Article
Astronomy & Astrophysics
Sandipan Sengupta
Summary: This paper presents a Hamiltonian theory of gravity for noninvertible tetrad fields, which exhibit three local degrees of freedom. The formulation here provides a Hamiltonian basis to analyze gravity theory around a physical singularity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Adria Delhom, Gonzalo J. Olmo, Parampreet Singh
Summary: In loop quantum cosmology, the singularity of the big bang is resolved by a big bounce, even when modified quantization prescriptions are used. These non-singular models are related to metric-affine f (R) theories and can accurately approximate the effective dynamics of loop quantum cosmology in all regimes. The non-perturbative effects of these loop cosmologies are universally encoded by a logarithmic correction that depends on the bounce curvature of the model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
D. Jackson, R. Bufalo
Summary: In this work, the improved Deser-Woodard non-local gravity over five different cosmological models is analyzed, aiming to avoid the initial singular state of the universe. The numerical solution for the non-local distortion function is developed using the reconstruction procedure, providing viable cosmological solutions. The physical aspects and outcomes of the distortion function evolution at the bouncing point for each model are discussed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Alexander F. Jercher, Daniele Oriti, Andreas G. A. Pithis
Summary: In this study, we investigate the cosmological sector of the Lorentzian Barrett-Crane model and find that it exhibits homogeneous and isotropic cosmological dynamics similar to the SU(2)-based EPRL model. By using continuous SL(2, C) representations, we derive generalized Friedmann equations that show a quantum bounce and can reproduce all the features of the cosmological dynamics in the EPRL model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
A. Minkevich
Summary: The article discusses gravitational interactions in the Riemann-Cartan space-time, focusing on the transition of gravitational forces from repulsion to attraction under different energy densities. It also analyzes the conversion to the Friedman regime and the transition to gravitational repulsion at very low energy densities.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Mathematics
Igor Rodnianski, Yakov Shlapentokh-Rothman
Summary: This work focuses on the mathematical study of naked singularities for the Einstein vacuum equations in 3 + 1 dimensions. The solutions constructed correspond to the exterior region of a naked singularity. A new type of self-similarity for the Einstein vacuum equations is introduced, along with a new geometric twisting phenomenon that plays a significant role in singularity formation. Prior to this work, examples of naked singularities were limited to specific solutions in different contexts.
ANNALS OF MATHEMATICS
(2023)
Article
Astronomy & Astrophysics
Martin Bojowald, Pip Petersen
Summary: Quasiclassical methods are applied to an oscillating universe model, revealing that the oscillating dynamics is much less regular than in the classical description, even when the parameters do not change.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Martin Bojowald, Brenda Jones
Summary: Quasiclassical methods are used to determine dynamical tunneling times in quantum cosmological bounce models, showing that even with large barriers, tunneling times remain short, highlighting the quantum instability of the underlying models.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Sanjar Shaymatov, Naresh Dadhich
Summary: In higher dimensions, the repulsion due to rotation dominates over the attraction due to mass, preventing the overspinning of a black hole even with linear order accretion. For pure Lovelock rotating black holes, a specific dimensional threshold must be met to adhere to the weak cosmic censorship conjecture.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Stephen Appleby, Reginald Christian Bernardo
Summary: This paper introduces a potential means of self-tuning and a new exact Milne solution in a simple tadpole plus cubic-Galileon scalar-tensor theory. The study shows that the Milne solution is not an attractor but depends on the initial conditions for its asymptotic states.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Karim Mosani, Dipanjan Dey, Pankaj S. Joshi, Gauranga C. Samanta, Harikrishnan Menon, Vaishnavi D. Patel
Summary: In this study, we investigate the global causal structure of the end state of a spherically symmetric marginally bound Lemaitre-Tolman-Bondi (LTB) collapsing cloud in the framework of modified gravity. We find that the matching surface of the interior and the exterior metric can change for different values of alpha, which can alter the causal property of the first central singularity. We provide a numerical example to illustrate this change. Additionally, we show that for a globally naked singularity to be physically relevant, the first central singularity should be a nodal point.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
J. Leo Kim, Ghazal Geshnizjani
Summary: The study explores the cosmological bounce model based on Cuscuton gravity and finds that scale-invariant entropy modes can be generated when the auxiliary field is kinetically coupled to the primary field. The Cuscuton bounce solution is free of singularities and does not require ad hoc matching conditions. Furthermore, the study shows that while tensor modes in Cuscuton bounce are stable, the produced spectrum is strongly blue and not observable.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
James Wheeler
Summary: This paper investigates the occurrence of naked singularities in the Vaidya spacetimes. The study finds that globally naked singularities are more common than previously emphasized in the literature. Additionally, it is shown that the curvature strength of the singularity cannot be smoothed away in these spacetimes.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
George Lazarides, Rinku Maji, Qaisar Shafi
Summary: Investigated the impact of Coleman-Weinberg inflation on the stochastic gravity wave background spectrum emitted by intermediate-scale cosmic strings, finding it can help satisfy the PPTA bound. Explored the formation of strings, modified gravity wave spectra, and the results in different scenarios.
Article
Physics, Particles & Fields
J. Ambjorn, Z. Drogosz, J. Gizbert-Studnicki, A. Gorlich, J. Jurkiewicz, D. Nemeth
Summary: By using computer simulations, the geometry of a typical quantum universe is studied with coordinate defined by classical scalar fields. The field configurations reveal cosmic web structures similar to the present-day universe.
EUROPEAN PHYSICAL JOURNAL C
(2021)
