Searches for beyond-Riemann gravity

Kostelecky, Alan; Li, Zonghao

doi:10.48550/arxiv.2106.11293

Cited by 4 publications

(5 citation statements)

References 91 publications

(202 reference statements)

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“…Some experimental constraints on background field coefficients such as those obtained in, e.g., refs. [30,31] are interpreted as bounds on explicit diffeomorphism violation. The data tables [32] can be consulted as an extensive compilation of such constraints.…”

Section: Introductionmentioning

confidence: 99%

Modified-gravity theories with nondynamical background fields

Reyes,

Schreck

2022

Preprint

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We study the dynamics of a modified-gravity theory, which is supplemented by an extended Gibbons-Hawking-York boundary term and incorporates diffeomorphism violation through nondynamical background fields denoted as u and s µν in the literature. An ADM decomposition allows us to project the modified Einstein equations into purely spacelike hypersurfaces, which implies the field equations for the induced dynamical three-metric. We also obtain the Hamilton-Jacobi equations of motion for the canonical variables of the theory based on its Hamiltonian, which was derived in a previous work. The computations show that the dynamical field equations obtained from the Lagrangian and Hamiltonian approaches are consistent with each other. Connections to Brans-Dicke theory and ghost-free massive gravity are established.

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Section: Introductionmentioning

confidence: 99%

Modified-gravity theories with nondynamical background fields

Reyes,

Schreck

2022

Preprint

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“…In the context of explicit symmetry violation, both phenomena are not directly linked to each other, but must be considered as different manifestations of physics beyond GR. The recent papers [100,101] ex-tensively complement the very first work [99], which introduced the gravitational sector of the SME more than 15 years ago.…”

Section: Introductionmentioning

confidence: 77%

Hubble tension as a guide for refining the early Universe: Cosmologies with explicit local Lorentz and diffeomorphism violation

Khodadi¹,

Schreck²

2023

Preprint

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This paper is dedicated to assessing modified cosmological settings based on the gravitational Standard-Model Extension (SME). Our analysis rests upon the Hubble tension (HT), which is a discrepancy between the observational determination of the Hubble parameter via data from the Cosmic Microwave Background (CMB) and Type Ia supernovae, respectively. While the latter approach is model-independent, the former highly depends on the model used to describe the physics of the early Universe. Motivated by the HT, we take into account two recently introduced cosmological models as test frameworks of the pre-CMB era. These settings involve local Lorentz and diffeomorphism violation parameterized by nondynamical SME background fields s 00 and s ij , respectively. We aim at explaining the tension in the measured results of the cosmic expansion rate in early and late epochs by resorting to these two modified cosmologies as potential descriptions of the pre-CMB era. As long as the HT does not turn out to be a merely systematic effect, it can serve as a criterion for exploring regions of the parameter space in certain pre-CMB new-physics candidates such as SME cosmologies. By setting extracted limits on SME coefficients into perspective with already existing bounds in the literature, we infer that none of the aforementioned models are suitable pre-CMB candidates for fixing the HT. In this way, new physics arising from the particular realizations of Lorentz and diffeomorphism violation studied in this article does not explain the HT. Our paper exemplifies how to exploit this discrepancy as a novel possibility of refining our description of the early Universe.

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“…In terms of the four field variables N , λ 1 , λ 2 , λ 3 and the four parameters β 1 , β 2 , β 3 , β 4 , the solutions are governed by the potential U(Y) given in Eq. (28). We explicitly determine and classify the solutions with vanishing curvatures for the dynamical and fiducial metrics, proving that they are either Lorentz invariant or break four of the six generators of the Lorentz group.…”

Section: B Propagatormentioning

confidence: 96%

“…Note that in contrast no fluctuations are associated with the nondynamical fiducial metric f µν in the action (1), where the Lorentz breaking is explicit. The phenomenology of explicit breaking without fluctuations can be explored in gravitational effective field theory [28].…”

Section: B Spacetime Symmetriesmentioning

confidence: 99%

Lorentz symmetry in ghost-free massive gravity

Kostelecký¹,

Potting²

2021

Preprint

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The role of Lorentz symmetry in ghost-free massive gravity is studied, emphasizing features emerging in approximately Minkowski spacetime. The static extrema and saddle points of the potential are determined and their Lorentz properties identified. Solutions preserving Lorentz invariance and ones breaking four of the six Lorentz generators are constructed. Locally, globally, and absolutely stable Lorentz-invariant extrema are found to exist for certain parameter ranges of the potential. Gravitational waves in the linearized theory are investigated. Deviations of the fiducial metric from the Minkowski metric are shown to lead to pentarefringence of the five wave polarizations, which can include superluminal modes and subluminal modes with negative energies in certain observer frames. The Newton limit of ghost-free massive gravity is explored. The propagator is constructed and used to obtain the gravitational potential energy between two point masses. The result extends the Fierz-Pauli limit to include corrections generically breaking both rotation and boost invariance.

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Searches for beyond-Riemann gravity

Cited by 4 publications

References 91 publications

Modified-gravity theories with nondynamical background fields

Modified-gravity theories with nondynamical background fields

Hubble tension as a guide for refining the early Universe: Cosmologies with explicit local Lorentz and diffeomorphism violation

Lorentz symmetry in ghost-free massive gravity

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