Brans-Dicke Research Articles

Screening mechanism and late-time cosmology: Role of a Chameleon–Brans–Dicke scalar field

ABSTRACT We discuss a way in which the geometric scalar field in a Brans–Dicke (BD) theory can evade local astronomical tests and act as a driver of the late-time cosmic acceleration. This requires a self-interaction of the BD scalar as well as an interaction with ordinary matter. The scalar field in this construct acquires a density-dependent effective mass much like a Chameleon field. We discuss the viability of this setup in the context of Equivalence Principle, Fifth Force, and Solar System tests. The cosmological consistency is adjudged in comparison with observational data from recalibrated light curves of type Ia supernova (JLA), the Hubble parameter measurements (OHD) and the Baryon Acoustic Oscillation (BAO). We deduct that the astrophysical constraints indeed favour the existence of a mild scalar-matter interaction in the Jordan Frame.

Analysis of generalized ghost dark energy and new holographic dark energy in Chameleon Brans–Dicke theory

In this work, we discuss the stability analysis of generalized ghost dark energy (GGDE) and new holographic dark energy (NHDE) in the framework of Chameleon Brans–Dicke (CBD) gravity. The adiabatic squared sound speed [Formula: see text] plays a crucial role to analyze the stability of the models. We know that the models are stable if [Formula: see text] and unstable if [Formula: see text]. We study the interacting and noninteracting versions of GGDE and NHDE with dark matter in CBD model in a nonflat FLRW universe. We also try to show that in all cases of investigation, the models are classically stable with suitable choices of parameters. Finally, we analyze the perturbative analysis for both GGDE and NHDE models in the background of CBD gravity.

Stealth metastable state of scalar-tensor thermodynamics

We investigate a puzzle in the recent thermodynamics of scalar-tensor gravity, in which general relativity is a zero-temperature state of equilibrium and scalar-tensor gravity is the non-equilibrium configuration of an effective dissipative fluid. A stealth solution of Brans-Dicke gravity with constant positive temperature is shown to be analogous to a metastable state for the effective fluid and to suffer from an instability. The stability analysis employs a version of the Bardeen-Ellis-Bruni-Hwang gauge-invariant formalism for cosmological perturbations adapted to modified gravity. The metastable state is destroyed by tensor perturbations.

Dark matter and dark energy from a Kaluza–Klein inspired Brans–Dicke gravity with barotropic fluid

We study the Kaluza–Klein inspired Brans–Dicke model with barotropic matter. Following from our previous work, the traditional Kaluza–Klein gravity action is introduced with an additional scalar field and 2 gauge fields. The compactification process results in a Brans–Dicke model with a dilaton coupled to the tower of scalar fields whereas a gauge field from 5-dimensional metric forms a set of mutually orthogonal vectors with 2 additional gauge fields. The barotropic matter is then introduced to complete a realistic set up. To demonstrate the analytical solutions of the model, we consider the case in which only 2 lowest modes becoming relevant for physics at low scale. After derivation, equations of motion and Einstein field equations form a set of autonomous system. The dynamical system is analysed to obtain various critical points. Interestingly, by only inclusion of barotropic matter, the model provides us the critical points which capable of determining the presences of dark matter, dark energy and phantom dark energy.

Constraining Brans–Dicke Cosmology with the CSST Galaxy Clustering Spectroscopic Survey

The Brans–Dicke (BD) theory is the simplest Scalar-Tensor theory of gravity, which can be considered as a candidate of modified Einstein’s theory of general relativity. In this work, we forecast the constraints on BD theory in the CSST galaxy clustering spectroscopic survey with a magnitude limit ∼23 AB mag for point-source 5σ detection. We generate mock data based on the zCOSMOS catalog and consider the observational and instrumental effects of the CSST spectroscopic survey. We predict galaxy power spectra in the BD theory from z = 0 to 1.5, and the galaxy bias and other systematical parameters are also included. The Markov Chain Monte Carlo technique is employed to find the best-fits and probability distributions of the cosmological and systematical parameters. A BD parameter ζ is introduced, which satisfies . We find that the CSST spectroscopic galaxy clustering survey can give ∣ζ∣ < 10−2, or equivalently and , under the assumption ζ = 0. These constraints are almost at the same order of magnitude compared to the joint constraints using the current cosmic microwave background, baryon acoustic oscillations and Type Ia supernova data, indicating that the CSST galaxy clustering spectroscopic survey would be powerful for constraining the BD theory and other modified gravity theories.

