Gravitational Constant Research Articles

Abstract We consider a modified gravity model with a running gravitational constant coupled to a varying dark energy fluid and test its imprint on the growth of structure in the universe. Using redshift space distortion (RSD) measurement results, we show a tension at the $$3 \sigma $$ 3 σ level between the best fit $$\Lambda $$ Λ CDM and the corresponding parameters obtained from the Planck data. Unlike many modified gravity-based solutions that overlook scale dependence and model-specific background evolution, we study this problem in the broadest possible context by incorporating both factors into our investigation. We performed a full perturbation analysis to demonstrate a scale dependence in the growth equation. Fixing the scale to $$k = 0.1 h$$ k = 0.1 h Mpc $$^{-1}$$ - 1 and introducing a phenomenological functional form for the varying Newton coupling G with only one free parameter, we conduct a likelihood analysis of the RSD selected data. The analysis reveals that the model can bring the tension level within $$1 \sigma $$ 1 σ while maintaining the deviation of G from Newton’s gravitational constant at the fifth order.

Abstract In the current research article, we delve into the theoretical implications of Rastall–Rainbow Gravity within the framework of modified gravitational theories in which the curvature of spacetime is taken into account during the variation of the gravitational constant. We investigate gravitational decoupling phenomena through the Minimal Deformation Method (MGD), which consists of independent modifications of different matter and energy components under the action of the revised gravitational field equations. We thoroughly outline the roles of these decouplings in physical cosmological measurements, which include spectral properties of distant astrophysical sources and the redshift – distance relation, with particular emphasis on their implications on redshifts. Further, we study the behavior of the four energy conditions to ensure the physical viability of the model, with particular emphasis on the Dominant Energy Condition (DEC). We demonstrate that Rastall–Rainbow Gravity is in agreement with the underlying relativistic energy bounds, especially given the DEC even if this allows for large deformations of the gravitational field. This is a robust framework for studying cosmic dynamics and structure formation.

The article discusses methods for determining the gravitational constant G and factors affecting the accuracy of measuring this fundamental constant. G was determined using two methods and the accuracy of the results obtained was analyzed. The purpose of the article is to analyze the most effective methods for measuring G and to find ways to further improve the accuracy of determining the gravitational constant. The first part of the article provides an overview of the most effective methods for determining the gravitational constant, as well as a comparative analysis to identify systematic discrepancies and possible sources of error. Two main approaches to measurement are described: a method based on the study of the external photoelectric effect, and a resonance method using a Cavendish torsion balance adapted to improve accuracy by simultaneously measuring the acceleration of gravity at the points under study. The features of each method are considered, including their sensitivity to external influences, local gravitational field conditions, and experimental setup parameters. The second part of the article presents the results of experiments performed using the two above-mentioned methods. Particular attention is paid to the correlation between the measured value of G and the characteristics of the local gravitational background. Based on the data obtained, an assumption was made about a possible dependence of the gravitational constant value on the configuration and intensity of the local gravitational field. A conclusion was made about the need to revise traditional methods of measuring G, with an emphasis on developing new experimental schemes that can take into account the influence of local gravity and minimize the influence of unaccounted factors. The importance of an integrated approach, which involves the simultaneous determination of gravity and the gravitational constant, is emphasized, which can increase the reliability and consistency of the results obtained.

