arXiv subjects

L. R. Colaço

Publications and source records attributed to L. R. Colaço.

13 recordsLinked to original sources

arXiv2026

Investigating a Possible Variation of the Gravitational Constant Through Gas Mass Fraction Measurements and Type Ia Supernovae Observations

In this paper, we investigate a possible time variation of the gravitational constant (G) using a non-parametric approach. Our main cosmological probe is the gas mass fraction of galaxy clusters measured from X-ray observations. We also account for the effect of a varying $G$ on the intrinsic luminosity of type Ia supernovae (SNe Ia) through the Chandrasekhar mass-luminosity relation. We consider a specific phenomenological scenario, motivated by some scalar-tensor and screened modified-gravity frameworks, in which the standardized luminosity of SNe Ia decreases with increasing Chandrasekhar mass. Using gas mass fraction measurements jointly with luminosity distances from the Pantheon+ compilation, we reconstruct the evolution of G through Gaussian Processes. Our results indicate that a constant gravitational coupling remains broadly consistent with the data, although mild low-redshift departures are allowed.

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↗

arXiv2025

A Hubble Constant Determination Through Quasar Time Delays and Type Ia Supernovae

This paper presents a new model-independent constraint on the Hubble constant ($H_0$) by anchoring relative distances from Type Ia supernovae (SNe Ia) observations to absolute distance measurements from time-delay strong Gravitational Lensing (SGL) systems. The approach only uses the validity of the cosmic distance duality relation (CDDR) to derive constraints on $H_0$. By using Gaussian Process (GP) regression to reconstruct the unanchored luminosity distance from the Pantheon$+$ compilation to match the time-delay angular diameter distance at the redshift of the lenses, one yields a value of $H_0 = 75.57 \pm 4.415$ km/s/Mpc at a 68\% confidence level. The result aligns well with the local estimate from Cepheid variables within the $1σ$ confidence region, indicating consistency with late-universe probes.

astro-ph.CO↗

arXiv2024

Non-parametric reconstruction of the fine structure constant with galaxy clusters

Testing possible variations in fundamental constants of nature is a crucial endeavor in observational cosmology. This paper investigates potential cosmological variations in the fine structure constant ($α$) through a non-parametric approach, using galaxy cluster observations as the primary cosmological probe. We employ two methodologies based on galaxy cluster gas mass fraction measurements derived from X-ray and Sunyaev-Zeldovich observations, along with luminosity distances from type Ia supernovae. We also explore how different values of the Hubble constant ($H_0$) impact the variation of $α$ across cosmic history. When using the Planck satellite's $H_0$ observations, a constant $α$ is ruled out at approximately the 3$σ$ confidence level for $z \lesssim 0.5$. Conversely, employing local estimates of $H_0$ restores agreement with a constant $α$.

astro-ph.CO↗

arXiv2024

A Hubble Constant Estimate from Galaxy Cluster and type Ia SNe Observations

In this work, we constrain the Hubble constant parameter, $H_0$, using a combination of the Pantheon sample and galaxy clusters (GC) measurements from minimal cosmological assumptions. Assuming the validity of the cosmic distance duality relation, an estimator is created for $H_0$ that only depends on simple geometrical distances, which is evaluated from Pantheon and a GC angular diameter distance sample afterward. The statistical and systematic errors in GC measurements are summed in quadrature in our analysis. We find $H_0 = 67.22 \pm 6.07$ ${\rm km \ s^{-1} Mpc^{-1}}$ in $1σ$ confidence level (C.L.). This measurement presents an error of around 9\%, showing that future and better GC measurements can shed light on the current Hubble tension

astro-ph.CO↗

arXiv2023

Forecasts analysis on varying-$α$ theories from gravitational wave standard sirens

Motivated by future gravitational waves observations, we perform forecasts analysis to constrain a possible time variation of the fine structure constant ($α$) within the context of the so-called runaway dilaton model. For this purpose, some gravitational-wave standard sirens mock data within the perspective of Einstein Telescope and LISA mission were considered jointly with current strong gravitational lensing systems observations. We find that future standard sirens observations can also play an important role in the search for possible variations of $α$ within the methodology presented in this work.

