Article
Physics, Multidisciplinary
J. S. Goncalves, A. F. Santos
Summary: The hybrid metric-Palatini gravity theory describes a non-minimal coupling between matter and geometry, investigating the causal implications of its modified field equations on time and exploring both causal and non-causal solutions.
Article
Physics, Particles & Fields
Joao Luis Rosa, D. A. Ferreira, Dionisio Bazeia, Francisco S. N. Lobo
Summary: The study focuses on 5-dimensional braneworld scenarios within the scalar-tensor representation of the generalized hybrid metric-Palatini gravitational theory. It shows that all models are stable against small fluctuations of the metric and that the gravitational zero mode profile can be controlled by the model's parameters, particularly in the presence of an additional scalar field.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
J. S. Goncalves, A. F. Santos
Summary: The Palatini f(R,T) gravity theory allows for the replacement of the standard Einstein-Hilbert action with an arbitrary function of the Ricci scalar R and the trace T of the energy-momentum tensor, where the metric and connection are treated as independent variables, avoiding the occurrence of noncausal solutions.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2021)
Review
Physics, Mathematical
Francisco S. N. Lobo
Summary: The hybrid metric-Palatini approach is a successful gravitational theory that combines the advantages of metric and Palatini versions and avoids some drawbacks. This article explores the formulation of this hybrid approach and its achievements in passing local tests and applications in astrophysics and cosmology.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Minxi He, Yusuke Mikura, Yuichiro Tada
Summary: We extend the Higgs inflation to include non-minimal couplings between Higgs and both the metric-type and the Palatini-type Ricci scalars in hybrid metric-Palatini gravity. Our model realizes slow-roll inflation in the large-field regime with observationally favored predictions. We also explore the unitarity property of our model and discuss possible UV-extended theories to achieve a weakly-coupled effective field theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: In this study, we investigate the existence of Liouville integrable cosmological models in hybrid metric-Palatini theory by using symmetry conditions and conservation laws for the field equations. The exact and analytic solutions of the integrable systems found in this research are presented in terms of quadratics and Laurent expansions.
MODERN PHYSICS LETTERS A
(2021)
Article
Astronomy & Astrophysics
B. Altschul, J. R. Nascimento, A. Yu Petrov, P. J. Porfirio
Summary: This paper investigates the first-order perturbations of Godel-type metrics in the non-dynamical framework. By solving the perturbed field equations, it is found that the first-order field equations break the symmetries of the unperturbed metrics and affect the equilibrium radii of planar geodesic orbits.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Joao Luis Rosa, Francisco S. N. Lobo, Diego Rubiera-Garcia
Summary: This study explores cosmological sudden singularities in the dynamically equivalent scalar-tensor representation of generalized hybrid metric-Palatini gravity. The research shows that sudden singularities may appear in the fourth-order time derivative of the scale factor under certain assumptions, providing constraints on the occurrence of sudden singularities in our universe as measured from the Big Bang.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
J. Sadeghi, S. Noori Gashti, F. Darabi
Summary: In this paper, we investigate the cosmological implications of a hybrid combination of Einstein-Hilbert action with curvature scalar R and a function f (R) in Palatini gravity within the framework of inflationary scenario, based on the Swampland conjecture. We analyze the cosmological quantities and compare them with observational data, such as slow-roll parameter, scalar spectral index (ns), tensor-to-scalar ratio (rs), and assess the compatibility of the model with Planck observations by applying the Swampland conjecture to different plots.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Jaakko Annala, Syksy Rasanen
Summary: We investigate the stability of gravitational theories with arbitrary algebraic dependence on three traces of the Riemann tensor: the Ricci tensor, the co-Ricci tensor, and the homothetic curvature tensor, which we collectively refer to as Ricci-type tensors. We consider both unconstrained connections and cases where either torsion or non-metricity is assumed to vanish. We determine the combinations of Ricci-type tensors that introduce new degrees of freedom around Minkowski and FLRW space and identify the presence of ghosts. We find that only theories with zero torsion and dependence solely on the Ricci tensor have healthy new degrees of freedom, and projective invariance is not sufficient to ensure a ghost-free theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Particles & Fields