In this paper, we investigate slow-roll inflationary scenarios within modified gravity frameworks featuring nonminimal couplings between geometry and a scalar field (the inflaton, [Formula: see text]). Specifically, we consider a generalized gravity model of the form [Formula: see text], where [Formula: see text] and G is Newton’s gravitational constant. In addition to the standard R and [Formula: see text] contributions — where [Formula: see text] is the trace of the energy–momentum tensor — we introduce a nonminimal coupling term [Formula: see text], which modifies the gravitational dynamics and significantly affects the inflationary evolution. We analyze the inflationary behavior under two types of scalar potentials: (i) [Formula: see text] and (ii) [Formula: see text]. By exploring a range of potential parameters, we constrain the modified gravity coefficients [Formula: see text], [Formula: see text] and [Formula: see text] in three configurations: (i) [Formula: see text], [Formula: see text]; (ii) [Formula: see text], [Formula: see text], [Formula: see text]; (iii) [Formula: see text], [Formula: see text], [Formula: see text]. Our results show that incorporating [Formula: see text] term improves the theoretical predictions for both the scalar spectral index [Formula: see text] and the tensor-to-scalar ratio r, leading to better agreement of the considered potentials with recent observational constraints.

This paper explores the relationships between the fundamental constants of physics, which are electron rest mass, Planck's constant, speed of light, vacuum permittivity, elementary charge, classical electron radius, and gravitational constant.

Diameter measurement of silicon sphere at nanometer level with laser interferometry in measurement of gravitational constant

We delve into the topology and morphology of the emergent time that arises from a electrons kinetic cloud virtually confined in a toroidal shape due to high-opacity environments. Different results using the most usual opacity models are shown. We analyze the dynamics that best represent such complexity, especially for stellar environments, focusing on the inner, mid and outer zones of the radiative layer. Detailed results of the expected induced Gravity, including their values and the time needed to be conserved over cosmological Time are shown. Then we extrapolate the results of the Gravity induced by the emergent time for different types of stars in function of their percentage per size and by mass, infering that the 95% of the Gravity created in the stars ranges from -43% till 19% of the emergent gravity arised in Sun-like stars. Finally we show how the variabilty of the gravitational constant could be demonstrated by experiments carried out on the Earth itself and how a new discipline “PaleoGravity” based on them could help us to study the origin of any chemical element present on Earth, the solar system and even asteroids.

The recent observational evidence of deviations from the Lambda cold dark matter model points toward the presence of evolving dark energy. The simplest possibility consists of a cosmological scalar field φ, dubbed “quintessence,” driving the accelerated expansion. We assess the evidence for the existence of such a scalar field. We find that, if the accelerated expansion is driven by quintessence, the data favor a potential energy V(φ) that is concave, i.e., m2=d2V/dφ2<0. Furthermore, and more significantly, the data strongly favor a scalar field that is nonminimally coupled to gravity [Bayes factor log(B)=7.34±0.6], leading to time variations in the gravitational constant on cosmological scales, and the existence of fifth forces on smaller scales. The fact that we do not observe such fifth forces implies that new physics must come into play on noncosmological scales that quintessence is an unlikely explanation for the observed cosmic acceleration.

We investigate potential singularities in isotropic cosmological models featuring a time-varying speed of light and the gravitational constant. The governing field equations generally simplify into two-dimensional systems, subject to analysis through dynamical systems techniques within phase space and the application of asymptotic splitting methods. In the broader context, our findings reveal the existence of initially expanding closed models that undergo subsequent recollapse towards a future singularity, and open universes exhibiting perpetual expansion into the future. The specific characteristics of these singularities are also expounded upon.

We compute the conservative and radiation-reaction contributions to classical observables in the gravitational scattering between a spinning and a spinless black hole to the fourth order in spin and third order in the gravitational constant. The conservative results are obtained from two-loop amplitudes for the scattering process of a massive scalar with a massive spin-s field (s=0, 1, 2) minimally coupled to gravity, employing the recently introduced spin interpolation method to resolve all spin-Casimir terms. The two-loop amplitude exhibits a spin-shift symmetry in both probe limits, which we conjecture to be a sign of yet unknown integrability of Kerr orbits through the quartic order in spin and to all orders in the gravitational constant. We obtain the radial action from the finite part of the amplitude and use it to compute classical observables, including the impulse and spin kick. This is done using the recently introduced covariant Dirac brackets, which allow for the computation of classical scattering observables for general (nonaligned) spin configurations. Finally, employing the radiation-reaction amplitude proposed by Alessio and Di Vecchia, together with the Dirac brackets, we obtain radiation-reaction contributions to observables at all orders in spin and beyond the aligned-spin limit. We find agreement with known results up to the quadratic order in spin for both conservative and radiation-reaction contributions. Our results advance the state of the art in the understanding of spinning binary dynamics in general relativity and demonstrate the power and simplicity of the Dirac bracket formalism for relating scattering amplitudes to classical observables.