Shadows in conformally related gravity theories

Null geodesics are invariant under a conformal transformation, and thus it might seem natural to assume that the observables corresponding to the shadow of a space-time are also conformally invariant. Here, we argue instead, that since the Arnowitt-Deser-Misner mass and the active gravitational mass of an asymptotically flat space-time are not, in general, invariant under such conformal transformations, the shadow radius for photon motion in a space-time would be quantitatively different, when viewed from two different conformally related frames, although the expression for the shadow radius is similar. We then use this fact to propose a novel method to constrain the relevant parameters in a gravity theory conformally related to general relativity. As examples of our method, we constrain the parameter space in Brans-Dicke theory, and a class of brane-world gravity models, by using the recent observational data of M87⁎ by the Event Horizon Telescope.

A Swinging Rod in Brans‐Dicke Theory

AbstractThis article presents the calculation of gravitational radiation from an oscillating rod in Brans–Dicke (BD) theory. Here only the selected formulae is shown and is applied to a toy problem without any rigorous derivation. First, the explicit expressions for the polarizations are calculated and then the power radiated away in gravitational waves (GWs) is obtained. This problem is motivated by the famous Eddington's spinning rod.

Study of axially symmetric viscous Ricci dark energy model in Brans–Dicke theory

In this paper, we have investigated axially symmetric and anisotropic space–time filled with viscous Ricci dark energy and pressure-less dark matter in the frame-work of Brans–Dicke(BD) theory of gravitation. To solve the field equations, we use the following conditions: (i) the relationship between metric potentials which is obtained from the condition that shear scalar of the model is directly proportional to the expansion scalar, (ii) the average scale factor varies with time as a(t)=[sinh(αt)]1k, and (iii) the bulk viscous coefficient (ξ) as ξ=ξ0+ξ1h+ξ2h′′, where ξ0, ξ1 and ξ2 are constants and h=HH0. We have studied the cosmological parameters, like bulk viscosity coefficient (ξ), effective equation of state (ωeft), deceleration (q), Om diagnostic and cosmological planes like state-finder diagnostics {r,s} and {r,q} planes. And also, we have analyzed the physical behavior of these parameters through pictorial representation. The deceleration and effective equation of state parameters are very close to recent observational data in our model.

Jordan and Einstein frames from the perspective of ω=−3/2 Hamiltonian Brans-Dicke theory

We carefully perform a Hamiltonian Dirac's constraint analysis of the $\ensuremath{\omega}=\ensuremath{-}\frac{3}{2}$ Brans-Dicke theory with the Gibbons-Hawking-York boundary term. The Poisson brackets are computed via functional derivatives. After a brief summary of the results for the $\ensuremath{\omega}\ensuremath{\ne}\ensuremath{-}\frac{3}{2}$ case [G. Gionti S. J., Canonical analysis of Brans-Dicke theory addresses Hamiltonian inequivalence between the Jordan and Einstein frames, Phys. Rev. D 103, 024022 (2021)] we derive all Hamiltonian Dirac's constraints and constraint algebra in both the Jordan and the Einstein frames. Confronting and contrasting Dirac's constraint algebra in both frames, it is shown that they are not equivalent. This highlights that the transformations from the Jordan to the Einstein frames are not Hamiltonian canonical transformations.

FRW cosmological models with Barrow holographic dark energy in Brans–Dicke theory

In this paper, we have generalized the behaviors of transit cosmological model under the observational data with Barrow holographic dark energy. We consider the scale factor field as [Formula: see text] to get exact solutions for the field equations in a non-flat FRW universe in Brans–Dicke theory. The values of the model parameters [Formula: see text] and [Formula: see text] are obtained by best fitting of 46 observational Hubble data (OHD) points in the range [Formula: see text]. The derived model exhibits a transition scenario for open, flat and closed universe. The EoS parameter shows a quintom-like behavior, lies both quintessence ([Formula: see text]) and phantom ([Formula: see text]) regions and crosses the phantom divide. The matter and dark energy density parameters [Formula: see text], scalar field [Formula: see text] and other cosmological parameters provide the results consistent with the recent observational datasets. Some other physical and geometrical behaviors of BHDE are also described and the satisfactory behaviors are found with current observations (OHD+JLA).

