arXiv subjects

Luis A. Escamilla

Publications and source records attributed to Luis A. Escamilla.

27 records · Page 2Linked to original sources

arXiv2024

Multidimensionality of the Hubble tension: the roles of $Ω_m$ and $ω_c$

The Hubble tension is inherently multidimensional, and bears important implications for parameters beyond $H_0$. We discuss the key role of the matter density parameter $Ω_m$ and the physical cold dark matter density $ω_c$. We argue that once $Ω_m$ and the physical baryon density $ω_b$ are calibrated, through Baryon Acoustic Oscillations (BAO) and/or Type Ia Supernovae (SNeIa) for $Ω_m$, and via Big Bang Nucleosynthesis for $ω_b$, any model raising $H_0$ requires raising $ω_c$ and, under minimal assumptions, also the clustering parameter $S_8$. We explicitly verify that this behaviour holds when analyzing recent BAO and SNeIa data. We argue that a calibration of $Ω_m$ as reliable and model-independent as possible should be a priority in the Hubble tension discussion, and an interesting possibility in this sense could be represented by galaxy cluster gas mass fraction measurements.

astro-ph.CO↗

arXiv2024

Do we need wavelets in the late Universe?

We parameterize the Hubble function by adding Hermitian wavelets to the Hubble radius of $Λ$CDM. This allows us to build Hubble functions that oscillate around $Λ$CDM at late times without modifying its angular diameter distance to last scattering. We perform parameter inference and model selection procedures on these new Hubble functions at the background level. In our analyses consisting of a wide variety of cosmological observations, we find that baryon acoustic oscillations (BAO) data play a crucial role in determining the constraints on the wavelet parameters. In particular, we focus on the differences between SDSS- and DESI-BAO datasets and find that wavelets provide a better fit to the data when either of the BAO datasets is present. However, DESI-BAO has a preference for the center of the wavelets to be around $z \sim 0.7$, while SDSS-BAO prefers higher redshifts of $z > 1$. This difference appears to be driven by the discrepancies between these two datasets in their $D_H / r_{\rm d}$ measurements at $z = 0.51$ and $z \sim 2.3$. Finally, we also derive the consequences of the wavelets on a dark energy component. We find that the dark energy density oscillates by construction and also attains negative values at large redshifts ($z\gtrsim2$) as a consequence of the SDSS-BAO data. We conclude that while the early universe and the constraints on the matter density and the Hubble constant remain unchanged, wavelets are favored in the late universe by the BAO data. Specifically, there is a significant improvement at more than $3σ$ in the fit when new DESI-BAO data are included in the analysis.

astro-ph.CO↗

arXiv2024

Exploring the Hubble tension with a late time Modified Gravity scenario

We investigate a modified cosmological model aimed at addressing the Hubble tension, considering revised dynamics in the late Universe. The model introduces a parameter $c$ affecting the evolution equations, motivated by a modified Poisson algebra inspired by effective Loop Quantum Cosmology. Our analysis includes diverse background datasets such as Cosmic Chronometers, Pantheon+ Type Ia Supernovae (with and without the SH0ES calibration), SDSS, DESY6 and DESI Baryon Acoustic Oscillations, and background information of the Cosmic Microwave Background. We find that the model alleviates the Hubble tension in most of the dataset combinations, with cases reducing discrepancies to below $1σ$ when including SH0ES. However, the model exhibits minimal improvement in the overall fit when compared to $Λ$CDM, and Bayesian evidence generally favors the standard model. Theoretical foundations support this approach as a subtle adjustment to low-redshift dynamics, suggesting potential for further exploration into extensions of $Λ$CDM. Despite challenges in data fitting, our findings underscore the promise of small-scale modifications in reconciling cosmological tensions.

astro-ph.CO↗

arXiv2024

The state of the dark energy equation of state circa 2023

We critically examine the state of current constraints on the dark energy (DE) equation of state (EoS) $w$. Our study is motivated by the observation that, while broadly consistent with the cosmological constant value $w=-1$, several independent probes appear to point towards a slightly phantom EoS ($w \sim -1.03$) which, if confirmed, could have important implications for the Hubble tension. We pay attention to the apparent preference for phantom DE from Planck Cosmic Microwave Background (CMB) data alone, whose origin we study in detail and attribute to a wide range of (physical and geometrical) effects. We deem the combination of Planck CMB, Baryon Acoustic Oscillations, Type Ia Supernovae, and Cosmic Chronometers data to be particularly trustworthy, inferring from this final consensus dataset $w=-1.013^{+0.038}_{-0.043}$, in excellent agreement with the cosmological constant value. Overall, despite a few scattered hints, we find no compelling evidence forcing us away from the cosmological constant (yet).

astro-ph.CO↗

arXiv2023

Model-independent reconstruction of the Interacting Dark Energy Kernel: Binned and Gaussian process

