Fri - 02/16/24

There is no new related paper today

There is no new related paper today

  1. [2402.09686] - Lorentz violation induces isospectrality breaking in Einstein-Bumblebee gravity theory - Wentao Liu, Xiongjun Fang, Jiliang Jing, Jieci Wang

  2. [2402.09918] - Quantum gravity phenomenology and the blackbody radiation - R. Turcati, I. Soares, S. B. Duarte

  3. [2402.09981] - Resurgence in Lorentzian quantum cosmology: no-boundary saddles and resummation of quantum gravity corrections around tunneling saddles - Masazumi Honda, Hiroki Matsui, Kazumasa Okabayashi, Takahiro Terada

  4. [2402.09691] - When left and right disagree: Entropy and von Neumann algebras in quantum gravity with general AlAdS boundary conditions - Donald Marolf, Daiming Zhang

  5. [2402.10129] - Holographic covering and the fortuity of black holes - Chi-Ming Chang, Ying-Hsuan Lin

Thu - 02/15/24

Tunneling of quantum geometries in spinfoams

  • Authors: Pietro Dona, Hal M. Haggard, Carlo Rovelli, Francesca Vidotto
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.09038
  • Abstract Quantum gravitational tunneling effects are expected to give rise to a number of interesting observable phenomena, including, in particular, the evolution of black holes at the end of their existence or the emergence of the early universe from a quantum phase. Covariant Loop Quantum Gravity provides a framework to study these phenomena, yet a precise identification of tunneling processes is still not known. Motivated by this question, we consider a related, simpler case, that of Ponzano-Regge amplitudes: we find a surprising and detailed analogy of a class of simple transition amplitudes with tunneling processes in non-relativistic quantum mechanics.

Tunneling of quantum geometries in spinfoams

  • Authors: Pietro Dona, Hal M. Haggard, Carlo Rovelli, Francesca Vidotto
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.09038
  • Abstract Quantum gravitational tunneling effects are expected to give rise to a number of interesting observable phenomena, including, in particular, the evolution of black holes at the end of their existence or the emergence of the early universe from a quantum phase. Covariant Loop Quantum Gravity provides a framework to study these phenomena, yet a precise identification of tunneling processes is still not known. Motivated by this question, we consider a related, simpler case, that of Ponzano-Regge amplitudes: we find a surprising and detailed analogy of a class of simple transition amplitudes with tunneling processes in non-relativistic quantum mechanics.
  1. [2402.08951] - Cosmology of unimodular Born-Infeld-$f(R)$ gravity - Salih Kibaroğlu, Sergei D. Odintsov, Tanmoy Paul

Wed - 02/14/24

Gravitational Collapse in Energy-momentum squared gravity: Nature of singularities

  • Authors: Prabir Rudra
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.07957
  • Abstract In this paper, we explore a collapsing scenario in the background of energy-momentum squared gravity (EMSG). EMSG claims to have terms that originate from the quantum gravity effects mimicking loop quantum gravity. As a result, the framework admits a bounce at a finite time thus avoiding a singularity. So the question that naturally arises: Is there any realistic chance of the formation of a black hole or the quantum gravity effects are strong enough to totally avoid such a pathology? Motivated by this we are interested in studying a gravitational collapse mechanism in the background of EMSG and investigate the fate of such a process. We model the spacetime of a massive star by the Vaidya metric and derive the field equations in EMSG. Then using the equations we go on to study a gravitational collapse mechanism, on two specific models of EMSG with different forms of curvature-matter coupling. The prime objective is to probe the nature of singularity (if formed) as the end state of the collapse. We see that none of the models generically admit the formation of black holes as the end state of collapse, but on the contrary, they support the formation of naked singularities. This can be attributed to the quantum fluctuations of the gravitational interactions at the fundamental level.

Cosmological Dynamics from Covariant Loop Quantum Gravity with Scalar Matter

  • Authors: Muxin Han, Hongguang Liu, Dongxue Qu, Francesca Vidotto, Cong Zhang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.07984
  • Abstract We study homogenous and isotropic quantum cosmology using the spinfoam formalism of Loop Quantum Gravity (LQG). We define a coupling of a scalar field to the 4-dimensional Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) spinfoam model. We employ the numerical method of complex critical points to investigate the model on two different simplicial complexes: the triangulations of a single hypercube and two connected hypercubes. We find nontrivial implications for the effective cosmological dynamics. In the single-hypercube model, the numerical results suggest an effective Friedmann equation with a scalar density that contains higher-order derivatives and a scalar potential. The scalar potential plays a role similar to a positive cosmological constant and drives an accelerated expansion of the universe. The double-hypercubes model resembles a symmetric cosmic bounce, and a similar effective Friedmann equation emerges with higher-order derivative terms in the effective scalar density, whereas the scalar potential becomes negligible.