Conserved charges in Chern-Simons modified theory and memory effects

In this work, conserved charges and fluxes at the future null infinity are determined in the asymptotically flat spacetime for Chern-Simons modified gravity. The flux-balance laws are used to constrain the memory effects. For tensor memories, the Penrose's conformal completion method is used to analyze the asymptotic structures and asymptotic symmetries, and then, conserved charges for the Bondi-Metzner-Sachs algebra are constructed with the Wald-Zoupas formalism. These charges take very similar forms to those in Brans-Dicke theory. For the scalar memory, Chern-Simons modified gravity is rewritten in the first-order formalism, and the scalar field is replaced by a 2-form field dual to it. With this dual formalism, the scalar memory is described by the vacuum transition induced by the large gauge transformation of the 2-form field.

Isotropic and complexity-free deformed solutions in self-interacting Brans–Dicke gravity

In this work, we focus on constructing two analogs of an anisotropic seed solution via the decoupling technique. For this purpose, we add a new matter source alongside the anisotropic fluid in a static sphere. A transformation in the radial metric component is applied to split the field equations into two sets such that the influence of each source is limited to one array. The anisotropic solution constructed by employing the embedding class-one condition is used to specify the set corresponding to the seed source. We obtain two solutions of the second set (related to the additional source) by applying constraints on the anisotropy and complexity of the self-gravitating system. A smooth junction between the interior and exterior spacetimes determines the unknown constants. Various physical characteristics, such as viability and stability, are graphically analyzed by utilizing the radius and mass of the star PSR J1614-2230. It is found that the extended solutions agree with the energy conditions as well as stability criteria for selected values of the parameters.

Exploring physical features of anisotropic quark stars in Brans-Dicke theory with a massive scalar field via embedding approach * *Supported by the Postdoctoral Fellowship at Zhejiang Normal University (ZC304022919)

The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with the Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, and EXO1785-248, are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of the mass of scalar field , coupling parameter , and bag constant on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions and necessary stability criteria under the influence of a gravitational scalar field.

Quantum scale invariant gravity in the de Donder gauge

We perform the manifestly covariant quantization of a scale invariant gravity with a scalar field, which is equivalent to the well-known Brans-Dicke gravity via a field redefinition of the scalar field, in the de Donder gauge condition (or harmonic gauge condition) for general coordinate invariance. First, without specifying the expression of a gravitational theory, we write down various equal-time (anti-)commutation relations (ETCRs), in particular, those involving the Nakanishi-Lautrup field, the FP ghost, and the FP antighost only on the basis of the de Donder gauge condition. It is shown that choral symmetry, which is a Poincar${\rm{\acute{e}}}$-like $IOSp(8|8)$ supersymmetry, can be derived from such a general action with the de Donder gauge. Next, taking the scale invariant gravity with a scalar field as a classical theory, we derive the ETCRs for the gravitational sector involving the metric tensor and scalar fields. Moreover, we account for how scale symmetry is spontaneously broken in quantum gravity, thereby showing that the dilaton is a massless Nambu-Goldstone particle.

Brans-Dicke accelerated cosmologies with fermionic sources

In the framework of the Brans-Dicke scalar-tensor theory of gravitation, we investigate the role of a self-interacting fermionic field in a universe filled with dust and radiation constituents. This model is shown to present a variety of behaviors, depending on the parameters chosen. In particular, we find that the fermionic field is capable of promoting a transition from an initially decelerated, radiation-dominated period to a later accelerated regime where the fermion prevails. The Brans-Dicke field is found to approach a constant value, and an intermediary matter-dominated era is observed. The dependence of the acceleration on the fermionic potential was also investigated. On a second analysis, the possibility of a direct energy exchange between the constituents was considered, using the dynamical pressure approach. On this later formulation a three-era cosmological regime emerged.

Dark Range of ω In Brans-Dicke Gravity

The variational field equations of Brans-Dicke scalar-tensor theory of gravitation that is coupled to a mass-varying sterile neutrino field are presented in Riemannian and non-Riemannian setting in the language of exterior differential forms over four-dimensional spacetime. In a gravitational plane wave geometry in Rosen coordinates, with the scalar field set equal to a constant, the field equations admit ghost neutrino solutions. These correspond to Majorana spinor configurations for which the total neutrino stress-energy-momentum tensor vanishes. We show here that in the absence of a sterile neutrino in the gravitational wave geometry, there are scalar field configurations for which the total scalar field stress-energy-momentum tensor vanishes for negative values of the Brans-Dicke parameter —3/2 < ω < 0.

