arXiv subjects

Elsa M. Teixeira

Publications and source records attributed to Elsa M. Teixeira.

At least 19 recordsLinked to original sources

arXiv2026

Peering Beyond the Veil of Last Scattering: A View of the Universe with CMB Spectral Distortions

The frequency spectrum of the cosmic microwave background is the most precise blackbody ever measured in nature, with deviations constrained at the level of almost one part per million from the COBE satellite. Nevertheless, departures away from a perfect blackbody are present in standard $Λ$CDM cosmology, lurking just beneath the surface of our current observational bounds. These spectral distortions provide invaluable information on our thermal history in both the post- and pre-recombination epochs, allowing us to peer beyond last scattering and into the primordial Universe. Here, we present an overview of the underlying physics responsible for generating CMB spectral distortions at all epochs. As an illustration of this rich physics, we review a comprehensive set of mechanisms capable of generating distortions both within and beyond the standard $Λ$CDM paradigm. We also discuss the information that can be gleaned by going beyond the monopole (sky-averaged) spectrum and exploiting the spatial information present in anisotropic spectral distortions. To supplement our discussion of the diverse science of spectral distortions, we provide an overview of the upcoming and proposed experimental landscape. We highlight that the combination of the TMS, COSMO, and BISOU experiments will provide the first discovery of a monopole $y$-type distortion within the coming decade. From space, the proposed FOSSIL experiment is forecasted to improve upon the original COBE/FIRAS measurement by roughly three orders of magnitude in sensitivity, bringing with it the detection of the $Λ$CDM $μ$-type distortion sourced by the dissipation of small scale acoustic modes in the pre-recombination plasma. With transformational measurements on the horizon, CMB spectral distortions offer a uniquely sensitive probe of the thermal history of the Universe at redshifts $z \lesssim 2 \times 10^6$.

astro-ph.CO↗

arXiv2026

The road towards precision measurements of $H_0$ with bright sirens in the Einstein Telescope era

Gravitational-wave standard sirens provide an independent probe of cosmic expansion since their luminosity distances are inferred directly from the gravitational-wave signal and, for bright sirens (BSs), the source redshifts are obtained through the identification of electromagnetic counterparts. In this work, we forecast the constraining power of future bright siren catalogues on the Hubble constant using simulated binary-neutron-star mergers detected by the Einstein Telescope with associated electromagnetic counterparts. We construct mock catalogues with different numbers of events and redshift distributions, with GW170817 as a reference BS, and analyse the resulting constraints within a flat $Λ$CDM cosmology. We find that, when bright sirens are used as a standalone probe, most of the information on $H_0$ is provided by low-redshift events, with the improvement in precision saturating for sources above $z \sim 1$; beyond that redshift, the constraining power of BSs is increasingly limited by the degeneracy with $Ω_m$, which prevents further gains in precision on $H_0$. In this case, approximately $90$ low-redshift BSs are required to reach $σ_{H_0} \sim 1\,{\rm km\,s^{-1}\,Mpc^{-1}}$, while about $45$ are sufficient for $σ_{H_0} \sim 2\,{\rm km\,s^{-1}\,Mpc^{-1}}$. When external BAO information is included to reduce the $H_0 - Ω_m$ degeneracy, intermediate-redshift sirens become more informative and the required number of events decreases substantially, to roughly $20$ and $15$ BSs for $σ_{H_0} \sim 1\,{\rm km\,s^{-1}\,Mpc^{-1}}$ and $σ_{H_0} \sim 2\,{\rm km\,s^{-1}\,Mpc^{-1}}$, respectively. These results highlight the importance of both electromagnetic counterpart identification and complementary background probes in making BSs a competitive, distance-ladder-independent test of the Hubble tension.

