Fri - 09/24/21

There is no new related paper today

There is no new related paper today

  1. [2109.10932] - Violent nonlinear collapse in the interior of charged hairy black holes - Maxime Van de Moortel

  2. [2109.11092] - Angular correlations of causally-coherent primordial quantum perturbations - Craig Hogan, Stephan S. Meyer

  3. [2109.10961] - Swampland Constraints on Neutrino Masses - E. Gonzalo, L.E. Ibáñez, I. Valenzuela

Thu - 09/23/21

The Physical Relevance of the Fiducial Cell in Loop Quantum Cosmology

  • Authors: Fabio M. Mele, Johannes Münch
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2109.10663
  • Abstract A common way to avoid divergent integrals in homogeneous spatially non-compact gravitational systems, as e.g. cosmology, is to introduce a fiducial cell by cutting-off the spatial slice at a finite region $V_o$. This is usually considered as an auxiliary integral regulator to be removed after performing computations by sending it to infinity. In this paper, we analyse the dependence of the classical and quantum theory of homogeneous, isotropic and spatially flat cosmology on this fiducial cell. We show that each fixed $V_o$ regularisation leads to a different canonically independent theory. At the classical level, the dynamics of observables is not affected by the regularisation choice on-shell. For the quantum theory, however, this leads to a family of regulator dependent quantum representations labelled by $V_o$ and the limit $V_o\to\infty$ becomes then more subtle. First, we construct a novel isomorphism between different $V_o$-regularisations, which allows us to identify states in the different $V_o$-labelled Hilbert spaces to ensure equivalent dynamics for any value of the regulator. The $V_o \rightarrow \infty$ limit would then correspond to choosing a state for which the volume assigned to the fiducial cell becomes infinite. As second main result of our analysis, by looking at observables respectively smeared over the fiducial cell $V_o$ and subregions $V$, we find that quantum fluctuations of the latter explicitly depend on the size of the fiducial cell. Physically relevant fluctuations for a finite region, as e.g. in the early time regime, would then be unreasonably suppressed in the limit where the volume of the fiducial cell becomes infinite. Our results suggest that the fiducial cell is not playing the role of a mere regularisation but is physically relevant at the quantum level and complement previous statements in the literature based on different arguments.

There is no new related paper today

  1. [2109.10749] - If time had no beginning: growth dynamics for past-infinite causal sets - Bruno Valeixo Bento, Fay Dowker, Stav Zalel

Wed - 09/22/21

Quantum Holography from Fermion Fields

  • Authors: Paola Zizzi
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
  • Arxiv link: https://arxiv.org/abs/2109.10236
  • Abstract We demonstrate, in the context of Loop Quantum Gravity, the Quantum Holographic Principle, according to which the area of the boundary surface enclosing a region of space encodes a qubit per Planck unit. To this aim, we introduce fermion fields in the bulk, whose boundary surface is the two-dimensional sphere. The doubling of the fermionic degrees of freedom and the use of the Bogoljubov transformations lead to pairs of spin network’s edges piercing the boundary surface with double punctures, giving rise to pixels of area encoding a qubit. The proof is also valid in the case of a fuzzy sphere.

There is no new related paper today

  1. [2109.09814] - Dynamics and Observational Signatures of Shell-like Black Hole Mimickers - Ulf Danielsson, Luis Lehner, Frans Pretorius

  2. [2109.10017] - Black holes as frozen stars - Ram Brustein, A.J.M. Medved, Tamar Simhon

  3. [2109.09753] - Graviton corrections to the Newtonian potential using invariant observables - M. B. Fröb, C. Rein, R. Verch

Tue - 09/21/21

There is no new related paper today

There is no new related paper today

  1. [2109.08696] - Bouncing with shear: Implications from quantum cosmology - Karthik Rajeev, Vikramaditya Mondal, Sumanta Chakraborty

  2. [2109.09638] - Time-space duality in 2D quantum gravity - Ding Jia

  3. [2109.09364] - Non-linear sigma models on constant curvature target manifolds: a functional renormalization group approach - Alexander N. Efremov, Adam Rançon

  4. [2109.09496] - Background Independent Field Quantization with Sequences of Gravity-Coupled Approximants II: Metric Fluctuations - Maximilian Becker, Martin Reuter

Mon - 09/20/21

An Overview on the Nature of the Bounce in LQC and PQM

  • Authors: Gabriele Barca, Eleonora Giovannetti, Giovanni Montani
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2109.08645
  • Abstract We present a review on basic aspects of quantum cosmology in the presence of cut-off physics. We first analyze how the Wheeler-DeWitt equation in a pure metric approach describes the quantum Universe, showing how the singularity is not removed. We then discuss basic features of loop quantum cosmology. For the isotropic Universe, we compare the original $\mu_0$ scheme and the most commonly accepted formulation, the $\bar{\mu}$ scheme. Some results concerning the Bianchi Universes are also discussed. Finally, we consider some relevant criticisms on the real link between full loop quantum gravity and its minisuperspace implementation. In the second part of the review we consider the isotropic Universe and the Bianchi models in the framework of polymer quantum mechanics. We first address the polymerization in terms of the Ashtekar-Barbero-Immirzi connection and show how the resulting dynamics is isomorphic to the $\mu_0$. Then we analyze the polymerization of volume-like variables, and we see the resulting dynamics is isomorphic to the $\bar{\mu}$ scheme with a fixed critical energy density. Finally, we consider the polymer quantum dynamics of the homogeneous and inhomogeneous Mixmaster model through a metric approach. We compare the results obtained by using the volume variable to the standard Misner variable. In the latter case we find a cosmology that is still singular, and its chaotic properties depend on the ratio between the lattice steps for the isotropic and anisotropic variables. We conclude the review with some considerations on changing variables in the polymer representation. In particular we consider how the dynamics can be mapped in two different sets of variables (at the price of using a coordinate-dependent lattice step), and we infer some possible implications on the equivalence of the $\mu_0$ and $\bar{\mu}$ scheme of loop quantum cosmology.

There is no new related paper today

  1. [2109.08667] - Quantum gravity of dust collapse - Viqar Husain, Jarod George Kelly, Robert Santacruz, Edward Wilson-Ewing

  2. [2109.08563] - On the black hole/string transition - Yiming Chen, Juan Maldacena, Edward Witten

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