence of a charge. Validity of the path integral approach is assumed, of which the only consequence used here is a loose fixation of edge lengths around a finite nonzero scale (we have considered the latter earlier). In essence, the problem of determining the optimal background metric and electromagnetic field for the perturbative expansion generated by the functional integral is considered, for which the skeleton Regge and electrodynamic equations are analyzed. For the Regge equations, as we have earlier found, the Regge action on the simplest periodic simplicial structure and in the leading order over metric variations between 4-simplices can be substituted by a finite-difference form of the Hilbert-Einstein action (the piecewise constant metric there is defined by providing the vertices with coordinates). Thus we get the absence of the singularity inherent in the continuous solution. At the same time, the discrete solution is close to the continuum Reissner-Nordstr"om one at large distances.

  1. [2112.12861] - Quantum geodesics on $λ$-Minkowski spacetime - Chengcheng Liu, Shahn Majid

  2. [2112.13103] - Galaxy rotation curves in multi-fractional spacetimes - Gianluca Calcagni, Gabriele U. Varieschi

  3. [2112.13216] - Quantum gravity corrections to the matter dynamics in the presence of a reference fluid - Giulia Maniccia, Giovanni Montani

  4. [2112.12828] - Gravity and the Crossed Product - Edward Witten

Mon - 12/27/21

Effective dynamics of scalar cosmological perturbations from quantum gravity

  • Authors: Luca Marchetti, Daniele Oriti
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2112.12677
  • Abstract We derive an effective dynamics for scalar cosmological perturbations from quantum gravity, in the framework of group field theory (GFT) condensate cosmology. The emergent spacetime picture is obtained from the mean field hydrodynamic regime of the fundamental theory, and physical observables are defined using a relational strategy applied at the same level of approximation, in terms of suitable collective states of the GFT field. The dynamical equations we obtain for volume and matter perturbations lead to the same solutions as those of classical general relativity in the long-wavelength, super-horizon limit, but differ in other regimes. These differences could be of phenomenological interest and make contact between fundamental quantum gravity models and cosmological observations, indicating new physics or limitations of the fundamental models or of the approximations leading to the effective cosmological dynamics.

There is no new related paper today

  1. [2112.12235] - Quantum Gravity at Low Energies - David Wallace

  2. [2112.12156] - Emergent times in holographic duality - Samuel Leutheusser, Hong Liu

  3. [2112.12198] - Engineering holographic flat fermionic bands - Nicolás Grandi, Vladimir Juričić, Ignacio Salazar Landea, Rodrigo Soto-Garrido

New papers last week