arXiv subjects

A. M

Publications and source records attributed to A. M.

3 recordsLinked to original sources

arXiv2026

A Stochastic Framework for the Spherical Jeans Equation Motivated by Scalar-Tensor Gravity

We develop a stochastic framework for the stationary spherical Jeans equation, motivated by the field-dependent nature of the gravitational coupling in scalar--tensor theories. We model unresolved spatial fluctuations of the scalar sector as an effective stochastic contribution to the gravitational coupling, $\Geff(r,\omega)=\Gbar(r)+\Gamma_G(r)\xi(r,\omega)$. This approach induces a linear It\^o stochastic differential equation for the radial velocity dispersion $y(r)=\sigma_r^2(r)$, defining a nonautonomous radial random flow rather than a time-evolution problem. We derive the associated Fokker--Planck equation and obtain integral expressions for the mean, variance, and covariance of the radial velocity dispersion. Because the noise is additive, the deterministic Jeans solution is recovered as the mean profile, while the stochastic sector produces a probability band around it. We specialize the construction to Navarro--Frenk--White, Hernquist, and Einasto halo models and propagate the radial covariance to the projected line-of-sight velocity dispersion. This provides a semi-analytical framework for assessing how effective gravitational fluctuations can affect halo kinematic observables in the stationary Jeans regime.

astro-ph.CO↗

arXiv2026

The Scalar Mach-Sciama Theory of Gravitation

We formulate a scalar realization of Sciama's Machian programme within the general Bergmann-Wagoner class of scalar--tensor gravity. Starting from a universally conformally coupled matter sector, we rewrite the field equations in terms of the invariant set $\{{\cal I}_1,{\cal I}_2,{\cal I}_3,\hat g_{\mu\nu}\}$, so that Machian requirements can be stated independently of conformal frame. Sciama's causal postulate is implemented not by modifying the local dynamics, but as a selection rule on the solution space of the invariant scalar equation: the admissible configuration is the retarded response to the matter distribution in the causal past, with any source-free contribution removed. In a spatially flat FLRW universe, and in the light, slowly varying regime, the prescription reduces to an explicit temporal kernel that links the background scalar evolution to the matter content within the Hubble region, reproducing the expected Machian scaling in an expanding background. Universal coupling to a single physical metric implies that structureless test bodies share the same acceleration in a given external configuration, so that the E\"otvs parameter vanishes at leading order. Nonuniversal effects can arise only when gravitational binding energy contributes appreciably to the total mass, as in strongly self-gravitating objects. Thus, the theory implements a causal Machian determination of the cosmological inertial scale while remaining consistent with standard weak-field tests.

gr-qc↗

arXiv2020

Observational constraints on the non-flat $\Lambda CDM$ model and a null test using the transition redshift

A natural extension of the standard cosmological model are models that include curvature as a free parameter. In this work we study in detail the observational constraints on the non-flat $\Lambda CDM$ model using the two main geometric tests: SNIa and Hubble parameter measurements. In general we show that the observational constraints on the parameters of the $\Lambda CDM$ model strongly depend on the curvature parameter. In particular, we study the constraints on the transition redshift ($z_{t}$) of a universe dominated by matter for a universe dominated by the cosmological constant. Using this observable we construct a new null test defining $\zeta = z_{t, flat}-z_{t, non flat}$. This test depends only on the data of the Hubble parameter, the Hubble constant and the matter density parameter. However, it does not depend on derivative of an observable as generally many tests in the literature. To reconstruct this test, we use the Gaussian process method. When we use the best-fit parameters values of $PLANCK/2018$, we find no evidence of a disagreement between the data and the standard model (flat $\Lambda CDM$), but if we use the value $H_{0}$ from $RIESS/2018$ we found a disagreement with respect at the standard model. However, it is important to note that the Hubble parameter data has large errors for a solid statistical analysis.

astro-ph.CO↗