J. S. Goncalves, A. F. Santos
Summary: This paper examines the f(R, T, R μνP μν) gravity theory and its implications on causality. The analysis using Godel-type solutions shows that this model allows both causal and non-causal solutions, depending on the content of matter in the universe.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Mathematical
Nisha Godani
Summary: The theory of Hybrid metric-Palatini gravity, proposed in 2012, explains both local and cosmological observations. In this paper, the theory is used to obtain charged traversable wormhole solutions and the results are compared for different cases.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
J. McDonald
Summary: In comparison to the conventional metric formulation, reconsideration of unitarity violation in the electroweak vacuum under the Palatini formulation reveals that Higgs Inflation model does not violate unitarity at low energies. This suggests that Palatini Higgs Inflation may have a significant advantage over metric Higgs Inflation in terms of conservation of unitarity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Angelos Lykkas, Kyriakos Tamvakis
Summary: The study explores an extension of the Palatini-R-2 model by introducing field dependencies to the R-2 coefficient in the form of logarithmic corrections, finding that the predicted values lie in the favored region of observations. The assumed scalar field dependence tends to decrease the value of the spectral index n(s) and potentially increase the tensor-to-scalar ratio r, deviating from the highly suppressed values commonly found in similar models within the same framework.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Konstantinos Dimopoulos, Alexandros Karam, Samuel Sanchez Lopez, Eemeli Tomberg
Summary: We propose a model of quintessential inflation in Palatini R2 gravity, where a scalar field with a simple exponential potential is coupled to gravity with a running non-minimal coupling. By studying the combination of the scalar sector and an ideal fluid, we investigate the cosmological evolution of the model from inflation to dark energy domination. Numerical scan over the parameter space reveals points that align with observations for both the inflationary CMB data and the late-time behavior.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Noelia S. Santos, Janilo Santos
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Astronomy & Astrophysics
Crislane S. Santos, Janilo Santos, Salvatore Capozziello, Jailson S. Alcaniz
GENERAL RELATIVITY AND GRAVITATION
(2017)
Article
Astronomy & Astrophysics
B. Santos, M. Campista, J. Santos, J. S. Alcaniz
ASTRONOMY & ASTROPHYSICS
(2012)
Article
Astronomy & Astrophysics
J. Santos, M. J. Reboucas, J. S. Alcaniz
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2010)
Article
Astronomy & Astrophysics
F. C. Carvalho, E. M. Santos, J. S. Alcaniz, J. Santos
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2008)
Review
Astronomy & Astrophysics
M. J. Reboucas, J. Santos
Article
Astronomy & Astrophysics
J. Santos, M. J. Reboucas, T. B. R. F. Oliveira
Article
Astronomy & Astrophysics
N. Pires, J. Santos, J. S. Alcaniz
Article
Astronomy & Astrophysics
J. Santos, J. S. Alcaniz, F. C. Carvalho, N. Pires
Article
Astronomy & Astrophysics
M. Campista, B. Santos, J. Santos, J. S. Alcaniz
Article
Astronomy & Astrophysics
J. A. S. Lima, J. Santos
Summary: Heat flows from hotter to colder in accordance with the laws of thermodynamics, but the relationship between inertia and weight in general relativity breaks the standard equilibrium condition. The thermal equilibrium condition for a static self-gravitating fluid is heavily dependent on the underlying spacetime geometry, and new equilibrium conditions have been deduced for certain gravity theories. These results suggest that experiments based on heat theory may be used to explore gravity theories and the geometric nature of spacetime structure.
Proceedings Paper
Astronomy & Astrophysics
Janilo Santos, Crislane de Souza Santos
I COSMOSUL: COSMOLOGY AND GRAVITATION IN THE SOUTHERN CONE
(2012)
Article
Education, Scientific Disciplines
Janilo Santos, Bruna P. W. de Oliveira, Osman Rosso Nelson
REVISTA BRASILEIRA DE ENSINO DE FISICA
(2012)
Article
Astronomy & Astrophysics
J. Santos, J. S. Alcaniz, M. J. Reboucas, F. C. Carvalho