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
Tom Rudelius
Summary: A popular proposal for resolving the Hubble tension involves early dark energy models driven by an axion field. However, these models are tightly constrained by the axion weak gravity conjecture, making it challenging to realize them in a UV complete theory of quantum gravity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
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
J. Chojnacki, J. Krajecka, J. H. Kwapisz, O. Slowik, A. Strag
Summary: This article explores the relationship between eternal inflation and the asymptotic safety hypothesis in other approaches to quantum gravity. It reveals that there is no tension between eternal inflation and asymptotic safety in both the matter and gravitational sectors, contrary to string theory. Additionally, it suggests that eternal inflation is not possible within the range of applicability of effective field quantum gravity theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Sandeep Aashish, Sukanta Panda, Abbas Altafhussain Tinwala, Archit Vidyarthi
Summary: In this work, the calculation of the divergent part of one-loop covariant effective action for scalar fields coupled to gravity was developed using the generalized Schwinger-DeWitt technique. New terms in the one-loop corrections were derived and compared with past literature. Additionally, the covariant versions of past results were obtained by extending the ordinary Schwinger-DeWitt approach with Barvinsky and Vilkovisky's method. The one-loop gravitational corrections for a dilaton-extended two-field Starobinsky model were also studied and compared with existing results.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
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
Astronomy & Astrophysics
Astrid Eichhorn, Rafael R. Lino dos Santos, Fabian Wanger
Summary: In this study, we investigate whether Horndeski gravity can be more than just a phenomenological model and become a fundamental theory incorporating quantum effects at high energy scales. We find that within the asymptotic-safety paradigm, it is possible to achieve an ultraviolet completion of a certain class of Horndeski gravity models. However, the couplings required by these models are incompatible with dynamical dark energy. Similarly, under the assumption of no new strongly-coupled physics below the Planck scale, quantum gravity fluctuations limit the Horndeski couplings, making it difficult to explain dynamical dark energy.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Claus Kiefer, Tatevik Vardanyan
Summary: We calculate the power spectrum of primordial quantum fluctuations in an inflationary universe with curvature parameter kappa = 1 using gauge-invariant variables and a Born-Oppenheimer approximation scheme. Compared to the flat model, the closed model shows a deficit of power at large scales.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Alberto Salvio
Summary: The recent results of the BICEP and Keck collaborations have placed tight constraints on many inflationary models. One possible way to avoid these constraints is by introducing quadratic-in-curvature terms that can UV complete gravity while respecting stability and unitarity. The predictions of quadratic gravity are computed and compared with the BICEP/Keck constraints in two inflationary scenarios, (critical) Higgs inflation and natural inflation, which are already ruled out in Einstein gravity. It is shown that quadratic gravity can restore agreement with the observational constraints in both scenarios.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Multidisciplinary
M. J. Luo
Summary: This article proposes and reviews a framework of quantum spacetime reference frame, in which the quantum spacetime is deformed by the Ricci flow at the Gaussian approximation. It is found that the Ricci flow can be applied to the high curvature region near the local singularity of the early universe, and can naturally reproduce an inflationary deSitter universe without introducing any inflaton field. The deviation from exact deSitter can be calculated by a small deviation from the singular flow-time via the Ricci flow, and the power spectrum of the scalar perturbation agrees with current observations.
Article
Physics, Multidisciplinary
A. Kashlinsky
Summary: The study focuses on the effects of advection motion of dark matter and baryons in inflation-based cosmology on early structure formation, suggesting a delayed formation of early objects and efficient common motion of DM and baryon components on scales relevant for collapse and formation of first luminous sources. This leads to an easier explanation for the existence of supermassive black holes observed in quasars at high z > 7.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Vijay Nenmeli, S. Shankaranarayanan, Vasil Todorinov, Saurya Das
Summary: This study utilizes the Generalized Uncertainty Principle to model features of quantum gravity and explores the applications of Stelle gravity in cosmology. It shows that Stelle gravity can be considered as a classical manifestation of maximum momentum and the GUP. Strong constraints on the GUP parameter are obtained from CMB observations, providing both lower and upper bounds.
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
Adria Gomez-Valent, Ziyang Zheng, Luca Amendola, Valeria Pettorino, Christof Wetterich
Summary: The study reveals that the fraction of early dark energy (EDE) is constrained to be around 0.4%, and its impact on cosmological tensions is significant, although constraints considerably weaken when the sound speed is allowed to vary. The presence of EDE in different epochs helps both alleviate and worsen cosmological tensions.
Article
Astronomy & Astrophysics
Jisuke Kubo, Jeffrey Kuntz, Jonas Rezacek, Philipp Saake
Summary: We investigate the effects of gravitational degrees of freedom on inflationary parameters in a generic model of quadratic gravity coupled to a single scalar. Our findings show that quantum corrections from the massive spin-2 ghost contribute significantly to the effective inflationary potential, enabling the spontaneous breakdown of global scale invariance without the need for additional scalar fields. We compute inflationary parameters and compare them to well-known inflationary models, finding that they fit within the constraints set by the Planck and BICEP/Keck collaborations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jonathan Braden, J. Richard Bond, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Astronomy & Astrophysics
Jonathan Braden, J. Richard Bond, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Astronomy & Astrophysics
J. Richard Bond, Jonathan Braden, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Astronomy & Astrophysics
Laura Mersini-Houghton
CLASSICAL AND QUANTUM GRAVITY
(2016)
Article
Astronomy & Astrophysics
Fred C. Adams, Stephon Alexander, Evan Grohs, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2017)
Article
Astronomy & Astrophysics
Eleonora Di Valentino, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2017)
Article
Astronomy & Astrophysics
Eleonora Di Valentino, Laura Mersini-Houghton
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2017)
Article
Astronomy & Astrophysics
Laura Mersini-Houghton, Malcolm J. Perry
CLASSICAL AND QUANTUM GRAVITY
(2014)
Article
Astronomy & Astrophysics
Laura Mersini-Houghton, Malcolm J. Perry
CLASSICAL AND QUANTUM GRAVITY
(2014)
Article
Astronomy & Astrophysics
Laura Mersini-Houghton
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2014)
Article
Astronomy & Astrophysics
Laura Mersini-Houghton
Article
Multidisciplinary Sciences
Eleonora Di Valentino, Laura Mersini-Houghton
Article
Astronomy & Astrophysics
Laura Mersini-Houghton
CLASSICAL AND QUANTUM GRAVITY
(2017)
Proceedings Paper
Physics, Particles & Fields
Laura Mersini-Houghton, Adam Kelleher
NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS
(2009)