astro-ph.CO↗

arXiv2026

Interacting dark sector from intrinsic entropy couplings

We introduce a new class of interacting dark sector models that couple the intrinsic entropy of dark matter to scalar field dark energy. Using the Lagrangian formulation for relativistic perfect fluids, we construct consistent covariant actions that incorporate algebraic and derivative entropy couplings. These interactions leave the expansion history unchanged, rendering the background cosmology indistinguishable from $Λ$CDM or uncoupled quintessence. At the level of cosmological perturbations, the entropy couplings generate scale-dependent modifications to the dark matter Euler equation, while the continuity equation remains unaltered at linear order. The resulting interactions correspond to a pure-momentum exchange within the dark sector. We show that intrinsic entropy perturbations can carry primordial scale dependence, and non-minimal couplings can lead to a scale-dependent suppression or enhancement of structure growth. Finally, we demonstrate that these models are generically compatible with current Cosmic Microwave Background observations, while inducing distinctive signatures in large-scale structure. The framework provides a theoretically well-motivated and observationally viable extension to the standard cosmological model, opening new directions to explore novel interactions in the dark sector.

astro-ph.CO↗

arXiv2026

Interactions in the dark sector: intrinsic entropy couplings

We present a new class of interacting dark sector models in which the intrinsic entropy of a dark matter fluid couples to a scalar field describing dark energy. These interactions are constructed within a covariant Lagrangian framework, including algebraic and derivative entropy couplings, effectively leading to pure momentum exchange in the dark sector. A key feature is that the background cosmology remains unchanged and therefore indistinguishable from $Λ$CDM or uncoupled quintessence. However, at the level of the linear perturbations, the dark matter Euler equation exhibits scale-dependent contributions, while the continuity equation is unmodified. We show that these classes of models are compatible with current CMB constraints and can potentially produce observable signatures in large-scale structure.

astro-ph.CO↗

arXiv2025

Deciphering Coupled Scalar Dark Sectors

Coupled dark sector models have gained significant attention, motivated by recent advances in cosmology and the pressing need to address unresolved puzzles. In this work, we study coupled scalar dark sector models inspired by ultraviolet-complete frameworks such as supergravity and string theory. These models involve scalar couplings arising either from their kinetic terms, through a non-trivial field space metric, or from their scalar potential. We demonstrate how these couplings can be elegantly formulated in terms of an interacting vector, a standard tool in coupled dark sector studies, and analyse their distinct cosmological effects using a dynamical systems approach. Using this framework, we further investigate an axio-dilaton system recently explored in the literature, where the dilaton also couples to baryons. Intriguingly, we show that certain kinetic and potential interactions may mimic one another or even cancel out, making them observationally indistinguishable. If such a distinction becomes possible through observational constraints, it could provide valuable insights into the underlying field space metric and its connection to fundamental physics.

hep-th↗

arXiv2025

A frequentist view on the two-body decaying dark matter model

Decaying dark matter (DDM) has emerged as an interesting framework to extend the $Λ$-cold-dark-matter (LCDM) model, as many particle physics models predict that dark matter may not be stable over cosmic time and can impact structure formation. In particular, a model in which DDM decays at a rate $Γ$ and imprints a velocity kick $v$ onto its decay products leads to a low amplitude of fluctuations, as quantified by the parameter $S_8$, in better agreement with that measured by some weak lensing surveys. Bayesian analyses have provided mixed conclusions regarding its viability, with a reconstructed clustering amplitude only slightly below the standard LCDM value. In this paper, we contrast previous results with a frequentist analysis of Planck and SDSS BAO data. We find that the $68\%$ confidence level region corresponds to a decay half-life of $6.93^{+7.88}_{-2.85}$Gyr and a velocity kick of $1250^{+1450}_{-1000}$~km/s. These $1σ$ constraints strongly differ from their Bayesian counterparts, indicating the presence of volume effect in the Bayesian analysis. Moreover, we find that under the DDM model, the frequentist analysis predicts lower values of $S_8$, in agreement with those found by KiDS-1000 and DES-Y3 at $\sim 1.5σ$. We further show that previously derived KiDS-1000 constraints that appeared to exclude the best-fit model from Planck data were driven by priors on the primordial amplitude $A_s$ and spectral index $n_s$. When those are removed from the analysis, KiDS-1000 constraints on the DDM parameters are fully relaxed. It is only when applying Planck-informed priors on $A_s$ and $n_s$ to the KiDS-1000 analysis that one can constrain the model. We note that without such priors, the scales best measured by KiDS-1000 do not exactly match the $S_8$ kernel, so $S_8$ constraints should not be applied directly to a model in place of the full likelihood.

