arXiv subjects

John W. Moffat

Publications and source records attributed to John W. Moffat.

At least 19 recordsLinked to original sources

arXiv2026

Stueckelberg Gauge Invariant Formulation of MOG

We develop a Stueckelberg gauge-invariant formulation of modified gravity (MOG). The massive vector field is made gauge-invariant by introducing a compensating scalar field, without requiring a Higgs field, spontaneous symmetry breaking, or a vacuum expectation value to fix the effective Newtonian gravitational coupling. This separates the gauge-invariant origin of the vector mass from the cosmological evolution of the gravitational coupling. The formulation preserves the finite-range vector interaction of MOG, while allowing the effective gravitational coupling to be treated as an independent scalar or scale-dependent quantity. This distinction is important for cosmological tests, since early-universe constraints and late-time large-scale gravitational phenomena need not be tied to a symmetry-breaking vacuum. The Stueckelberg formulation provides a gauge-invariant framework for comparing MOG with nucleosynthesis, cosmic microwave background, large-scale structure, lensing, and distance data.

gr-qc↗

arXiv2026

CMB Acoustic Power Spectra in STVG-MOG

We present a cosmological realization of Scalar--Tensor--Vector Gravity (STVG--MOG) in which the pre-recombination scalar perturbation dynamics become degenerate with those of $Λ$CDM without invoking particle dark matter. In the early universe, nonrelativistic excitations of the massive STVG vector field $ϕ_μ$ behave as a collisionless, pressureless component with vanishing sound speed and background density $ρ_ϕ\propto a^{-3}$. On the Fourier scales relevant for the acoustic peaks, the effective gravitational coupling satisfies $G_{\rm eff}(k,a)\simeq G_N$, so that the metric potentials governing baryon--photon oscillations evolve in the same way as in the standard cosmological model. The gravitational wells remain sufficiently deep at horizon entry to preserve the observed height of the third acoustic peak, the most sensitive indicator of a clustering pressureless component prior to recombination. Since Thomson scattering, recombination, baryon loading, and photon diffusion are unchanged, the temperature and polarization spectra can coincide with the standard $Λ$CDM predictions once the vector sector supplies the effective dust component. In this framework, the dynamical role usually attributed to cold dark matter is carried instead by a degree of freedom belonging to the gravitational sector itself. We explain why this vector-sector dust, although dynamically degenerate with cold dark matter in the early universe, is not equivalent to a particle dark matter fluid. The Boltzmann code CLASS is used to obtain a MOG fit to the acoustical power spectrum data.

astro-ph.CO↗

arXiv2026

STVG-MOG Cluster Dynamics and the Cosmological $1/r^2$ Force Law from Pairwise kSZ Data

We investigate whether Scalar-Tensor-Vector Gravity in its weak-field modified gravity form can account for the cluster-scale inverse-square force law inferred from recent kinematic Sunyaev-Zeldovich measurements of cluster pairwise motions. The starting point is the X-COP cluster fit of STVG-MOG, for which a representative baryonic cluster mass $M\sim 10^{15}M_\odot$ together with parameters $α\sim 9.11$ and $μ\sim 0.196~{\rm Mpc}^{-1}$ provides a successful description of cluster dynamics without particle dark matter. We extrapolate this fit to the separation range $30$ to $230~{\rm Mpc}$, relevant for the pairwise kSZ analysis. Since the Yukawa transition length $μ^{-1}\simeq 5.1~{\rm Mpc}$ is much smaller than these separations, the STVG-MOG acceleration law reduces to an effective inverse-square form. This explains why the theory can satisfy the observed Newtonian behavior while remaining distinct from MOND-like long-distance modifications. We derive the corresponding pairwise velocity curve and show that, after fitting a single overall kSZ amplitude, the extrapolated STVG-MOG prediction reproduces the measured trend of the pairwise kSZ data. The analysis shows that the X-COP cluster fit and the cosmological-scale kSZ force-law result are mutually consistent within STVG-MOG.

astro-ph.CO↗

arXiv2026

Isotropic Equivalence of STVG--MOG and $Λ$CDM and Its Breakdown in Large--Scale Anisotropic Cosmological Observables