Axial perturbations in Kantowski-Sachs spacetimes and hybrid quantum cosmology

  • Authors: Guillermo A. Mena Marugán, Andrés Mínguez-Sánchez
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.08307
  • Abstract Recently, there has been a growing interest in investigating homogeneous but anisotropic spacetimes owing to their relation with nonrotating, uncharged black hole interiors. We present a description of axial perturbations for a massless scalar field minimally coupled to this geometry. We truncate the action at the quadratic perturbative order and tailor our analysis to compact spatial sections. Perturbations are described in terms of perturbative gauge invariants, linear perturbative constraints, and their canonically conjugate variables. The entire set, encompassing perturbations and homogeneous degrees of freedom, is consolidated into a canonical one. We employ a hybrid approach to quantize this system, integrating a quantum representation of the homogeneous sector using Loop Quantum Cosmology techniques with a conventional field quantization of the perturbations.

An adiabatic approach to the trans-Planckian problem in Loop Quantum Cosmology

  • Authors: Luis J. Garay, Mario López González, Mercedes Martín-Benito, Rita B. Neves
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.08375
  • Abstract We study the scalar modes that, being observable today, were trans-Planckian before inflation, within the context of hybrid Loop Quantum Cosmology (LQC). We analyse the dynamics of these highly ultraviolet modes by introducing modified dispersion relations to their equations of motion and discuss the impact that these relations would introduce in the power spectrum by computing the adiabaticity coefficient. More precisely, we consider two different models compatible with observations for the standard linear dispersion relation which are based on different initial conditions for the perturbations and background. One of these models avoids the issue altogether by generating less $e$-folds of inflation, so that the observable modes are never trans-Planckian, whereas the other suffers (arguably softly) from the trans-Planckian problem. This shows that the existence of the trans-Planckian problem in LQC is model-dependent.

Cosmological Dynamics from Covariant Loop Quantum Gravity with Scalar Matter

  • Authors: Muxin Han, Hongguang Liu, Dongxue Qu, Francesca Vidotto, Cong Zhang
  • Subjects: General Relativity and Quantum Cosmology (gr-qc)
  • Arxiv link: https://arxiv.org/abs/2402.07984
  • Abstract We study homogenous and isotropic quantum cosmology using the spinfoam formalism of Loop Quantum Gravity (LQG). We define a coupling of a scalar field to the 4-dimensional Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) spinfoam model. We employ the numerical method of complex critical points to investigate the model on two different simplicial complexes: the triangulations of a single hypercube and two connected hypercubes. We find nontrivial implications for the effective cosmological dynamics. In the single-hypercube model, the numerical results suggest an effective Friedmann equation with a scalar density that contains higher-order derivatives and a scalar potential. The scalar potential plays a role similar to a positive cosmological constant and drives an accelerated expansion of the universe. The double-hypercubes model resembles a symmetric cosmic bounce, and a similar effective Friedmann equation emerges with higher-order derivative terms in the effective scalar density, whereas the scalar potential becomes negligible.

  1. [2402.07980] - Lanczos spectrum for random operator growth - Tran Quang Loc

  2. [2402.08052] - Jackiw-Teitelboim Gravity, Random Disks of Constant Curvature, Self-Overlapping Curves and Liouville $\text{CFT}_{1}$ - Frank Ferrari

  3. [2402.08471] - Holographic Turbulence From a Random Gravitational Potential - Yaron Oz, Sebastian Waeber, Amos Yarom

  4. [2402.08555] - In-in correlators and scattering amplitudes on a causal set - Emma Albertini, Fay Dowker, Arad Nasiri, Stav Zalel

Tue - 02/13/24

There is no new related paper today

A new 2+1 coherent spin-foam vertex for quantum gravity

  • Authors: José Diogo Simão
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2402.05993
  • Abstract We propose an explicit spin-foam amplitude for Lorentzian gravity in three dimensions. The model is based on two main requirements: that it should be structurally similar to its well-known Euclidean analog, and that geometricity should be recovered in the semiclassical regime. To this end we introduce new coherent states for space-like 1-dimensional boundaries, derived from the continuous series of unitary $\mathrm{SU}(1,1)$ representations. We show that the relevant objects in the amplitude can be written in terms of the defining representation of the group, just as so happens in the Euclidean case. We derive an expression for the semiclassical amplitude at large spins, showing that it relates to the Lorentzian Regge action.
  1. [2402.06080] - Fixed Lines in Four Fermion Models in Two Dimensions - Sidan A, Tom Banks

Mon - 02/12/24

There is no new related paper today

A new 2+1 coherent spin-foam vertex for quantum gravity

  • Authors: José Diogo Simão
  • Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
  • Arxiv link: https://arxiv.org/abs/2402.05993
  • Abstract We propose an explicit spin-foam amplitude for Lorentzian gravity in three dimensions. The model is based on two main requirements: that it should be structurally similar to its well-known Euclidean analog, and that geometricity should be recovered in the semiclassical regime. To this end we introduce new coherent states for space-like 1-dimensional boundaries, derived from the continuous series of unitary $\mathrm{SU}(1,1)$ representations. We show that the relevant objects in the amplitude can be written in terms of the defining representation of the group, just as so happens in the Euclidean case. We derive an expression for the semiclassical amplitude at large spins, showing that it relates to the Lorentzian Regge action.
  1. [2402.06080] - Fixed Lines in Four Fermion Models in Two Dimensions - Sidan A, Tom Banks

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