astro-ph.CO↗

arXiv2025

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

astro-ph.CO↗

arXiv2025

Resilience and implications of adiabatic CMB cooling

We investigate potential deviations from the standard adiabatic evolution of the cosmic microwave background (CMB) temperature, $T_{\rm CMB}(z)$, using the latest Sunyaev-Zeldovich (SZ) effect measurements and molecular line excitation data, covering a combined redshift range of $0 < z \lesssim 6$. We follow different approaches. First, we reconstruct the redshift evolution of $T_{\rm CMB}(z)$ in a model-independent way using Gaussian Process regression. The tightest constraints come from SZ measurements at $z < 1$, while molecular line data at $z > 3$ yield broader uncertainties. By combining both datasets, we find good consistency with the standard evolution across the full analysed redshift range, inferring a present-day CMB monopole temperature of $T_0 = 2.744 \pm 0.019$ K. Next, we test for deviations from the standard scaling by adopting the parameterisation $T_{\rm CMB}(z) = T_0(1+z)^{1-β}$, where $β$ quantifies departures from adiabaticity, with $β= 0$ corresponding to the standard scenario. In this framework, we use Gaussian Process reconstruction to test the consistency of $β= 0$ across the full redshift range and perform $χ^2$ minimisation techniques to determine the best-fit values of $T_0$ and $β$. In both cases, we find good consistency with the standard temperature-redshift relation. The $χ^2$-minimisation analysis yields best-fit values of $β= -0.0106 \pm 0.0124$ and $T_0 = 2.7276 \pm 0.0095$ K, in excellent agreement with both $β= 0$ and independent direct measurements of $T_0$ from FIRAS and ARCADE. We discuss the implications of our findings, which offer strong empirical support for the standard cosmological prediction and place tight constraints on a wide range of alternative scenarios of interest in the context of cosmological tensions and fundamental physics.

astro-ph.CO↗

arXiv2025

Implications of distance duality violation for the $H_0$ tension and evolving dark energy

We investigate whether a violation of the distance duality relation (DDR), $D_L(z) = (1+z)^2 D_A(z)$, connecting the angular diameter and luminosity distances, can explain the Hubble tension and alter the evidence for dynamical dark energy in recent cosmological observations. We constrain five phenomenological parameterisations of DDR violation using Baryon Acoustic Oscillation measurements from the DESI survey calibrated with the sound horizon derived from \textit{Planck} Cosmic Microwave Background data and the Pantheon+ Type Ia supernova (SNIa) catalogue calibrated with the supernova absolute magnitude from S$H_0$ES. We find that two toy models can resolve the tension: a constant offset in the DDR (equivalent to a shift in the calibration of the SNIa data), $D_L(z)/D_A(z)\simeq 0.925(1+z)^2$, which leaves the hint for evolving dark energy unaffected; or a change in the power-law redshift-dependence of the DDR, restricted to $z\lesssim 1$, $D_L(z)/D_A(z)\simeq(1+z)^{1.866}$, together with a {\it constant} phantom dark energy equation of state $w\sim -1.155$. The Bayesian evidence slightly favours the latter model. Our phenomenological approach motivates the investigation of physical models of DDR violation as a novel way to explain the Hubble tension.

astro-ph.CO↗

arXiv2025

Self-interacting neutrinos in light of recent CMB and LSS data

We update constraints on a simple model of self-interacting neutrinos involving a heavy scalar mediator with universal flavor coupling. According to past literature, such a model is allowed by Cosmic Microwave Background (CMB) data, with some CMB and large-scale structure data even favoring a strongly-interacting neutrino (SI$ν$) scenario over $Λ$CDM. In this work, we re-evaluate the constraints on this model in light of the new Planck NPIPE data, DESI BAO data, and the Effective Field Theory of Large Scale Structures (EFTofLSS) applied to BOSS data. We find that Planck NPIPE are more permissive to the SI$ν$ scenario and that DESI data favor the SI$ν$ over $Λ$CDM. However, when considering EFTofBOSS data, this mode is no longer preferred. Therefore, new DESI data analyzed under the EFTofLSS are particularly awaited to shed light on this disagreement.