We show that Scalar-Tensor-Vector Gravity (STVG-MOG) is observationally equivalent to the standard model $Λ$CDM cosmological model for all probes that depend on isotropic and linear gravitational dynamics, including galaxy rotation curves, cluster lensing, the linear matter power spectrum P(k), $σ_8$, baryon acoustic oscillations, and the cosmic microwave background (CMB). This degeneracy arises from the scale-dependent effective gravitational coupling $G_{\mathrm{eff}}$, which ensures identical background evolution, transfer functions, and linear growth. Consequently, all early-universe, low and intermediate scale cosmological observables are equally well described by STVG-MOG without invoking non-baryonic dark matter. We argue that the equivalence implies that isotropic cosmological data alone cannot establish the physical existence of dark matter. The degeneracy is broken only by observables sensitive to large-scale, anisotropic gravitational response. In particular, recent measurements of enhanced radio-galaxy and quasar number-count dipoles at gigaparsec scales probe a regime where $G_{\mathrm{eff}}$ departs from its $Λ$CDM limit, allowing STVG-MOG to generate anisotropic bulk flows, while preserving consistency with all isotropic constraints. These observations provide a concrete pathway for empirically distinguishing modified gravity from particle dark matter.

astro-ph.CO↗

arXiv2025

Regular Rotating Black Hole: Probing the boundaries of the Radiative Signatures and Jet Power

We perform a detailed observational analysis of several galactic X-ray binaries, focusing on the interplay between black hole spin, jet power, and radiative efficiency within the context of Blandford-Znajek-powered jets. Using updated measurements from continuum fitting and Fe-line methods, we constrain the spin parameter a and the deviation parameter $β$ for five key black hole systems: H1743-322, XTE J1550-564, GRS 1124-683, GRO J1655-40, and GRS 1915+105. For each system, we compare the allowed parameter spaces derived independently from observed radiative efficiencies and emitted jet powers under different assumptions for the jet Lorentz factor $Γ=2,5$. By overlapping these observational constraints with theoretical expectations for regular black holes, we assess the viability of various spin-deviation combinations in explaining the observed phenomena. Our results reveal significant restrictions on the allowed values of $β$, with typical upper bounds around 0.38 - 0.4, except for rapidly spinning sources where the constraint becomes notably tighter. We further present a modified method for generating rotating solutions from static regular black hole spacetimes and provide a robust theoretical framework for relating jet power to black hole angular frequency in curved geometries. We also find that the theoretical jet power is modified by regularization factor for regular black holes. These findings place stringent observational bounds on deviations from the Kerr geometry and provide important insight into the astrophysical mechanisms powering accreting stellar-mass black holes.

astro-ph.HE↗

arXiv2025

Void and Density Walls Inhomogeneous Cosmic Web And Dark Energy

Recent observations from the Dark Energy Spectroscopic Instrument (DESI 2025) indicate a weakening of cosmic acceleration at low redshifts $z < 1$, with effective dark energy equation of state parameters $w_0 > -1$ and $w_a < 0$. We demonstrate that this evolution in dark energy can be explained by cosmic inhomogeneities and the Cosmic Web without modifying fundamental physics. Our model shows how the differential expansion between underdense voids and overdense walls creates an effective backreaction term that simulates evolving dark energy when interpreted within homogeneous cosmological frameworks. The inhomogeneous cosmic structure formation becomes significant $z\sim 1-2$, the increasing gravitational influence of wall regions counteracting the cosmic acceleration, producing both a weakening acceleration signal and a direction-dependent Hubble parameter consistent with local measurements. This mechanism reconciles the higher locally measured Hubble constant $H_0\approx 73~ km/s/Mpc$ with the lower value inferred from CMB observations $H_0\approx 67-69~ km/s/Mpc$ without introducing new energy components or modifying general relativity. Our model makes testable predictions regarding directional and scale-dependent variations in cosmological parameters that can be verified with next-generation surveys. This work suggests that properly accounting for cosmic structure may be essential for resolving apparent tensions in cosmological parameters.

astro-ph.CO↗

arXiv2025

Zero Mass limit of Kerr-MOG Black Hole Equals Wormhole

It has been argued in existing literature that the zero mass limit of Kerr spacetime corresponds to either flat Minkowski spacetime or a wormhole exhibiting a locally flat geometry. In this study, we examine that the zero mass limit of the Kerr-MOG black hole is equivalent to a wormhole. Moreover, we derive the Kerr-Schild form of the Kerr-MOG black hole through specific coordinate transformations. We further investigate the physical and topological characteristics of the Kerr-MOG black hole within the framework of modified gravity. Our analysis also includes a discussion of the wormhole using cylindrical coordinates, which comprises two distinct coordinate patches. Furthermore, we extend our analysis to the Kerr-Newman black hole and show that the \emph{zero mass limit of the Kerr-Newman black hole does not yield a wormhole}. However, if we impose an additional criterion such that \emph{both the mass parameter and the charge parameters are equal to zero}, then the Kerr-Newman black hole will be a wormhole.

