arXiv subjects

Z. C. Santana

Publications and source records attributed to Z. C. Santana.

4 recordsLinked to original sources

arXiv2026

Tracing the Evolution of $Ω_m(z)$ over the Last 10 Billion Years with Non-parametric Methods

We investigate the redshift evolution of the matter density parameter, $Ω_m(z)$, using galaxy cluster gas mass fraction measurements combined with cosmic chronometer $H(z)$ data and type Ia supernova luminosity distances. This provides a non-parametric probe of the normalization of the cosmological matter sector, which plays a central role in current tensions involving weak lensing measurements, cluster abundance analyses, and the $S_8$ parameter. Using Gaussian Process regression, we reconstruct $Ω_m(z)$ without assuming a parametric form for its evolution. The reconstructed evolution is consistent with the standard $ρ_m \propto (1+z)^3$ scaling predicted by the $Λ$CDM model. We obtain $Ω_{m0}=0.296 \pm 0.044$ from the 44-cluster sample, and $Ω_{m0}=0.271 \pm 0.016$, $0.253 \pm 0.017$, and $0.210 \pm 0.013$ for the 103-cluster compilation, depending on the adopted mass calibration. While the reconstructed $Ω_m(z)$ evolution remains consistent with the expected $Λ$CDM behaviour, the inferred normalization of $Ω_{m0}$ depends strongly on the adopted cluster mass calibration. Consequently, cluster mass calibration systematics constitute the dominant source of uncertainty in the inferred normalization of $Ω_{m0}$, exceeding the statistical uncertainties of the non-parametric reconstruction.

astro-ph.CO↗

arXiv2025

A Joint Analysis of Strong Lensing and Type Ia Supernovae to Determine the Hubble Constant

We present a cosmological model-independent determination of the Hubble constant, $H_0$, by combining time-delay measurements from seven TDCOSMO systems, Einstein radius measurements, and Type Ia Supernovae data sourced from the Pantheon+ sample. For each lens of time-delay system, we calculate the angular diameter distance $D_{A_l}$ using the product $D^{\textrm{Obs}}(z_l) \cdot D_{A,Δt}^{\textrm{Obs}}(z_l, z_s)$, where $D^{\textrm{Obs}}(z_l)$ is reconstructed via Gaussian Processes from 99 Einstein radius measurements, and $D_{A,Δt}^{\textrm{Obs}}(z_l,z_s)$ is the time-delay angular distance. We also reconstruct the unanchored luminosity distance $H_0 D_L(z_l)$ from supernova data. By using the cosmic distance duality relation validity, we anchor $D_{A_l}$ and $H_0 D_L(z_l)$ to infer $H_0 = 70.55 \pm 7.44$ km/s/Mpc (68\% CL). Our result, though not resolving the Hubble tension, offers a cosmological model-independent consistency check and highlights the potential of using strong lensing and supernovae data via the cosmic distance duality relation to constrain $H_0$.

astro-ph.CO↗

arXiv2024

Non-Parametric Analysis for the Dark Matter Density Evolution

In this paper, we investigate a potential departure in the standard dark matter density evolution law, $ρ_{dm} = ρ_{dm,0}(1+z)^3$. The method involves considering a deformed evolution model, denoted as $ρ_{dm} = ρ_{dm,0}(1+z)^3f(z)$, and searching the presence of any deviation ($f(z)\neq 1$). As one may see, $f(z)$ is a general function that parametrizes a possible digression from the standard law. We use data of baryon acoustic oscillations, type I Supernovae luminosity distances, and galaxy cluster gas mass fraction observations to reconstruct $f(z)$ through an approach that is not dependent on the cosmological model or the so-called Gaussian process regression. Unlike previous works, it enables us to investigate a possible deviation without using a specific function to describe it. We have obtained $f(z)=1$, the standard model scenario, within $2σ$ c.l. in all the considered cases.

astro-ph.CO↗

arXiv2024

Interaction in the dark sector: a phenomenological approach

The non-gravitational interaction between the dark components of the Universe could lead to the variation of dark matter energy density standard evolution law. When we assume this scenario, the dark matter energy density follows $ρ_{dm}\sim(1+z)^{3 + ε(z)}$ (where $ε(z)=0$ the standard law is recovered). In this paper, we perform a Bayesian analysis to test three parameterizations for $ε(z)$, namely: $ε(z)=ε_0$, $ε(z)=ε_0 + ε_1\frac{z}{1+z}$ and $ε(z)=ε_0 + ε_1\frac{z(1+z)}{1+z^2}$, where the first one is motivated through the fundamental grounds and the others are on the phenomenological ones. Through the Gaussian process regression, our method uses galaxy cluster gas mass fraction measurements, SNe Ia observations, Cosmic Chronometers, and BAO data. No specific cosmological model is considered. In all possibilities analyzed, the standard evolution law ($ε(z)=0$) is within $2σ$ c.l. The investigated cases generally indicated scenarios of inconclusive or weak evidence toward the simplest model from the Bayesian standpoint.

astro-ph.CO↗