astro-ph.CO↗

arXiv2024

Alleviating cosmological tensions with a hybrid dark sector

We investigate a cosmological model inspired by hybrid inflation, where two scalar fields representing dark energy (DE) and dark matter (DM) interact through a coupling that is proportional to the DE scalar field $1/ϕ$. The strength of the coupling is governed solely by the initial condition of the scalar field, $ϕ_i$, which parametrises deviations from the standard $Λ$CDM model. In this model, the scalar field tracks the behaviour of DM during matter-domination until it transitions to DE while the DM component decays quicker than standard CDM during matter-domination, and is therefore different from some interacting DM-DE models which behaves like phantom dark energy. Using \textit{Planck} 2018 CMB data, DESI BAO measurements and Pantheon+ supernova observations, we find that the model allows for an increase in $H_0$ that can help reduce the Hubble tension. In addition, we find that higher values of the coupling parameter are correlated with lower values of $ω_m$, and a mild decrease of the weak-lensing parameter $S_8$, potentially relevant to address the $S_8$ tension. Bayesian model comparison, however, reveals inconclusive results for most datasets, unless S$H_0$ES data are included, in which case a moderate evidence in favour of the hybrid model is found.

astro-ph.CO↗

arXiv2024

Scalar field dark matter with time-varying equation of state

We propose a new model of scalar field dark matter interacting with dark energy. Adopting a fluid description of the dark matter field in the regime of rapid oscillations, we find that the equation of state for dark matter is non-zero and even becomes increasingly negative at late times during dark energy domination. Furthermore, the speed of sound of dark matter is non-vanishing at all length scales, and a non-adiabatic pressure contribution arises. The results indicate that there are still unexplored possible interactions within the dark sector that lead to novel background effects and can impact structure formation processes.

astro-ph.CO↗

arXiv2024

Illuminating the Dark Sector: Searching for new interactions between dark matter and dark energy

The current standard model of cosmology - the {\ensuremathΛ}CDM model - is appropriately named after its controversial foreign ingredients: a cosmological constant ({\ensuremathΛ}) that accounts for the recent accelerated expansion of the Universe and cold dark matter needed to explain the formation and dynamics of large scale structures. Together, these form the dark sector, whose nature remains a mystery. After 25 years of withstanding confirmation and support for the {\ensuremathΛ}CDM model, enough to bypass some of its unclear theoretical issues, this paradigm is facing its biggest crisis yet. The rapid advent of technology has brought cosmology to an unprecedented observational era, with increased technical precision and the emergence of independent measures, including probes of phenomena that were thought impossible to detect or even exist, such as the gravitational ripples that propagate in the spacetime. However, such precision has unveiled cracks in the porcelain of {\ensuremathΛ}CDM, with pieces that seem glued together and difficult to reconcile. Particularly worrying is the apparent lack of compatibility between measurements of the Universe's present expansion rate based on local measurements and those based on phenomena that occurred far in the early Universe and that can only be translated into present quantities through physical propagation under a cosmological model. In this dissertation, we delve into extensions to the standard model that consider alternatives to the mysterious nature of the dark sector and any possible new interactions therein. We analyse these alternative models, hoping to identify measurable observational signatures of extra degrees of freedom in the dark sector.

