New theory of gravity
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New Theories of Gravity: An Overview
Introduction to Extended Theories of Gravity
Extended Theories of Gravity aim to address the limitations of General Relativity (GR) at both infrared and ultraviolet scales. These theories seek to preserve the successful predictions of Einstein's theory while resolving emerging conceptual and experimental issues in astrophysics, cosmology, and high-energy physics. They aim to provide a self-consistent framework to tackle problems such as inflation, dark energy, dark matter, and large-scale structure, and to offer an effective description of Quantum Gravity.
New Relativistic Theories of Gravity
A new relativistic theory of gravity has been proposed that aligns with all current experimental data. This theory is metric-based, Lagrangian-based, and features a preferred frame with conformally flat space slices. With appropriate choices of functions, parameters, and cosmological models, this theory matches the post-Newtonian limit of General Relativity.
New General Relativity and Torsion
New General Relativity is formulated on Weitzenböck space-time, characterized by a vanishing curvature tensor and a torsion tensor formed by four parallel vector fields. This theory, which includes parameters beyond the Einstein constant, agrees with all experimental data to date. It provides solutions such as the Schwarzschild metric for static, spherically symmetric gravitational fields and predicts the existence of an antisymmetric field of zero mass and spin in the weak-field approximation.
Nonsymmetric Field Structure in Gravity
Another new theory of gravity proposes that the geometry of space-time is determined by a nonsymmetric field structure. This theory adheres to general covariance, the weak principle of equivalence, and derives field equations from a Lagrangian action principle. It agrees with classical tests of General Relativity but predicts significant deviations for compact sources or supermassive stars, preventing the formation of black holes as predicted by Einstein's theory.
Effective Field Theories in Post-Newtonian Gravity
Effective Field Theories (EFTs) have been introduced into post-Newtonian gravity to study gravitational waves from compact binary inspirals. This interdisciplinary approach has linked quantum field theory and classical gravity, providing a robust methodology for advancing post-Newtonian theory. EFTs offer a universal framework that enhances our understanding of gravitational waves and the fundamental principles of gauge and gravity theories.
Einstein-Gauss-Bonnet Gravity in Four Dimensions
A modified theory of gravity in four-dimensional spacetime, known as Einstein-Gauss-Bonnet gravity, has been developed. This theory includes the Einstein-Hilbert term with a cosmological constant and the Gauss-Bonnet term, which contributes to gravitational dynamics while preserving the number of graviton degrees of freedom. It predicts new corrections to the dispersion relation of cosmological tensor and scalar modes and resolves singularities in spherically symmetric solutions.
Modified Gravity and Cosmology
Recent work on modified theories of gravity has explored various models, including scalar-tensor, Einstein-aether, Bimetric theories, and others. These theories have been motivated by advances in observational cosmology, allowing precision tests of fundamental physics on a universal scale. The Parameterised Post-Friedmannian formalism has been developed to constrain deviations from General Relativity in cosmology.
New Approaches to Modifying Gravity
Inspired by Continuum Mechanics, new gravitational actions for modified theories of gravity have been formulated. These models are natural generalizations of existing theories and possess interesting properties that can be experimentally determined.
Quantum Gravity Experiments
Recent advances in quantum experiments have opened new possibilities for probing relativistic effects of gravity on quantum properties. Using the framework of Quantum Field Theory in Curved Spacetime (QFTCS), these experiments could enhance measurements of gravitational effects, such as gravitational waves, providing direct validation of quantum gravity predictions.
Parametrized Post-Einsteinian Gravitational Waveforms
Gravitational wave observations have enabled tests of modified theories of gravity in the strong-field regime. The parameterized post-Einsteinian formalism introduces generic parameters to capture non-Einsteinian effects in gravitational waveforms. This approach allows for efficient testing of various modified theories of gravity against observed data.
Conclusion
The exploration of new theories of gravity is a dynamic and evolving field, driven by the need to address the limitations of General Relativity and to unify it with quantum mechanics. These theories offer promising avenues for understanding the fundamental nature of gravity and the universe.
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