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Review
Astronomy & Astrophysics
Heliudson Bernardo et al.
Summary: The cosmological constant and its phenomenology continue to pose significant challenges in theoretical physics. This review explores potential modifications to Einstein's general relativity that could address the problems arising from the interplay of classical gravity and quantum field theory. Various approaches, such as constrained gravity, massive gravity, Horndeski theories, and models with extra dimensions, are discussed with their potential to solve the cosmological constant problems and align with observational data.
Article
Astronomy & Astrophysics
Alessio Belfiglio et al.
Summary: We explore a toy model mechanism of geometric cancellation to address the cosmological constant problem. We assume that vacuum energy during primordial times drives an inflationary quadratic hilltop potential that is nonminimally coupled to gravity. We demonstrate how vacuum energy release can transform into geometric particles and propose dark matter candidates constituted by geometric quasiparticles.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Eric Ling et al.
Summary: This paper studies Milne-like spacetimes, a class of hyperboloidal FLRW spacetimes that can have continuous extensions through the big bang process (t=0). By writing the metric in conformal Minkowskian coordinates and using the past asymptotic assumption of the scale factor, it is shown that a big bang extension exists. The research reveals that a scale factor satisfying a(t)=t+o(t) is not sufficient for a big bang extension, but it is necessary if its derivative converges as t tends to 0. Additionally, the parameter e in the scale factor a(t)=t+o(t( 1+e)) is not necessary for a big bang extension.
GENERAL RELATIVITY AND GRAVITATION
(2023)
Article
Physics, Nuclear
Reginald Christian Bernardo et al.
Article
Astronomy & Astrophysics
Sayantan Choudhury et al.
Journal of Cosmology and Astroparticle Physics
(2023)
Article
Astronomy & Astrophysics
Celia Escamilla-Rivera et al.
Summary: In this study, a specific self-tuning filter solution focused on a zero-curvature fixed point is used to investigate the H-0 tension in the context of the Fab-Four theory of gravity. The equations in this scheme restrict the universe's evolution to different scenarios, including radiation-like expansion, matter-like expansion, and late-time acceleration. By constructing the cosmographic series of the Fab-Four theory, the kinematic parameters such as the Hubble constant H-0 and the deceleration parameter q0 are obtained for all the mentioned scenarios. The results show that the current discrepancy on H-0 can be alleviated by incorporating specific requirements on the free parameters of the Fab-Four theory through a self-tuning filter.
Article
Astronomy & Astrophysics
Nemanja Kaloper
Summary: General covariant unimodular gravity frameworks, based on the Henneaux-Teitelboim formulation, are, in disguise, 4-form field theories corrected with higher dimension operators. In the presence of charged tensional membranes, de Sitter spaces in these theories are unstable and decay. If the fluxes sourced by membranes are mutually incommensurate, de Sitter geometries comprise a very refined discretuum of states. Whenever the 4-form sector is dominated by linear flux terms, the almost-Minkowski space becomes the unique long-time attractor, resulting in a tiny cosmological constant that doesn't require anthropic reasoning.
Article
Astronomy & Astrophysics
Alessio Belfiglio et al.
Summary: We investigate the entanglement due to geometric corrections in particle creation during inflation. We propose a single-field inflationary scenario, nonminimally coupled to the scalar curvature of spacetime, where particle production is purely geometric. The effects of the nonzero entanglement entropy on the primordial time of Universe evolution are studied, and the possibility of modeling the particle candidate in terms of dark matter is discussed. The classical backreaction of inhomogeneities on the homogeneous dynamical background degrees of freedom is also studied and quantified in the slow-roll regime.
Article
Astronomy & Astrophysics
Reginald Christian Bernardo et al.
Summary: This study explores the method of well-tempering in the context of Horndeski scalar-tensor gravity. It demonstrates that well-tempering is the unique approach to screen vacuum energy and obtain a late-time, low energy vacuum state. The research also shows the ability of well-tempering to accommodate self-tuned flat Minkowski solutions.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Edmund J. Copeland et al.
Summary: We explore a family of generalised scalar-tensor theories that exhibit self-tuning to low scale anti de Sitter vacua, even in the presence of a large cosmological constant. Due to a subtle interplay between weak scalar coupling and low scalar mass, these theories can self-tune and be compatible with solar system tests of gravity without non-linearities and unreliable screening mechanisms. The weak scalar coupling and slow response to vacuum energy phase transitions present interesting possibilities for connecting early universe inflation to the cancellation of vacuum energy.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Stephen Appleby et al.
Summary: This article studies the effects of variations in the degeneracy condition on scalar-tensor gravitational models. The study finds that the metric maintains an asymptotic Minkowski state when shift symmetry is preserved, but the asymptotic behavior can radically alter when shift symmetry is broken. Additionally, non-degenerate models have the attractive quality of having low energy, late-time asymptotic states that are independent of the vacuum energy.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Rocco D'Agostino et al.