astro-ph.CO↗

arXiv2023

Forecasts on interacting dark energy with standard sirens

We present the predictions with standard sirens at Gravitational Waves detectors, such as the Laser Interferometer Space Antenna (LISA) and the Einstein Telescope (ET), for interacting dark energy theories. We focus on four models characterised by couplings between the dark energy field and the dark matter fluid arising from conformal or disformal transformations of the metric, along with an exponential self-interacting potential. To this purpose we construct mock catalogues and perform a Markov Chain Monte Carlo analysis by considering ET and LISA standard sirens, and also their combination with Baryon Acoustic Oscillations (BAO) and Supernovae Ia (SNIa) data. We find that in all the four models considered, the accuracy on the $H_0$ parameter increases by one order of magnitude at 1$σ$ when compared to the SNIa+BAO data set, possibly shedding light in the future on the origin of the $H_0$-tension. The combination of standard sirens with SNIa+BAO allows to improve the accuracy on some coupling and exponential parameters, hinting at future prospects for constraining interactions in the dark sector.

astro-ph.CO↗

arXiv2023

Scalar field dark matter and dark energy: a hybrid model for the dark sector

Diverse cosmological and astrophysical observations strongly hint at the presence of dark matter and dark energy in the Universe. One of the main goals of Cosmology is to explain the nature of these two components. It may well be that both dark matter and dark energy have a common origin. In this paper, we develop a model in which the dark sector arises due to an interplay between two interacting scalar fields. Employing a hybrid inflation potential, we show that the model can be described as a system of a pressureless fluid coupled to a light scalar field. We discuss this setup's cosmological consequences and the observational signatures in the cosmic microwave background radiation and the large-scale structures.

hep-th↗

arXiv2022

Dissecting kinetically coupled quintessence: phenomenology and observational tests

We investigate an interacting dark energy model which allows for the kinetic term of the scalar field to couple to dark matter via a power-law interaction. The model is characterised by scaling solutions at early times, which are of high interest to alleviate the coincidence problem, followed by a period of accelerated expansion. We discuss the phenomenology of the background evolution and of the linear scalar perturbations and we identify measurable signatures of the coupling in the dark sector on the cosmic microwave background, the lensing potential auto-correlation and the matter power spectra. We also perform a parameter estimation analysis using data of cosmic microwave background temperature, polarisation and lensing, baryonic acoustic oscillations and supernovae. We find that the strength of the coupling between the dark sectors, regulated by the parameter $α$, is constrained to be of order $10^{-4}$. A model selection analysis does not reveal a statistical preference between $Λ$CDM and the Kinetic model.

astro-ph.CO↗

arXiv2020

Dark D-Brane Cosmology: from background evolution to cosmological perturbations

We study the cosmological predictions of the dark D-brane model, in which dark matter resides on a D-brane moving in a higher-dimensional space. By construction, dark matter interacts only gravitationally with the standard model sector in this framework. The dark energy scalar field is associated with the position of the D-brane, and its dynamics is encoded in a Dirac-Born-Infeld action. On the other hand, dark matter is identified with matter on the D-brane, that naturally couples to dark energy \textit{via} a disformal coupling. We analyse the numerical evolution of the cosmological background, highlighting the fact that there are two regimes of interest: one, in which the coupling is positive throughout; and another, in which the coupling is negative at the present. In the latter, there is the enticing possibility of having scenarios in which the coupling is positive for a significant part of the evolution, before decreasing towards negative values. In both cases, the coupling is very small at early times, and only starts to grow during the late matter dominated era. We also derive the equations for the linear cosmological perturbations, an expression for the effective time-dependent gravitational coupling between dark matter particles and present the numerical results for the CMB anisotropy and matter power spectra. This allows for a direct comparison of the predictions for the growth of large scale structure with other disformal quintessence models.

gr-qc↗

arXiv2020

Bouncing cosmology in $f(R,\mathcal{G})$ gravity by order reduction

A bouncing universe is a viable candidate to solve the initial singularity problem. Here we consider bouncing solutions in the context of $f(R,\mathcal{G})$ gravity by using an order reduction technique which allows one to find solutions that are perturbatively close to General Relativity. This procedure also acts as a model selection approach. Indeed, several covariant gravitational actions leading to a bounce are directly selected by demanding that the Friedmann equation derived within such gravity theories coincides with the one emerging from Loop Quantum Cosmology.

gr-qc↗