astro-ph.CO↗

arXiv2022

Constraining a possible time-variation of the speed of light along with the fine-structure constant using strong gravitational lensing and Type Ia supernovae observations

The possible time variation of the fundamental constants of nature has been an active subject of research since the large-number hypothesis was proposed by Dirac. In this paper, we propose a new method to investigate a possible time variation of the speed of light ($c$) along with the fine-structure constant ($α$) using Strong Gravitational Lensing (SGL) and Type Ia Supernovae (SNe Ia) observations. We assume a general approach to describe the mass distribution of lens-type galaxies, the one in favor of the power-law index model (PLAW). We also consider the runaway dilaton model to describe a possible time-variation of $α$. In order to explore the results deeply, we split the SGL sample into five sub-samples according to the lens stellar velocity dispersion and three sub-samples according to lens redshift. The results suggest that it is reasonable to treat the systems separately, but no strong indication of varying $c$ was found.

astro-ph.CO↗

arXiv2021

Gravitational lens time-delay as a probe of a possible time variation of the fine-structure constant

A new method based on large-scale structure observations is proposed to probe a possible time variation of the fine-structure constant ($α$). Our analyses are based on time-delay of Strong Gravitational Lensing and Type Ia Supernovae observations. By considering a class of runaway dilaton models, where the cosmological evolution of the fine-structure constant is given by $\frac{Δα}α \approx -γ\ln{(1+z)}$, we obtain limits on the physical properties parameter of the model ($γ$) at the level $10^{-2}$ ($1σ$). Although our limits are less restrictive than those obtained by quasar spectroscopy, the approach presented here provides new bounds on the possibility of $\frac{Δα}α \neq 0$ at a different range of redshifts.

astro-ph.CO↗

arXiv2021

Probing variation of the fine-structure constant in runaway dilaton models using Strong Gravitational Lensing and Type Ia Supernovae

In order to probe a possible time variation of the fine-structure constant ($α$), we propose a new method based on Strong Gravitational Lensing and Type Ia Supernovae observations. By considering a class of dilaton runaway models, where $\frac{Δα}α= - γ\ln{(1+z)}$, we obtain constraints on $\frac{Δα}α$ at the level $γ\approx 10^{-2}$ ($γ$ captures the physical properties of the model). Since the data set covers the redshift range $0.075 \leq z \leq 2.2649$, the constraints derived here provide independent bounds on a possible time variation of $α$ at low, intermediate and high redshifts.

astro-ph.CO↗

arXiv2019

Galaxy cluster Sunyaev-Zel'dovich effect scaling-relation and type Ia supernova observations as a test for the cosmic distance duality relation

In this paper, we propose a new test to the cosmic distance duality relation (CDDR), $D_L=D_A(1+z)^2$, where $D_L$ and $D_A$ are the luminosity and angular diameter distances, respectively. The data used correspond to 61 Type Ia Supernova luminosity distances and $Y_{SZE}-Y_X$ measurements of 61 galaxy clusters obtained by the {\it Planck} mission and the deep XMM-Newton X-ray data, where $Y_{SZE}$ is the integrated comptonization parameter obtained via Sunyaev-Zel'dovich effect observations and $Y_X$ is the X-ray counterpart. More precisely, we use the $Y_{SZE}D_{A}^{2}/C_{XSZE}Y_X$ scaling-relation and a deformed CDDR, such as $D_L/D_A(1+z)^2=η(z)$, to verify if $η(z)$ is compatible with the unity. Two $η(z)$ functions are used, namely, $η(z)=1+η_0 z$ and $η(z)=1+η_0 z /(1+z)$. { We obtain that the CDDR validity ($η_0=0$) is verified within $\approx 1.5σ$ c.l. for both $η(z)$ functions.}.

