Fri - 07/08/22

Markov Chain Monte Carlo methods for graph refinement in covariant Loop Quantum Gravity

  • Authors: Pietropaolo Frisoni, Francesco Gozzini, Francesca Vidotto
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Computational Physics (physics.comp-ph)
  • Arxiv link: https://arxiv.org/abs/2207.02881
  • Abstract We adapt the Metropolis-Hastings algorithm, along with recently developed computational methods, to study the quantum regime in spinfoams with many degrees of freedom. This approach fills a gap in the current numerical methods for computing spinfoam observables in the low-spin regime of covariant Loop Quantum Gravity. We test the method by studying a refinement of the 4-simplex amplitude, where the boundary is refined from 5 to 20 boundary tetrahedra. We investigate the BF and Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) models, computing boundary geometrical operators, correlation functions and entanglement entropy. We are able to confirm that the transition amplitudes are stable against this refinement, even in the physically relevant EPRL case: the boundary geometry does not change on average, but the new degrees of freedom modify the quantum fluctuations of the boundary and the correlations between different spatial patches. The expectation values obtained numerically are compatible with their geometrical interpretation and, interestingly, the correlations between neighbouring patches decay sharply when computed across spinfoam vertices.

Markov Chain Monte Carlo methods for graph refinement in covariant Loop Quantum Gravity

  • Authors: Pietropaolo Frisoni, Francesco Gozzini, Francesca Vidotto
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Computational Physics (physics.comp-ph)
  • Arxiv link: https://arxiv.org/abs/2207.02881
  • Abstract We adapt the Metropolis-Hastings algorithm, along with recently developed computational methods, to study the quantum regime in spinfoams with many degrees of freedom. This approach fills a gap in the current numerical methods for computing spinfoam observables in the low-spin regime of covariant Loop Quantum Gravity. We test the method by studying a refinement of the 4-simplex amplitude, where the boundary is refined from 5 to 20 boundary tetrahedra. We investigate the BF and Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) models, computing boundary geometrical operators, correlation functions and entanglement entropy. We are able to confirm that the transition amplitudes are stable against this refinement, even in the physically relevant EPRL case: the boundary geometry does not change on average, but the new degrees of freedom modify the quantum fluctuations of the boundary and the correlations between different spatial patches. The expectation values obtained numerically are compatible with their geometrical interpretation and, interestingly, the correlations between neighbouring patches decay sharply when computed across spinfoam vertices.

Towards effective actions for the continuum limit of spin foams

  • Authors: Johanna N. Borissova, Bianca Dittrich
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2207.03307
  • Abstract Spin foams arise from a quantization of classical gravity expressed via the Plebanski action. Key open questions related to the continuum limit of spin foams are whether general relativity is reproduced and what type of corrections could emerge. As a central component for spin foam dynamics, recent results on the continuum limit of the Area Regge action suggest a close relation with actions for area metrics instead of a length metric. Inspired by these results, within the framework of modified Plebanski theory we construct a family of candidate actions for area metrics. These actions are expected to describe the continuum limit of spin foams and provide a starting point to explore phenomenological aspects of the large-scale dynamics of spin foams. More generally, they set the stage for exploring consequences of an enlargement of the configuration space for gravity from length to area metrics. The actions we construct lead to an effective action for the length metric, describing a non-local and ghost-free version of Einstein-Weyl gravity.
  1. [2207.03345] - Non-commutative Geometry from Perturbative Quantum Gravity - Markus Fröb, Albert Much, Kyriakos Papadopoulos

Thu - 07/07/22

There is no new related paper today

There is no new related paper today

  1. [2207.02689] - The birth of the Universe as a result of the change of the metric signature - T. P. Shestakova

  2. [2207.02814] - Towards an effective description of holographic vortex dynamics - Yu-Kun Yan, Shanquan Lan, Yu Tian, Peng Yang, Shunhui Yao, Hongbao Zhang

Wed - 07/06/22

Observational Predictions of LQG Motivated Polymerized Black Holes and Constraints From Sgr A* and M87*