Summary: This article proposes a cancellation mechanism to solve the cosmological constant problem by introducing a generalized scalar field, which is able to remove the vacuum energy contribution. The field is also investigated for its role in the overall evolution of the Universe, particularly in the formation of inflationary phase.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Osmin Lacombe et al.
Summary: In this study, the idea of self-tuning the observed cosmological constant to zero is reconsidered and promoted as a selection criterion for brane-world models. By requiring that the model ensures the vanishing of the 4D curvature of the maximally symmetric 3-brane world-volume independently of the effective vacuum energy, only two possibilities remain: one with a canonical bulk kinetic term and the other with an unconventional bulk kinetic term. The latter is selected as the unique possibility within the class of models.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Arnaz Khan et al.
Summary: This paper presents a minimal, self-tuning scalar field model that can dynamically cancel a large quantum vacuum energy and produce accelerated expansion. The model belongs to the Kinetic Gravity Braiding sub-class of Horndeski theory and is not excluded by observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Review
Astronomy & Astrophysics
Raul Carballo-Rubio et al.
Summary: Unimodular gravity (UG) is an alternative to general relativity (GR) with a different approach to the cosmological constant problem, but no further differences have been found.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Physics, Particles & Fields
Cristian Moreno-Pulido et al.
Summary: The renormalization of vacuum energy in quantum field theory can be problematic due to theoretical conundrums that arise during the process. However, by employing different perspectives and techniques, one can overcome these issues and obtain satisfactory results, such as smooth functions, running vacuum models, and the equation of state of quantum vacuum.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Reginald Christian Bernardo et al.
Summary: In this paper, the authors study self-tuning in teleparallel gravity for the first time and obtain well-tempered cosmological models. By expanding the well-tempered recipe to its most general form, the first well-tempered cosmologies in teleparallel gravity are found. The cosmological dynamics in a well-tempered model demonstrate the dynamical stability of the vacuum, compatibility with a matter era, and stability of the vacuum through a phase transition.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Eric Linder et al.
Summary: By counterposing the two seemingly intractable problems in cosmology, progress can be made. The research has found the connection between the kinetic term and braiding term, expanding previous studies on different term dependencies. This discovery will greatly reduce the number of parameters needed to test modified gravity against cosmological observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Reginald Christian Bernardo
Summary: The study focuses on the self-tuning subclass of kinetic gravity braiding and makes robust predictions on self-tuning and dynamics in the tadpole-free shift symmetric sector of the theory. It shows the inevitability of cosmic acceleration, proves the dynamical stability of the late-time asymptotic state, and derives ghost and gradient stability constraints on the self-tuning vacuum. The results are discussed concretely in the context of a generalized cubic covariant Galileon theory and an exponential kinetic gravity braiding.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Eric Ling
FOUNDATIONS OF PHYSICS
(2020)
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Astronomy & Astrophysics
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JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
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Astronomy & Astrophysics
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Astronomy & Astrophysics
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Astronomy & Astrophysics
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JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2019)
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Physics, Multidisciplinary
S. Carlip
PHYSICAL REVIEW LETTERS
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Astronomy & Astrophysics
Lucas Lombriser
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Astronomy & Astrophysics
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JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2018)
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Astronomy & Astrophysics
Orlando Luongo et al.
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Astronomy & Astrophysics
E. Babichev et al.
CLASSICAL AND QUANTUM GRAVITY
(2015)
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Physics, Particles & Fields
Sayantan Choudhury et al.
EUROPEAN PHYSICAL JOURNAL C
(2015)
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Astronomy & Astrophysics
Stephen Appleby
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Astronomy & Astrophysics
Nemanja Kaloper et al.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2014)
Article
Physics, Particles & Fields
Sayantan Choudhury et al.
Article
Astronomy & Astrophysics
C. P. Burgess et al.
PHYSICS OF THE DARK UNIVERSE
(2013)
Article
Astronomy & Astrophysics
Jerome Martin
COMPTES RENDUS PHYSIQUE
(2012)
Article
Astronomy & Astrophysics
Stephen A. Appleby et al.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2012)
Article
Astronomy & Astrophysics
Edmund J. Copeland et al.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2012)
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Astronomy & Astrophysics
Christos Charmousis et al.
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Physics, Multidisciplinary
Christos Charmousis et al.
PHYSICAL REVIEW LETTERS
(2012)
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Physics, Particles & Fields
P. Castorina et al.
EUROPEAN PHYSICAL JOURNAL C
(2007)
Article
Education, Scientific Disciplines
Claude Semay
EUROPEAN JOURNAL OF PHYSICS
(2007)
Review
Astronomy & Astrophysics
S Nojiri et al.
Article
Physics, Particles & Fields
Y Aghababaie et al.
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Astronomy & Astrophysics
S Mukohyama
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Physics, Multidisciplinary
S Mukohyama et al.
PHYSICAL REVIEW LETTERS
(2004)
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Astronomy & Astrophysics
J Garriga et al.
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Physics, Particles & Fields
C Csáki et al.