Reconsidering holographic dark energy in Brans\u2013Dicke theory

In this paper, we reconsider the concept of holographic dark energy in the framework of Brans–Dicke theory in the formalism of the flat Friedmann–Lemaitre–Robertson–Walker metric. Firstly, we demonstrate how the assumption phi propto a^n, where phi and a stand for the Brans–Dicke scalar field and scale factor, respectively, naturally leads to a constant deceleration parameter, irrespective of the energy content of the universe. Secondly, we consider interacting holographic dark energy with Hubble horizon as IR cut-off, and find the value of the Hubble parameter and corresponding value of the scale factor. Further, we find the value of the Brans–Dicke scalar field phi for the obtained value of the Hubble parameter and holographic dark energy. We obtain the corresponding value of the deceleration parameter and show that it can explain the phase transition of the universe. Moreover, statefinder diagnostics has been applied to compare the model with existing models. On the other hand, we consider the viscous behavior of holographic dark energy and show that the viscous holographic dark energy can play the role of interacting holographic dark energy as it is able to explain the phase transition of the universe. Further, we find the value of the Brans–Dicke scalar field phi for this viscous holographic dark energy. In this model also, we apply the statefinder diagnostic.

Towards Unification of General Relativity and Quantum Theory: Dendrogram Representation of the Event-Universe.

Following Smolin, we proceed to unification of general relativity and quantum theory by operating solely with events, i.e., without appealing to physical systems and space-time. The universe is modelled as a dendrogram (finite tree) expressing the hierarchic relations between events. This is the observational (epistemic) model; the ontic model is based on p-adic numbers (infinite trees). Hence, we use novel mathematics: not only space-time but even real numbers are not in use. Here, the p-adic space (which is zero-dimensional) serves as the base for the holographic image of the universe. In this way our theory is connected with p-adic physics; in particular, p-adic string theory and complex disordered systems (p-adic representation of the Parisi matrix for spin glasses). Our Dendrogramic-Holographic (DH) theory matches perfectly with the Mach’s principle and Brans–Dicke theory. We found a surprising informational interrelation between the fundamental constants, h, c, G, and their DH analogues, h(D), c(D), G(D). DH theory is part of Wheeler’s project on the information restructuring of physics. It is also a step towards the Unified Field theory. The universal potential V is nonlocal, but this is relational DH nonlocality. V can be coupled to the Bohm quantum potential by moving to the real representation. This coupling enhances the role of the Bohm potential.

Violation of the equivalence principle in curvature-based extended gravity at finite temperature

We review the possible violation of the Equivalence Principle at finite temperature [Formula: see text] in the framework of curvature-based Extended Theories of Gravity. Specifically, we first show how it is possible to derive Equivalence Principle violation from Quantum Field Theory at [Formula: see text]. Subsequently, we exhibit how this result can be precisely recovered by following an alternative path that envisages the employment of generalized Einstein equations with a temperature-dependent energy-momentum tensor. Finally, we adopt the latter formalism in the context of some Extended Gravity models to quantify the amount of Equivalence Principle violation. Specifically, Brans–Dicke Theory, Standard Model Extension and Conformal Gravity are considered in detail.

Big Rip Scenario in Brans-Dicke Theory

In this work, we present a Big Rip scenario within the framework of the generalized Brans-Dicke (GBD) theory. In the GBD theory, we consider an evolving BD parameter along with a self-interacting potential. An anisotropic background is considered to have a more general view of the cosmic expansion. The GBD theory with a cosmological constant is presented as an effective cosmic fluid within general relativity which favours a phantom field dominated phase. The model parameters are constrained so that the model provides reasonable estimates of the Hubble parameter and other recent observational aspects at the present epoch. The dynamical aspects of the BD parameter and the BD scalar field have been analysed. It is found that the present model witnesses a finite time doomsday at a time of tBR≃16.14Gyr, and for this scenario, the model requires a large negative value of the Brans-Dicke parameter.