Searcharxiv⌕ Search

arXiv subjects

Ismael Tereno

Publications and source records attributed to Ismael Tereno.

18 recordsLinked to original sources
arXiv2026

Testing cosmological structure formation in a Unified Dark Matter-Energy model with fast transition

Unified Dark Matter-Energy models (UDM), a class of models where dark matter and dark energy exist as a single cosmological fluid, are an alternative approach to $\Lambda$CDM. In this work we focus on a model with a fast transition between dark matter-like and dark energy-like behaviour. The epoch and rapidity of the transition are the key features to enable the formation of structure in this model. We have studied its viability using CMB and Weak Lensing data with nested sampling inference methods. We found that the preferred region of the parameter space is the one with early and fast transition models, where it also lies the model's $\Lambda$CDM limit. Our study confirms that this UDM model is able to form cosmological structure compatible with the data used.

astro-ph.CO↗
arXiv2023

Is there evidence for CIDER in the Universe?

In this work we analyze the full linear behaviour of the constrained interacting dark energy (CIDER) model, which is a conformally coupled quintessence model tailored to mimic a $Λ$CDM expansion. We compute the matter and temperature anisotropies power spectra and test the model against recent observational data. We shed light on some particular subtleties of the background behaviour that were not fully captured in previous works, and study the physics of the linear cosmological observables. One novelty found was that matter perturbations are enhanced at large scales when compared with the ones of the standard $Λ$CDM. The reason and impact of this trend on the cosmological observables and on the physics of the early Universe are considered. We find that the introduction of the coupling parameter alleviates the $σ_8$ tension between early and late time probes although Planck data favours the $Λ$CDM limit of the model.

astro-ph.CO↗
arXiv2019

Minkowski Functionals of Convergence Maps and the Lensing Figure of Merit

Minkowski functionals (MFs) quantify the topological properties of a given field probing its departure from Gaussianity. We investigate their use on lensing convergence maps in order to see whether they can provide further insights on the underlying cosmology with respect to the standard second-order statistics, i.e., cosmic shear tomography. To this end, we first present a method to match theoretical predictions with measured MFs taking care of the shape noise, imperfections in the map reconstruction, and inaccurate description of the nonlinearities in the matter power spectrum and bispectrum. We validate this method against simulated maps reconstructed from shear fields generated by the MICE simulation. We then perform a Fisher matrix analysis to forecast the accuracy on cosmological parameters from a joint MFs and shear tomography analysis. It turns out that MFs are indeed helpful to break the $Ω_{\rm m}$--$σ_8$ degeneracy thus generating a sort of chain reaction leading to an overall increase of the Figure of Merit.

astro-ph.CO↗
arXiv2017

Cosmological constraints on a unified dark matter-energy scalar field model with fast transition

We test the viability of a single fluid cosmological model containing a transition from a dark-matter-like regime to a dark-energy-like regime. The fluid is a k-essence scalar field with a well-defined Lagrangian. We constrain its model parameters with a combination of geometric probes and conclude that the evidence for this model is similar to the evidence for $Λ$CDM. In addition, we find a lower bound for the rapidity of the transition, implying that fast transitions are favored with respect to slow ones even at background level.

astro-ph.CO↗
arXiv2017

Theia: Faint objects in motion or the new astrometry frontier

In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision.

astro-ph.IM↗
arXiv2016

Unveiling the Dynamics of the Universe

We explore the dynamics and evolution of the Universe at early and late times, focusing on both dark energy and extended gravity models and their astrophysical and cosmological consequences. Modified theories of gravity not only provide an alternative explanation for the recent expansion history of the universe, but they also offer a paradigm fundamentally distinct from the simplest dark energy models of cosmic acceleration. In this review, we perform a detailed theoretical and phenomenological analysis of different modified gravity models and investigate their consistency. We also consider the cosmological implications of well motivated physical models of the early universe with a particular emphasis on inflation and topological defects. Astrophysical and cosmological tests over a wide range of scales, from the solar system to the observable horizon, severely restrict the allowed models of the Universe. Here, we review several observational probes -- including gravitational lensing, galaxy clusters, cosmic microwave background temperature and polarization, supernova and baryon acoustic oscillations measurements -- and their relevance in constraining our cosmological description of the Universe.