gr-qc↗

arXiv2025

Complex Riemannian spacetime and singularity-free black holes and cosmology

An approach is presented to address singularities in general relativity using a complex Riemannian spacetime extension. We demonstrate how this method can be applied to both black hole and cosmological singularities, specifically focusing on the Schwarzschild and Kerr black holes and the Friedmann-Lemaître-Robertson-Walker (FLRW) Big Bang cosmology. By extending the relevant coordinates into the complex plane and carefully choosing integration contours, we show that it is possible to regularize these singularities, resulting in physically meaningful, singularity-free solutions when projected back onto real spacetime. The removal of the singularity at the Big Bang allows for a bounce cosmology. This approach offers a potential bridge between classical general relativity and quantum gravity effects, suggesting a way to resolve longstanding issues in gravitational physics without requiring a full theory of quantum gravity.

gr-qc↗

arXiv2025

Stochastic Fluctuations and Brownian Motion Detection of Gravitons

We propose a way to detect gravitons by replicating the Brownian motion experiment. The number $N_g$ of gravitons can be large enough for the stochastic gravitational noise produced by them to displace a massive test particle in a physical system, allowing for the detection of gravitons. Possible experiments to detect gravitons are proposed involving collective stochastic fluctuations due to a large number of gravitons, causing a Brownian motion displacement of a massive test body. Gravitational wave experiments involving advanced interferometer techniques and mirrors could detect the large collective number of gravitons, and could detect Brownian motion of test particles in the detectors' component mirrors. The problem of reducing thermal and other background noise is investigated.

gr-qc↗

arXiv2025

Gravitational Wave and Quantum Graviton Interferometer Arm Detection of Gravitons

This paper explores the quantum and classical descriptions of gravitational wave detection in interferometers like LIGO. We demonstrate that a graviton scattering and quantum optics model succeeds in explaining the observed arm displacements, while the classical gravitational wave approach and a quantum graviton energy method also successfully predict the correct results. We provide a detailed analysis of why the quantum graviton energy approach succeeds, highlighting the importance of collective behavior and the quantum-classical correspondence in gravitational wave physics. Our findings contribute to the ongoing discussion about the quantum nature of gravity and its observable effects in macroscopic physics.

gr-qc↗

arXiv2024

Shadow of regular black hole in scalar-tensor-vector gravity theory

We investigate the shadow cast by a regular black hole in scalar-tensor-vector mOdified gravity theory. This black hole differs from a Schwarzschild-Kerr black hole by the dimensionless parameter $β$. The size of the shadow depends on this parameter. Increasing the value of the parameter $β$ shrinks the shadow. A critical value of the parameter $β$ is found to be $β_{\rm crit}=0.40263$. The shadow for the horizonless dark compact object has been analysed for the static, spherically symmetric case and compared with M87* and Sgr A* data. Shadow observables have been determined in the context of the regular black hole and used for obtaining the energy emission rate. The peak of the energy emission rate shifts to lower frequency for the increasing value of the parameter $β$.

gr-qc↗

arXiv2024

Wide Binaries and Modified Gravity (MOG)

Wide binary stars are used to test the modified gravity called Scalar-Tensor-Vector Gravity or MOG. This theory is based on the additional gravitational degrees of freedom, the scalar field $G=G_N(1+α)$, where $G_N$ is Newton's constant, and the massive (spin-1 graviton) vector field $ϕ_μ$. The wide binaries have separations of 2-30 kAU. The MOG acceleration law, derived from the MOG field equations and equations of motion of a massive test particle for weak gravitational fields, depends on the enhanced gravitational constant $G=G_N(1+α)$ and the effective running mass $μ$. The magnitude of $α$ depends on the physical length scale or averaging scale $\ell$ of the system. The modified MOG acceleration law for weak gravitational fields predicts that for the solar system and for the wide binary star systems gravitational dynamics follows Newton's law.