The cosmological dark sector remains an enigma, offering numerous possibilities for exploration. One particularly intriguing option is the (non-minimal) interaction scenario between dark matter and dark energy. In this paper, to investigate this scenario, we have implemented Binned and Gaussian model-independent reconstructions for the interaction kernel alongside the equation of state; while using data from BAOs, Pantheon+ and Cosmic Chronometers. In addition to the reconstruction process, we conducted a model selection to analyze how our methodology performed against the standard $Λ$CDM model. The results revealed a slight indication, of at least 1$σ$ confidence level, for some oscillatory dynamics in the interaction kernel and, as a by-product, also in the DE and DM. A consequence of this outcome is the possibility of a sign change in the direction of the energy transfer between DE and DM and a possible transition from a negative DE energy density in early-times to a positive one at late-times. While our reconstructions provided a better fit to the data compared to the standard model, the Bayesian Evidence showed an intrinsic penalization due to the extra degrees of freedom. Nevertheless these reconstructions could be used as a basis for other physical models with lower complexity but similar behavior.

astro-ph.CO↗

arXiv2023

Cosmology on a Gravitational Wave Background

It is a fact that the universe lives on a Gravitational Wave Background (GWB), which it may be in the form of extra energy, which is not contained in Einstein's field equations. In \cite{Matos:2021jef}, a new model was developed to explain the current accelerating expansion of the universe where a GWB was incorporated by extending Einstein's equations to $R_{μν}-\frac{1}{2}Rg_{μν}+\frac{2π^2}{λ^2}g_{μν}=κ^2 T_{μν}$, where $λ$ is the Compton wavelength of the graviton. In the present work we show that this extended form agrees very well with the observations of Cosmic chronometers, Baryon Acoustic Oscillations and Pantheon SN type Ia, reproducing the observational data with a $Δχ^2=3.26$ in favor of the present model compared to the $Λ$CDM. The values favored by these observations are $Ω_{\rm m} = 0.31 \pm 0.02$, $H_0=68 \pm 0.02$ Km/s/Mpc, $Ω_{\rm k} = 0.001\pm 0.011$; we also find an excellent consistence of this model with the Cosmic Microwave Background and the Matter Power Spectrum. We conclude that this model is an excellent alternative to explain the accelerating expansion of the universe without incorporating the cosmological constant.

physics.gen-ph↗

arXiv2023

Model selection applied to reconstructions of the Dark Energy

The main aim of this paper is to perform a model comparison for some reconstructions of the key properties that describe the dark energy of the Universe i.e. energy density and the equation of state (EoS). We carry out this process by using a binning and a linear interpolation methodologies, and on top of that, we incorporate a correlation function mechanism. An extension of the two of them was also introduced, where internal amplitudes are allowed to vary in height as well as in position. The reconstructions were made with data from the Hubble parameter, Supernovae Type Ia and Baryon Acoustic Oscillations (H+SN+BAO), all of which span a range from $z=0.01$ to $z=2.34$. First we perform the parameter estimation for each of the reconstructions to then provide a model selection through the Bayesian Evidence. Throughout our process we found a better fit to the data, up to $4σ$ compared to $Λ$CDM, and the presence of some interesting features, i.e. an oscillatory behaviour at late times, a decrease in the dark energy density component at early times and a transition to the phantom divide-line in the EoS. To discern these features from noisy contributions, we include a principal component analysis and found that some of these characteristics should be taken into account to satisfy current observations.

astro-ph.CO↗

arXiv2021

Cosmological parameter inference with Bayesian statistics

Bayesian statistics and Markov Chain Monte Carlo (MCMC) algorithms have found their place in the field of Cosmology. They have become important mathematical and numerical tools, especially in parameter estimation and model comparison. In this paper, we review some fundamental concepts to understand Bayesian statistics and then introduce MCMC algorithms and samplers that allow us to perform the parameter inference procedure. We also introduce a general description of the standard cosmological model, known as the $Λ$CDM model, along with several alternatives, and current datasets coming from astrophysical and cosmological observations. Finally, with the tools acquired, we use an MCMC algorithm implemented in python to test several cosmological models and find out the combination of parameters that best describes the Universe.

astro-ph.CO↗

arXiv2020

Graduated dark energy: Observational hints of a spontaneous sign switch in the cosmological constant

We study the cosmological constant ($Λ$) in the standard $Λ$CDM model by introducing the \textit{graduated dark energy} (gDE) characterised by a minimal dynamical deviation from the null inertial mass density of the $Λ$ in the form $ρ_{\rm inert}\propto ρ^λ<0$ with $λ<1$ being a ratio of two odd integers, for which its energy density $ρ$ dynamically takes negative values in the finite past. For large negative values of $λ$, it creates a phenomenological model described by a smooth function that approximately describes the $Λ$ spontaneously switching sign in the late universe to become positive today. We confront the model with the latest combined observational data sets of PLK+BAO+SN+$H$. It is striking that the data predict bimodal posterior probability distributions for the parameters of the model along with large negative $λ$ values; the new maximum significantly excludes the $Λ$, and the old maximum contains the $Λ$. The improvement in the goodness of fit for the $Λ$ reaches highly significant levels, $Δχ_{\rm min}^2=6.4$ for the new maxima, while it remains at insignificant levels, $Δχ_{\rm min}^2\lesssim0.02$, for the old maxima. We show that, in contrast to the old maxima, which do not distinguish from the $Λ$, the new maxima agree with the model-independent $H_0$ measurements, high-precision Ly-$α$ data, and model-independent $Omh^2$ diagnostic estimates. Our results provide strong hints of a spontaneous sign switch in the cosmological constant and lead us to conjecture that the universe has transitioned from AdS vacua to dS vacua, at a redshift $z\approx 2.32$ and triggered the late-time acceleration, and suggests looking for such mechanisms in string theory constructions.

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