Fri - 02/24/23

Twisted geometries are area-metric geometries

  • Authors: Bianca Dittrich, José Padua-Argüelles
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2302.11586
  • Abstract The quantum geometry arising in Loop Quantum Gravity has been known to semi-classically lead to generalizations of length-geometries. There have been several attempts to interpret these so called twisted geometries and understand their role and fate in the continuum limit of the spin foam approach to quantum gravity. In this paper we offer a new perspective on this issue by showing that the twisted geometry of a 4-simplex can be understood as arising from an area-metric (in contrast to the more particular length-metric). Such equivalence allows us to define notions like signature, generalized triangle inequalities and parallel transport for twisted geometries (now understood in a 4-dimensional setting), exemplifying how it provides a new handle to understand them. Furthermore, it offers a new microscopic understanding of spin foam geometries which is notably supported by recent studies of the continuum effective dynamics of spin foams.

Twisted geometries are area-metric geometries

  • Authors: Bianca Dittrich, José Padua-Argüelles
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2302.11586
  • Abstract The quantum geometry arising in Loop Quantum Gravity has been known to semi-classically lead to generalizations of length-geometries. There have been several attempts to interpret these so called twisted geometries and understand their role and fate in the continuum limit of the spin foam approach to quantum gravity. In this paper we offer a new perspective on this issue by showing that the twisted geometry of a 4-simplex can be understood as arising from an area-metric (in contrast to the more particular length-metric). Such equivalence allows us to define notions like signature, generalized triangle inequalities and parallel transport for twisted geometries (now understood in a 4-dimensional setting), exemplifying how it provides a new handle to understand them. Furthermore, it offers a new microscopic understanding of spin foam geometries which is notably supported by recent studies of the continuum effective dynamics of spin foams.

  1. [2302.12064] - Shadows and photon rings of regular black holes and geonic horizonless compact objects - Gonzalo J. Olmo, João Luís Rosa, Diego Rubiera-Garcia, Diego Sáez-Chillón Gómez

  2. [2302.11863] - JT Gravity on a Finite Lorentzian Strip: Time dependent Quantum Gravity Amplitudes - J. A. Rosabal

Thu - 02/23/23

There is no new related paper today

There is no new related paper today

  1. [2302.11210] - The Axion-Instanton Weak Gravity Conjecture and Scalar Fields - Clemens Vittmann

Wed - 02/22/23

Observational tests of quantum extension of Schwarzschild spacetime in loop quantum gravity with stellar stars in the galactic center

  • Authors: Jian-Ming Yan, Cheng Liu, Tao Zhu, Qiang Wu, Anzhong Wang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2302.10482
  • Abstract In this paper, we use the publicly available observational data of 17 stellar stars orbiting Sgr A* to test the quantum extension of Schwarzschild spacetime in loop quantum gravity (LQG). For our purpose, we transform the geodesical evolution of a massive particle in the quantum-extended Schwarzschild black hole to the perturbed Kepler problem and calculate the effects of LQG on the pericentre advance of the stellar stars. With these effects, one is able to compare them with the publicly available astrometric and spectroscopic data of stellar stars in the galactic center. We perform Monte Carlo Markov Chain (MCMC) simulations to probe the possible LQG effects on the orbit of S-stars. No significant evidence of the quantum-extended Schwarzschild black hole from LQG is found. Among the posterior analyses of 17 S-stars, the result of S2 gives the strongest bound on the LQG parameter $A_\lambda$, which places an upper bound at 95\% confidence level on $A_\lambda$ to be $A_\lambda < 0.302$.