gr-qc↗

arXiv2024

Scalar-tensor-vector-gravity and NGC-1277

NGC1277 is a compact but massive lenticular galaxy that shows no signs of the presence of dark matter. We find that this galaxy's behavior is consistent not only with Newtonian dynamics, but also with the predictions of Scalar--Tensor--Vector--Gravity, also known as MOG (MOdified Gravity). The compact size of the galaxy, in combination with its large mass, ensures that there are no observable deviations between the predictions of Newtonian and MOG orbital velocities within the galaxy's visible radius.

astro-ph.GA↗

arXiv2021

External Field Effect in Gravity

In both Newtonian gravity and Einstein gravity there is no force on a test particle located inside a spherical cavity cut out of a static, spherically symmetric mass distribution. Inside the cavity exterior matter is decoupled and there is no external field effect that could act on the test particle. However, for potentials other than the Newtonian potential or for geometries other than Ricci flat ones this is no longer the case, and there then is an external field effect. We explore this possibility in various alternate gravity scenarios, and suggest that such (Machian) external field effects can serve as a diagnostic for gravitational theory.

gr-qc↗

arXiv2018

Superradiance in Modified Gravity (MOG)

We consider the case of rotating black holes in a dark-matter-emulating theory of gravity called MOG. The latter introduces a gravitational vector field with an associated gravitational charge proportional to the black hole mass and a scalar field in place of the gravitational constant. The resulting black hole metrics resemble the Kerr-Newman geometry and enjoy superradiant scattering. MOG, however, presents important new features. By studying the scattering of a scalar field, we show that there is a marked reduction of the critical frequency of mode amplification. This corresponds to saying that the superradiance peak frequency is red shifted. Analyses of the reflected energy flux also show that MOG black holes are fainter with respect to the standard ones. The proposed results pave the way for testing MOG against astronomical observations.

gr-qc↗

arXiv2017

Local conformal symmetry in non-Riemannian geometry and the origin of physical scales

We introduce an extension of the Standard Model and General Relativity built upon the principle of local conformal invariance, which represents a generalization of a previous work by Bars, Steinhardt and Turok. This is naturally realized by adopting as a geometric framework a particular class of non-Riemannian geometries, first studied by Weyl. The gravitational sector is enriched by a scalar and a vector field. The latter has a geometric origin and represents the novel feature of our approach. We argue that physical scales could emerge from a theory with no dimensionful parameters, as a result of the spontaneous breakdown of conformal and electroweak symmetries. We study the dynamics of matter fields in this modified gravity theory and show that test particles follow geodesics of the Levi-Civita connection, thus resolving an old criticism raised by Einstein against Weyl's original proposal.

hep-th↗

arXiv2016

Black Hole Thermodynamics in MOdified Gravity (MOG)

We analyze the thermodynamical properties of black holes in a modified theory of gravity, which was initially proposed to obtain correct dynamics of galaxies and galaxy clusters without dark matter. The thermodynamics of non-rotating and rotating black hole solutions resembles similar solutions in Einstein-Maxwell theory with the electric charge being replaced by a new mass dependent gravitational charge $Q = \sqrt{αG_N}M$. This new mass dependent charge modifies the effective Newtonian constant from $G_N$ to $G = G_N(1+α)$, and this in turn critically affects the thermodynamics of the black holes. We also investigate the thermodynamics of regular solutions, and explore the limiting case when no horizons forms. So, it is possible that the modified gravity can lead to the absence of black hole horizons in our universe. Finally, we analyze corrections to the thermodynamics of a non-rotating black hole and obtain the usual logarithmic correction term.

gr-qc↗

arXiv2012

Modified Jordan-Brans-Dicke theory with scalar current and the Eddington-Robertson gamma-parameter

The Jordan-Brans-Dicke theory of gravitation, which promotes the gravitational constant to a dynamical scalar field, predicts a value for the Eddington-Robertson post-Newtonian parameter gamma that is significantly different from the general relativistic value of unity. This contradicts precision solar system measurements that tightly constrain gamma around 1. We consider a modification of the theory, in which the scalar field is sourced explicitly by matter. We find that this leads to a modified expression for the gamma-parameter. In particular, a specific choice of the scalar current yields gamma=1, just as in general relativity, while the weak equivalence principle is also satisfied. This result has important implications for theories that mimic Jordan-Brans-Dicke theory in the post-Newtonian limit in the solar system, including our scalar-tensor-vector modified gravity theory (MOG).

gr-qc↗