astro-ph.CO↗

arXiv2019

Galaxy clusters and a possible variation of the fine structure constant

Galaxy clusters have been used as a cosmic laboratory to verify a possible time variation of fundamental constants. Particularly, it has been shown that the ratio $Y_{SZ}D_{A}^{2}/C_{XZS}Y_X $, which is expected to be constant with redshift, can be used to probe a variation of the fine structure constant, $α$. In this ratio, $Y_{SZ}D_{A}^{2}$ is the integrated comptonization parameter of a galaxy cluster obtained via Sunyaev-Zel'dovich (SZ) effect observations multiplied by its angular diameter distance, $D_A$, $Y_X$ is the X-ray counterpart and $C_{XSZ}$ is an arbitrary constant. Using a combination of SZ and X-ray data, a recent analysis found $Y_{SZ}D_{A}^{2}/C_{XZS}Y_X = {\rm{C}} α(z)^{3.5}$, where ${\rm{C}}$ is a constant. In this paper, following previous results that suggest that a variation of $α$ necessarily leads to a violation of the cosmic distance duality relation, $D_L/D_A(1+z)^2 = 1$, where $D_L$ is the luminosity distance of a given source, we derive a new expression, $Y_{SZ}D_{A}^{2}/C_{XSZ}Y_X = {\rm{C}} α^{3.5} η^{-1}(z)$, where $η(z) = D_L/D_A(1+z)^2$. In particular, considering the direct relation $η(z) \propto α(z)^{1/2}$, derived from a class of dilaton runaway models, %class of modified gravity theories, and 61 measurements of the ratio $Y_{SZ}D_{A}^{2}/C_{XSZ}Y_X$ provided by the Planck collaboration, we discuss bounds on a possible variation of $α$. We also estimate the value of the constant $ {\rm{C}}$, which is compatible with the unity at $2σ$ level, indicating that the assumption of isothermality for the temperature profile of the galaxy clusters used in the analysis holds.

astro-ph.CO↗

arXiv2017

Limits on evolution of the fine-structure constant in runaway dilaton models from Sunyaev-Zeldovich Observations

In this paper, new bounds on possible variations of the fine structure constant, $α$, for a class of runaway dilaton models are performed. By considering a possible evolution with redshift, $z$, such as $\frac{Δα}α=-γ\ln(1+z)$, where in $γ$ are the physical properties of the model, we constrain this parameter by using a deformed cosmic distance duality relation jointly with gas mass fraction (GMF) measurements of galaxy clusters and luminosity distances of type Ia supernovae. The GMF's used in our analyses are from cluster mass data from 82 galaxy clusters in the redshift range $0.12<z<1.36$, detected via the Sunyaev-Zeldovich effect at 148 GHz by the Atacama Cosmology Telescope. The type Ia supernovae are from the Union2.1 compilation. We also explore the dependence of the results from four models used to describe the galaxy clusters. As a result no evidence of variation was obtained.

astro-ph.CO↗

arXiv2016

Galaxy clusters, type Ia supernovae and the fine structure constant

As is well known, measurements of the Sunyaev-Zeldovich effect can be combined with observations of the X-ray surface brightness of galaxy clusters to estimate the angular diameter distance to these structures. In this paper, we show that this technique depends on the fine structure constant, $α$. Therefore, if $α$ is a time-dependent quantity, e.g., $α=α_0 ϕ(z)$, where $ϕ$ is a function of redshift, we argue that current data do not provide the real angular diameter distance, $D_{\rm{A}}(z)$, to the cluster but instead $D_A^{data}(z) = ϕ(z)^2 D_{\rm{A}}(z)$. We use this result to derive constraints on a possible variation of $α$ for a class of dilaton runaway models considering a sample of 25 measurements of $D_A^{data}(z)$ in redshift range $0.023 < z < 0.784$ and estimates of $D_{\rm{A}}(z)$ from current type Ia supernovae observations. We find no significant indication of variation of $α$ with the present data.

astro-ph.CO↗