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The starting point of this work is the original Einstein action, sometimes called the Gamma squared action. Continuing from our previous results, we study various modified theories of gravity following the Palatini approach. The metric and…

General Relativity and Quantum Cosmology · Physics 2023-09-29 Christian G. Boehmer , Erik Jensko

Gravity is derived from an entropic action coupling matter fields with geometry. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of an renormalizable effective density matrix and…

General Relativity and Quantum Cosmology · Physics 2025-03-20 Ginestra Bianconi

The presently open problem of the Hubble tension is shown to be removed in the context of a modified theory of gravity with a non-minimal coupling between curvature and matter. By evolving the cosmological parameters that match the cosmic…

General Relativity and Quantum Cosmology · Physics 2024-10-22 Miguel Barroso Varela , Orfeu Bertolami

A new class of gravity-matter models defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold are studied in some detail. These models involve…

General Relativity and Quantum Cosmology · Physics 2015-06-22 Eduardo Guendelman , Ramón Herrera , Pedro Labraña , Emil Nissimov , Svetlana Pacheva

We present a theory of modified gravity, inspired by the gauge theories, where the commutator algebra of covariant derivative gives us an added term with respect to the General Relativity, which represents the interaction of gravity with a…

General Relativity and Quantum Cosmology · Physics 2012-01-05 M. Hamani Daouda , Manuel E. Rodrigues , M. J. S. Houndjo

We show that the use of suitable theorems for black hole formation in Friedmann expanding universes leads to a modification of the Bekenstein-Hawking entropy. By adopting an argument similar to the original Bekenstein one, we write down the…

High Energy Physics - Theory · Physics 2014-05-29 Stefano Viaggiu

We forecast the constraints on both Hu-Sawicki model and Bertschinger-Zukin model of modified gravity within the Parameterized Post-Friedmann (PPF) formalism for the Planck satellite experiment by performing the joint analysis of…

Cosmology and Nongalactic Astrophysics · Physics 2013-08-09 Bin Hu , Michele Liguori , Nicola Bartolo , Sabino Matarrese

By considering matter as a constraint on the availability of gravitational degrees of freedom and accounting for the statistical interpretation of Rindler horizons, the freedom to construct quantum gravity theories reproducing General…

General Physics · Physics 2019-01-25 P. A. Mandrin

With the increasing wealth of high-quality astronomical and cosmological data and the manifold departures from General Relativity in principle conceivable, the development of generalized parametrization frameworks that unify gravitational…

Cosmology and Nongalactic Astrophysics · Physics 2019-08-22 Lucas Lombriser

In this paper we demonstrate that Boltzmann's $H$-theorem does not necessarily hold in the context of theories of gravity with nonminimally coupled matter fields. We find sufficient conditions for the violation of Boltzmann's $H$-theorem…

General Relativity and Quantum Cosmology · Physics 2020-07-29 P. P. Avelino , R. P. L. Azevedo

A covariant Hamiltonian description of Palatini's gravity on manifolds with boundary is presented. Palatini's gravity appears as a gauge theory satisfying a constraint in a certain topological limit. This approach allows the consideration…

Mathematical Physics · Physics 2016-05-12 Alberto Ibort , Amelia Spivak

We present a comparative analysis of the plethora of nonextensive and/or nonadditive entropies which go beyond the standard Boltzmann-Gibbs formulation. After defining the basic notions of additivity, extensivity, and composability, we…

General Relativity and Quantum Cosmology · Physics 2024-09-30 Mariusz P. Dabrowski

A coarse-graining of spin networks is expressed in terms of partial tracing, thus allowing to use tools of quantum information theory. This is illustrated by the analysis of a simple black hole model, where the logarithmic correction of the…

General Relativity and Quantum Cosmology · Physics 2015-06-25 Daniel R. Terno

We present a resum\'e on the modified theory of gravity, called pseudo-complex General Relativity (pc-GR). It is the second in a series of papers, where the first one (Boller et al. 2019, referred to as paper I) discussed the observational…

Astrophysics of Galaxies · Physics 2019-04-10 P. O. Hess , Th. Boller , A. Mueller , H. Stoecker

We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $\phi$ and the trace of the energy momentum tensor $T$ as $f(\phi,T) = 2 \phi( \kappa^{1/2} \alpha T + \kappa^{5/2} \beta…

General Relativity and Quantum Cosmology · Physics 2022-10-17 Ashmita , Payel Sarkar , Prasanta Kumar Das

A set of 3+1 equations for stochastic inflation incorporating all metric and scalar matter degrees of freedom, first presented in previous work, are re-derived in a gauge invariant manner. We then present numerical implementations of these…

General Relativity and Quantum Cosmology · Physics 2026-05-04 Yoann L. Launay , Gerasimos I. Rigopoulos , E. Paul S. Shellard

We present a coherent picture of the quantum mechanics of black holes. The picture does not require the introduction of any drastically new physical effect beyond what is already known; it arises mostly from synthesizing and…

High Energy Physics - Theory · Physics 2015-06-19 Yasunori Nomura , Sean J. Weinberg

We derive a formula for the nonequilibrium entropy of a classical stochastic field in terms of correlation functions of this field. The formalism is then applied to define the entropy of gravitational perturbations (both gravitational waves…

General Relativity and Quantum Cosmology · Physics 2009-10-22 R. Brandenberger , T. Prokopec , V. Mukhanov

The field equations of a generalized $f(R)$ type gravity model, in which there is an arbitrary coupling between matter and geometry, are obtained. The equations of motion for test particles are derived from a variational principle in the…

General Relativity and Quantum Cosmology · Physics 2009-05-26 T. Harko

A calculation by Jacobson [1] strongly implies that the field equations which describe gravity are emergent phenomena. In this paper, the method is extended to the case of a non-commutative spacetime. By making use of a non-commutative…

High Energy Physics - Theory · Physics 2015-05-21 Simon Moolman