astro-ph.CO↗
arXiv2016

Constraining $f(T, \mathcal{T})$ gravity models using type Ia supernovae

We present an analysis of an $f(T, \mathcal{T})$ extension of the Teleparallel Equivalent of General Relativity, where $T$ denotes the torsion and $\mathcal{T}$ the trace of the energy-momentum tensor. This extension includes non--minimal couplings between torsion and matter. In particular, we construct two specific models that recover the usual continuity equation, namely, $f(T, \mathcal{T})=T+g(\mathcal{T})$ and $f(T, \mathcal{T})=T\times g(\mathcal{T})$. We then constrain the parameters of each model by fitting the predicted distance modulus to that measured from type Ia supernovae, and find that both models can reproduce the late--time cosmic acceleration. We also observe that one of the models satisfies well the observational constraints and yields a goodness--of--fit similar to the $Λ$CDM model, thus demonstrating that $f(T,\mathcal{T})$ gravity theory encompasses viable models that can be an alternative to $Λ$CDM.

gr-qc↗
arXiv2016

Beyond $Λ$CDM: Problems, solutions, and the road ahead

Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, $Λ$CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of $Λ$CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.

astro-ph.CO↗
arXiv2013

CMB lensing reconstruction from the WMAP 7-year data

We attempt to make a direct measurement of the weak lensing signal from the WMAP 7-year data. We apply the real-space implementation of the optimal quadratic estimator on the maps produced by the W-band Differencing Assemblies. We obtain a weak lensing amplitude parameter of $A_{L}=0.99\pm1.67$ after correcting for several sources of bias. The error budget includes a contribution from the bias removal procedure. Despite the demonstrated insensitivity of the real-space estimator to uncorrelated noise, we conclude that this detection is not statistically significant. We expect that a full-sky, higher-sensitivity experiment such as Planck will allow us to make a more significant measurement.

astro-ph.CO↗
arXiv2011

Measurement of halo properties with weak lensing shear and flexion

We constrain properties of cluster haloes by performing likelihood analysis using lensing shear and flexion data. We test our analysis using two mock cluster haloes: an isothermal ellipsoid (SIE) model and a more realistic elliptical Navarro-Frenk-White (eNFW) model. For both haloes, we find that flexion is more sensitive to the halo ellipticity than shear. The introduction of flexion information significantly improves the constraints on halo ellipticity, orientation and mass. We also point out that there is a degeneracy between the mass and the ellipticity of SIE models in the lensing signal.

astro-ph.CO↗
arXiv2011

CMB lensing reconstruction with point source masks

An incomplete sky coverage poses difficulties in the extraction of the weak lensing information from the CMB. We test the reconstruction of the weak lensing convergence from CMB maps to which masks of point sources have been applied. We use the quadratic estimator with a kernel with finite support acting in real space for a Planck simulation. We recover the lensing signal without significant loss of power or addition of spurious correlations, thus showing that masking defected pixels does not affect the reconstruction of the weak lensing convergence in real space.

astro-ph.CO↗
arXiv2010

COSMOS weak-lensing constraints on modified gravity

The observed acceleration of the universe, explained through dark energy, could alternatively be explained through a modification of gravity that would also induce modifications in the evolution of cosmological perturbations. We use new weak lensing data from the COSMOS survey to test for deviations from General Relativity. The departure from GR is parametrized in a model-independent way that consistently parametrizes the two-point cosmic shear amplitude and growth. Using CMB priors, we perform a likelihood analysis. We find constraints on the amplitude of the signal that do not indicate a deviation from General Relativity.

astro-ph.CO↗
arXiv2009

CFHTLS weak-lensing constraints on the neutrino masses

We use measurements of cosmic shear from CFHTLS, combined with WMAP-5 cosmic microwave background anisotropy data, baryonic acoustic oscillations from SDSS and 2dFGRS and supernovae data from SNLS and Gold-set, to constrain the neutrino mass. We obtain a 95% confidence level upper limit of 0.54 eV for the sum of the neutrino masses, and a lower limit of 0.03 eV. The preference for massive neutrinos vanishes when shear-measurement systematics are included in the analysis.

