Article
Astronomy & Astrophysics
Cyril Renevey, Killian Martineau, Aurelien Barrau
Summary: This study investigates the influence of generalized corrections in loop quantum cosmology, finding that a long enough inflation phase can be generated by purely quantum geometrical effects, but also highlighting the limitations of this scenario. Additionally, the effects of generalized holonomy corrections on an inflationary phase generated by a massive scalar field are studied, and the consequences on the primordial scalar power spectrum are examined in detail. These results are actually quite general and can be applied beyond the loop framework.
Article
Astronomy & Astrophysics
Bao-Fei Li, Sahil Saini, Parampreet Singh
Summary: This study explores a unified phenomenological model combining matter bounce and ekpyrotic scenarios in loop quantum cosmology, analyzing the background dynamics and power spectrum of comoving curvature perturbations numerically. The analysis shows that the magnitude of the power spectrum changes during evolution, and the bouncing regime only leaves imprints on modes outside the scale-invariant regime. Further improvements in this model are necessary due to inconsistency with observational data in terms of the spectral index.
Article
Astronomy & Astrophysics
Mathias Garny, Petter Taule
Summary: The study presents an algorithm that takes into account the full time- and scale-dependence of fluid dynamics to assess the impact of neutrino free-streaming on the matter power spectrum. Deviations above 1% for k > 0.15 h/Mpc at z = 0 and sub-percent agreement on weakly non-linear scales at z = 0.5 were found when using a commonly adopted scheme with cold dark matter+baryon perturbations and EdS kernels for computing non-linear corrections.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Maxime De Sousa, Killian Martineau, Cyril Renevey, Aurelien Barrau
Summary: The propagation of perturbations is investigated in the context of generalized holonomy corrections, ensuring closure of the deformed algebra of constraints. The primordial cosmological power spectra are calculated, and it is demonstrated that while the specific form of the correction does affect observables, the main results of loop quantum cosmology remain robust.
Article
Astronomy & Astrophysics
Beatriz Elizaga Navascues, Guillermo A. Mena Marugan, Santiago Prado
Summary: The paper analyzes the conditions necessary for a choice of vacuum state for cosmological perturbations to result in a power spectrum with no scale-dependent oscillations over time. Non-oscillating power spectra are considered optimal for gaining observational access to regimes near the bounce where loop quantum cosmology effects are significant. The study shows that non-oscillatory spectra can be consistently obtained using hyperbolic equations derived in the hybrid loop quantization approach.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Masatoshi Shoji, Eiichiro Komatsu
Summary: In this study, we computed the density and velocity power spectra, taking into account the effect of time- and scale-dependent growth of massive neutrino perturbations as well as the departure from Einstein-de-Sitter dynamics. We found significant deviations from the commonly adopted approximate treatment, highlighting the importance of including these effects in the analysis.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yu Han
Summary: This paper investigates the Hamiltonian constraint of scalar-tensor theories (STTs) in the Jordan frame using loop quantum cosmology. Three different effective Hamiltonian constraints are obtained, leading to drastically different effective equations of motion. The implications of each set of effective equations of motion are discussed in detail. Furthermore, the effective dynamics of a specific model of STTs with a non-minimal coupling function and self-interacting quartic potential are studied, revealing different features and the existence of a cosmological bounce.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Pritha Paul, Chris Clarkson, Roy Maartens
Summary: This paper examines the computation of wide-angle corrections to the galaxy power spectrum, considering redshift-space distortions and relativistic Doppler corrections. It also includes multiple tracers with varying clustering, magnification, and evolution biases. The study emphasizes the importance of including the relativistic Doppler contribution and radial derivative terms for a consistent wide-angle expansion in large-scale surveys. Additionally, the authors present the wide-angle cross-power spectrum associated with the Doppler magnification-galaxy cross-correlation, which offers a new approach to test general relativity. The paper also introduces a method to analytically compute integrals involving products of spherical Bessel functions in the full-sky power spectrum.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Beatriz Elizaga Navascues, Guillermo A. Menagan, Santiago Prado
Summary: This study examines the compatibility of the quantum homogeneity and isotropy hypothesis with the requirement for a non-oscillatory power spectrum in loop quantum cosmology. It identifies a step in the procedure followed by the authors that is not clearly specified, relating to the switch from one set of states allowed by the hypothesis to a more manageable alternative set. The research shows that the criteria for restricting the vacuum state in LQC are compatible and not mutually exclusive.
Article
Astronomy & Astrophysics
Damiano Anselmi
Summary: In this study, inflationary perturbation spectra and the quantity r + 8n(T) were computed to the next-to-next-to-leading log order in quantum gravity with solely virtual particles. The spectra are functions of inflationary running coupling and satisfy cosmic renormalization group flow equations. Tensor fluctuations receive contributions from the spin-2 fakeon chi(mu nu), while the scalar spectrum's dependence on chi(mu nu) starts from alpha(2) corrections. The theoretical predictions have errors ranging from alpha(4) to alpha(3), and nontrivial issues regarding the fakeon projection at higher orders are discussed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Patrick Fraser
Summary: In this paper, the fluctuations of Gaussian states in LQC are derived, showing that they diverge as the state variance increases contrary to ordinary quantum mechanics. However, by scaling the holonomy length with a volume regularization parameter, these fluctuations can be arbitrarily suppressed.
Article
Astronomy & Astrophysics
Francesco Sartini, Marc Geiller
Summary: In this study, the quantum dynamics of the homogeneous black hole interior spacetime are investigated using the unimodular formulation of general relativity. By selecting appropriate variables, it is demonstrated how these models evolve through the singularity in loop quantum cosmology while remaining sharply peaked.
Article
Physics, Particles & Fields
Xiangdong Zhang
Summary: This paper extends the thermodynamic properties of loop quantum cosmology (LQC) to a new model with the Lorentz term, showing that the effective density and effective pressure in the modified Friedmann equation not only determine the evolution of the universe but also serve as thermodynamic quantities. The first law of thermodynamics of LQC remains valid with the help of the Misner-Sharp energy, providing precise physical meaning to the effective matter density and effective pressure.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Rodolfo Gambini, Jorge Pullin, Aureliano Skirzewski
Summary: The holonomy of generic extended loops is not gauge covariant, but a new approach is presented in this paper to define a family of extended loops that overcomes this issue. Sufficient conditions for extended loops to yield covariant holonomies are also provided. This opens up the possibility for a quantum representation of Yang-Mills theories and gravity based on extended loops.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Bao-Fei Li, Parampreet Singh
Summary: We investigate how different loop quantization prescriptions affect the formation of trapped surfaces in gravitational collapse, focusing on the mu o scheme and its drawbacks, as well as the improved dynamics in the mu over bar scheme. It is found that trapped surfaces do not form in the mu o scheme for a nonsingular collapse of homogeneous dust cloud unless certain conditions are met, while black holes can form in the mu over bar scheme and other lattice refinements determined by quantum geometry.