In this study, we consider FRW universe filled with matter, non-minimally coupling (NMC) scalar field under V(ϕ)=V0ϕ2 potential and holographic vacuum energy. Dark energy is contributed from both holographic vacuum energy and the NMC scalar field. NMC effective gravitational constant Geff(ϕ), is naturally defined at the action level. Therefore, the gravitational constant in the holographic vacuum density is an effective one, i.e. ρΛ=3c2/8πGeffL2. Apparent horizon is chosen as IR holographic cutoff scale as it is a trapped null surface. There are nine fixed points in this dynamical system with four independent dimensionless parameters. We consider flat case and find that viable cosmological evolution follows the sequence: an initial stiff-fluid-dominated phase, transitioning through a nearly dust-dominated era, and eventually reaching a stable dark energy-dominating state. Stability analysis requires that ξ<0 and 0<c<1 for the theory to be physically valid. Since zero NMC coupling, ξ=0, is not allowed in the autonomous system, the model can not completely recover canonical scalar field case. That is to say, as ξ→0- and c→0+, the model can only approach the canonical scalar case but can not completely recover it. To approach dust or stiff fluid dominations, both magnitudes of the NMC coupling and the holographic parameter must be small. Numerical integration shows that for any allowed values of ξ and c, weff approaches -1 at late times. Increasing of c does not change shape of the weff, but larger c increases weff. As ξ becomes stronger, dust era gradually disappears. Good behaviors of the dynamics require -1≪ξ<0 and 0<c≪1.

Considering the Einstein-Hilbert truncation for the running action in (Euclidean) quantum gravity, we derive the renormalization group equations for the cosmological and Newton constant. We find that these equations admit only the Gaussian fixed point with a UV-attractive and a UV-repulsive eigendirection, and that there is no sign of the nontrivial UV-attractive fixed point of the asymptotic safety scenario. Crucial to our analysis is a careful treatment of the measure in the path integral that defines the running action and a proper introduction of the physical running scale k. We also show why and how in usual implementations of the RG equations the aforementioned UV-attractive fixed point is generated.

Testing black holes with cosmological constant in Einstein-bumblebee gravity through the black hole shadow using EHT data and deflection angle

The article presents an original model regarding the fine structure of matter. Currently, the intimate structure of matter is studied by fragmenting subatomic particles in particle accelerators and analyzing the physical entities resulting from this action. This article explores the existence of an alternative model which approaches the study of matter starting from the photon, the smallest material entity. The model is based on the numerical values of fundamental physical constants such as the speed of light, the gravitational constant, the Planck constant, the Avogadro number, and the fine structure constant. Finally, a model regarding the generation of the proton mass based on the relationships established in the article is proposed.

Satellite galaxies endure powerful environmental tidal forces that drive mass stripping of their outer regions. Consequently, satellites located in central regions of galaxy clusters or groups, where the tidal field is strongest, are expected to retain their central dense regions while losing their outskirts. This process produces a spatial segregation in the mean mass density with the cluster-centric distance (the bar ρ -r relation). To test this hypothesis, we combined semi-analytical satellite orbital models with cosmological galaxy simulations. We find that not only the mean total mass densities ( but also the mean stellar mass densities ρ ⋆ ) of satellites exhibit this distance-dependent segregation (bar ρ ⋆ !!-!r). The correlation traces the host's tidal field out to a characteristic transition radius at Rr!≈!0.5 beyond which the satellite population's density profile can have a slight increase or remain flat, reflecting the weakened tidal influence in the outskirts of galaxy clusters and beyond. We compare these predictions with observational data from satellites in the Virgo and Fornax galaxy clusters, as well as the Andromeda and Milky Way systems. Consistent trends in the satellite mean stellar mass densities are observed across these environments. Furthermore, the transition radius serves as a photometric diagnostic tool: it identifies regions where the stellar components of satellites underwent significant tidal processing and probes the gravitational field strength of the host halo.

