arXiv subjects

A. M. Velásquez-Toribio

Publications and source records attributed to A. M. Velásquez-Toribio.

3 recordsLinked to original sources

arXiv2026

Dynamical systems analysis of unimodular cosmology in $D=4+d$ dimensions

We investigate the effective four-dimensional cosmology induced by unimodular gravity in $D=4+d$ dimensions, where the internal extra-dimensional volume is encoded in a scalar degree of freedom. After dimensional reduction, we show that the resulting FLRW equations admit a natural autonomous formulation whose phase-space structure differs qualitatively from that of general relativity. In the vacuum sector, the reduced system exhibits a continuous family of finite equilibrium points, $λ=dH$, together with well-defined asymptotic Poincaré directions. In the matter sector, we focus on the five-dimensional case $d=1$ and use the reduced Bianchi relation as the consistency condition that links the ordinary matter component to the internal-volume degree of freedom. The system is then closed by adopting the minimal higher-dimensional conservation prescription, according to which matter is diluted by both the external volume and the internal-volume modulus. This leads to a reduced matter--geometry dynamics with isolated critical points and a globally organized compactified flow. Numerical examples illustrate how the internal-volume degree of freedom affects the background evolution and the global phase-space structure. The comparison with $Λ$CDM is used only as a benchmark, while a full observational analysis and more general matter--geometry exchange prescriptions are left for future work.

physics.gen-ph↗

arXiv2026

A dynamical systems approach to studying the equivalence principle in dilaton gravity

We study a string-inspired dilaton cosmology in the Damour--Polyakov (DP) regime using dynamical-systems methods, aiming to make explicit how cosmological relaxation controls deviations from the equivalence principle. Working in the Einstein frame, we consider a spatially flat FLRW universe filled with pressureless matter and a universally coupled dilaton. Expanding the conformal coupling function and the scalar potential around the least-coupling point, we obtain a closed and self-consistent autonomous system governing the late-time evolution of the scalar-matter sector. The resulting phase space contains a stable fixed point associated with least coupling, approached only asymptotically along cosmological trajectories. Therefore, at any finite epoch the solution typically retains a small displacement from the fixed point. In the DP regime this finite-epoch displacement sets the ambient coupling, and thus determines the magnitude of fifth-force effects and deviations from the equivalence principle in the nonrelativistic limit. By linearising the system around a finite-epoch reference state, we show that the damping of the displacement is controlled by the Jacobian eigenvalues of the DP fixed point. This yields a direct dynamical estimate of how rapidly deviations from the equivalence principle are reduced during cosmological evolution. The mechanism is global and cosmological in origin, and is conceptually distinct from local environmental screening as in chameleon or symmetron scenarios. Overall, our results illustrate how phase-space techniques provide a clear bridge between cosmological dynamics and weak-field departures from General Relativity.

astro-ph.CO↗

arXiv2020

The growth factor parametrization versus numerical solutions in flat and non-flat dark energy models

In the present investigation we use observational data of $ f σ_ {8} $ to determine observational constraints in the plane $(Ω_{m0},σ_{8})$ using two different methods: the growth factor parametrization and the numerical solutions method for density contrast, $δ_{m}$. We verified the correspondence between both methods for three models of accelerated expansion: the $ΛCDM$ model, the $ w_{0}w_{a} CDM$ model and the running cosmological constant $RCC$ model. In all case we consider also curvature as free parameter. The study of this correspondence is important because the growth factor parametrization method is frequently used to discriminate between competitive models. Our results we allow us to determine that there is a good correspondence between the observational constrains using both methods. We also test the power of the $ fσ_ {8} $ data to constraints the curvature parameter within the $ ΛCDM $ model. For this we use a non-parametric reconstruction using Gaussian processes. Our results show that the $ fσ_ {8}$ data with the current precision level does not allow to distinguish between a flat and non-flat universe.

astro-ph.CO↗