astro-ph↗
arXiv2008

Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias

The current methods available to estimate gravitational shear from astronomical images of galaxies introduce systematic errors which can affect the accuracy of weak lensing cosmological constraints. We study the impact of KSB shape measurement bias on the cosmological interpretation of tomographic two-point weak lensing shear statistics. We use a set of realistic image simulations produced by the STEP collaboration to derive shape measurement bias as a function of redshift. We define biased two-point weak lensing statistics and perform a likelihood analysis for two fiducial surveys. We present a derivation of the covariance matrix for tomography in real space and a fitting formula to calibrate it for non-Gaussianity. We find the biased aperture mass dispersion is reduced by ~20% at redshift ~1, and has a shallower scaling with redshift. This effect, if ignored in data analyses, biases sigma_8 and w_0 estimates by a few percent. The power of tomography is significantly reduced when marginalising over a range of realistic shape measurement biases. For a CFHTLS-Wide-like survey, [Omega_m, sigma_8] confidence regions are degraded by a factor of 2, whereas for a KIDS-like survey the factor is 3.5. Our results are strictly valid only for KSB methods but they demonstrate the need to marginalise over a redshift-dependent shape measurement bias in all future cosmological analyses.

astro-ph↗
arXiv2006

Scalar-field quintessence by cosmic shear: CFHT data analysis and forecasts for DUNE

A light scalar field, minimally or not-minimally coupled to the metric field, is a well-defined candidate for the dark energy, overcoming the coincidence problem intrinsic to the cosmological constant and avoiding the difficulties of parameterizations. We present a general description of the weak gravitational lensing valid for every metric theory of gravity, including vector and tensor perturbations for a non-flat spatial metric. Based on this description, we investigate two minimally-coupled scalar field quintessence models using VIRMOS-Descart and CFHTLS cosmic shear data, and forecast the constraints for the proposed space-borne wide-field imager DUNE.

astro-ph↗
arXiv2006

Tracking quintessence by cosmic shear - Constraints from VIRMOS-Descart and CFHTLS and future prospects

Dark energy can be investigated in two complementary ways, by considering either general parameterizations or physically well-defined models. Following the second route, we explore the constraints on quintessence models where the acceleration is driven by a slow-rolling scalar field. The analysis focuses on cosmic shear, combined with supernovae Ia and CMB data. Using a Boltzmann code including quintessence models and the computation of weak lensing observables, we determine several two-point shear statistics. The non-linear regime is described by two different mappings. The likelihood analysis is based on a grid method. The data include the "gold set" of supernovae Ia, the WMAP-1 year data and the VIRMOS-Descart and CFHTLS-deep and -wide data for weak lensing. This is the first analysis of high-energy motivated dark energy models that uses weak lensing data. We explore larger angular scales, using a synthetic realization of the complete CFHTLS-wide survey as well as next space-based missions surveys. Two classes of cosmological parameters are discussed: i) those accounting for quintessence affect mainly geometrical factors; ii) cosmological parameters specifying the primordial universe strongly depend on the description of the non-linear regime. This dependence is addressed using wide surveys, by discarding the smaller angular scales to reduce the dependence on the non-linear regime. Special care is payed to the comparison of these physical models with parameterizations of the equation of state. For a flat universe and a quintessence inverse power law potential with slope alpha, we obtain alpha < 1 and Omega_Q=0.75^{+0.03}_{-0.04} at 95% confidence level, whereas alpha=2^{+18}_{-2}, Omega_Q=0.74^{+0.03}_{-0.05} when including supergravity corrections.

astro-ph↗
arXiv1999

Velocity at the Schwarzschild horizon revisited

The question of the physical reality of the black hole interior is a recurrent one. An objection to its existence is the well known fact that the velocity of a material particle, refered to the stationary frame, tends to the velocity of light as it approaches the horizon. It is shown, using Kruskal coordinates, that a timelike radial geodesic does not become null at the event horizon.

astro-ph↗