We present a theory showing the electromagnetic origin of the (“conventional”) Gravity based on some models that demonstrate the close relationship between electromagnetic radiation, matter and Gravity. We also show how Gravity has evolved over Time and the different stages that it has gone through to reach its current state. We also analyze the consequences for the Relativity Theory and the gravitational constant, as well as the future of Gravity and consequently of the Universe.

Considering (Euclidean) quantum gravity in the Einstein-Hilbert truncation, we calculate the one-loop effective action Γgrav1l using a spherical background. Usually, this calculation is performed resorting to proper-time regularization within the heat kernel expansion and gives rise to quartically and quadratically UV-sensitive contributions to the vacuum energy ρvac=Λcc8πG, with Λcc and G cosmological and Newton constant, respectively. We show that, if the measure in the path integral that defines Γgrav1l is correctly taken into account, and the physical UV cutoff Λcut properly introduced, ρvac presents only a (mild) logarithmic sensitivity to Λcut. We also consider a free scalar field and a free Dirac field on a spherical gravitational background and find that the same holds true even in the presence of matter. These results are found without resorting to any supersymmetric embedding of the theory and shed new light on the cosmological constant problem. Published by the American Physical Society 2025

We study a two-fluid cosmological model in the context of a dynamical Chern–Simons modified massive gravity with a time-varying gravitation predicted from recent astronomical observations. The solutions of the Friedmann equation are hyperbolically characterized by a cosmic transition from deceleration to acceleration and a jerk parameter which tends toward unity at late times. We have discussed two independent cases characterized by both hyperbolic evolution of the scale factor and graviton mass [Formula: see text][Formula: see text]eV. Both models predict a very slow evolution of the gravitational constant and the crossing of the phantom-divide line. Confrontations with various recent astronomical observations including BBN+PP+BAO+SHOES data sets have been done to estimate the parameters of the model.

Emergent cosmological model from running Newton constant

The Moon's gravitational field strength (17% Earth's gravity) may facilitate the use of bodyweight jumping as an exercise countermeasure against musculoskeletal and cardiovascular deconditioning in reduced gravity settings. The present study characterised the acute physiological and kinetic responses to bodyweight jumping in simulated Lunar gravity. Nineteen healthy adults (age: 25±7years, weight: 73±11kg; height: 1.81±0.05m, : 50±11mLkg-1min-1) performed an incremental jumping test in simulated Lunar gravity (9.5° head-up tilt suspension) comprising 4-min stages of jumping with 1-min rests, beginning at 30cm and increasing 5cm per stage up to 70cm. A graded exercise test (GXT) to volitional exhaustion was subsequently performed using upright cycle ergometry. Cardiorespiratory outcomes ( , , , breathing frequency, respiratory exchange ratio and heart rate (HR)) and peak vertical ground reaction forces (vGRF) increased linearly (R2=0.77-0.97) and blood lactate concentrations increased exponentially with jump height (R2=0.98). Participants achieved HRs of 158±17beatsmin-1 (88±9% HRmax), metabolic rates of 35±6mLkg-1min-1 (71±9% ), blood lactate concentrations of 5.8±1.7mmolL-1 and peak vGRFs of 119±17% bodyweight. Jumping at ∼20% bodyweight requires no equipment, allows for submaximal cardiovascular exercise intensities with and without blood lactate accumulation, and may have value as an exercise countermeasure in Lunar/Martian surface habitats.