  • Authors: Rahul Kumar Walia
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2207.02106
  • Abstract Loop Quantum Gravity (LQG) inspired partial polymer quantization in four-dimensional theory leads to a single-horizon quantum corrected globally regular black hole spacetime. The polymerized black hole metric is characterized by the minimum length parameter, $k$, and mimics the Schwarzschild black hole in the weak-field limit. We present an analytic and numerical investigation of the strong gravitational lensing and shadow morphology to determine the observational impacts of quantum effects. We calculate the characteristic changes in the lensing observables compared to those for the Schwarzschild black hole. It is interesting to note that the deflection angle, the angular separation between the outermost relativistic image, and magnification increase with $k$. Using the ray-tracing technique, we simulated the black hole shadows under three distinct accretion models: static spherical accretion, radially infalling spherical accretion, and the thin accretion disk model. Polymerized black holes’ shadow morphology strongly depends on $k$. Constraints on $k$ are derived for the M87* and Sgr A* black hole shadow observations from the Event Horizon Telescope. Our study suggests that quantum gravity effects are accessible in the astrophysical black holes’ observations.

There is no new related paper today

  1. [2207.02166] - Permutation symmetry in large N Matrix Quantum Mechanics and Partition Algebras - George Barnes, Adrian Padellaro, Sanjaye Ramgoolam

Tue - 07/05/22

There is no new related paper today

There is no new related paper today

  1. [2207.01080] - Spacetime Entanglement Entropy: Covariance and Discreteness - Abhishek Mathur, Sumati Surya, Nomaan X

  2. [2207.00605] - Entanglement Witnessing for Lattice Gauge Theories - Veronica Panizza, Ricardo Costa de Almeida, Philipp Hauke

Mon - 07/04/22

Gravitational Particle Production and the Validity of Effective Descriptions in Loop Quantum Cosmology

  • Authors: Gustavo S. Vicente, Rudnei O. Ramos, Leila L. Graef
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2207.00435
  • Abstract The effective approach in Loop Quantum Cosmology (LQC) has provided means to obtain predictions for observable quantities in LQC models. While an effective dynamics in LQC has been extensively considered in different scenarios, a robust demonstration of the validity of effective descriptions for the perturbative level still requires further attention. The consistency of the description adopted in most approaches requires the assumption of a test field approximation, which is limited to the cases in which the backreaction of the particles gravitationally produced can be safely neglected. Within the framework of LQC, some of the main approaches to quantize the linear perturbations are the dressed metric, the hybrid approaches and the closed/deformed algebra approach. Here, we analyze the consistency of the test field assumption in these frameworks by computing the energy density stored in the particles gravitationally produced compared to the background energy density. This analysis ultimately provides us with a consistency test of the effective descriptions of LQC.

Poisson brackets in Sobolev spaces: a mock holonomy-flux algebra

  • Authors: J Fernando Barbero G, Marc Basquens, Bogar Díaz, Eduardo J S Villaseñor
  • Subjects: Mathematical Physics (math-ph); General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2207.00342
  • Abstract The purpose of this paper is to discuss a number of issues that crop up in the computation of Poisson brackets in field theories. This is specially important for the canonical approaches to quantization and, in particular, for loop quantum gravity. We illustrate the main points by working out several examples. Due attention is paid to relevant analytic issues that are unavoidable in order to properly understand how computations should be carried out. Although the functional spaces that we use throughout the paper will likely have to be modified in order to deal with specific physical theories such as general relativity, many of the points that we will raise will also be relevant in that context. The specific example of the mock holonomy-flux algebra will be considered in some detail and used to draw some conclusions regarding the loop quantum gravity formalism.

There is no new related paper today

  1. [2207.00078] - *Testing Rotating Regular Spacetimes with EHT Results of Sgr A** - Rahul Kumar Walia, Sushant G Ghosh, Sunil D Maharaj

  2. [2207.00072] - Extremal Surfaces and Thin-shell Wormholes - Mariano Chernicoff, Gaston Giribet, Emilio Rubín de Celis

  3. [2207.00407] - Holography for people with no time - Henry W. Lin, Juan Maldacena, Liza Rozenberg, Jieru Shan

  4. [2207.00408] - Looking at supersymmetric black holes for a very long time - Henry W. Lin, Juan Maldacena, Liza Rozenberg, Jieru Shan

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