Singularity resolution by holonomy corrections: Spherical charged black holes in cosmological backgrounds

  • Authors: Asier Alonso-Bardaji, David Brizuela, Raül Vera
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2302.10619
  • Abstract We study spherical charged black holes in the presence of a cosmological constant with corrections motivated by the theory of loop quantum gravity. The effective theory is constructed at the Hamiltonian level by introducing certain correction terms under the condition that the modified constraints form a closed algebra. The corresponding metric tensor is then carefully constructed ensuring that the covariance of the theory is respected, that is, in such a way that different gauge choices on phase space simply correspond to different charts of the same spacetime solution. The resulting geometry is characterized by four parameters: the three usual ones that appear in the general relativistic limit (describing the mass, the charge, and the cosmological constant), as well as a polymerization parameter, which encodes the quantum-gravity corrections. Contrary to general relativity, where this family of solutions is generically singular, in this effective model the presence of the singularity depends on the values of the parameters. The specific ranges of values that define the family of singularity-free spacetimes are explicitly found, and their global structure is analyzed. In particular, the mass and the cosmological constant need to be nonnegative to provide a nonsingular geometry, while there can only be a bounded, relatively small, amount of charge. These conditions are suited for any known spherical astrophysical black hole in the de Sitter cosmological background, and thus this model provides a globally regular description for them.

There is no new related paper today

  1. [2302.10582] - Covariant Growth Dynamics - Stav Zalel

  2. [2302.10832] - On QFT in Curved Spacetime from Quantum Gravity: proper WKB decomposition of the gravitational component - Giulia Maniccia, Giovanni Montani, Stefano Antonini

  3. [2302.10256] - Measuring the Homogeneity (or Otherwise) of the Quantum Universe - R. Loll, A. Silva

Tue - 02/21/23

There is no new related paper today

Generalized Abelian Turaev-Viro and $\mathrm{U}!\left(1\right)$ BF Theories

  • Authors: Emil Høssjer, Philippe Mathieu, Frank Thuillier
  • Subjects: Mathematical Physics (math-ph)
  • Arxiv link: https://arxiv.org/abs/2302.09191
  • Abstract We explain how it is possible to study $\mathrm{U}!\left(1\right)$ BF theory over a connected closed oriented smooth $3$-manifold in the formalism of path integral thanks to Deligne-Beilinson cohomology. We show how we can straightforwardly extend the definition to families of theories in any dimension. We extend then the definition of the Turaev-Viro invariant of a connected closed oriented smooth $3$-manifold in an Abelian framework to a family of invariants in any dimension. We show that those invariants can be written as discrete BF theories. We explain how the extensions of $\mathrm{U}!\left(1\right)$ BF theory we defined can be related to the extensions of Turaev-Viro invariant we constructed.

  1. [2302.09090] - Possible Relation between the Cosmological Constant and Standard Model Parameters - Mark P. Hertzberg, Abraham Loeb

  2. [2302.09219] - Complex saddles of three-dimensional de Sitter gravity via holography - Heng-Yu Chen, Yasuaki Hikida, Yusuke Taki, Takahiro Uetoko

Mon - 02/20/23

Non-singular flat universes in braneworld and Loop Quantum Cosmology

  • Authors: Rikpratik Sengupta, B. C. Paul, M. Kalam, P. Paul, A. Aich
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2302.09062
  • Abstract In this paper we take matter source with non-linear Equation of state (EoS) that has produced non-singular Emergent cosmology for spatially flat universe in General Relativity and minimally coupled scalar field with two different potentials that produce an inflationary emergent universe for positive spatial curvature in the relativistic context. We study all these three cases both in the context of Randall-Sundrum braneworld and effective Loop quantum cosmology (LQC) for zero spatial curvature that is observationally favoured and in the absence of any effective cosmological constant term. We solve the modified Friedmann equation in each case to obtain the time evolution of the scale factor and use it to check whether the initial singularity can be averted. In almost all the cases we find the initial singularity is absent. We study the nature of the slow roll inflation in the cases where we obtain inflationary emergent universes. The inflationary scenario is found to be improved than in a standard relatvistic context and we compare the improved scenario for both the braneworld and LQC models. Interestingly, we also obtain bouncing and cyclic universes from our analysis in some cases. We find that the initial singularity can be averted for a spatially flat universe with specific choice of matter EoS or scalar field potential, which do not violate the Null Energy condition in most cases, taking into account effective high energy (curvature) corrections with or without extra dimensions.

There is no new related paper today

  1. [2302.08804] - Stress-energy tensor correlations across regular black holes horizons - Matteo Fontana, Massimiliano Rinaldi

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