Restrictions in the dark sector of the universe and modified gravity with large scale structure and gravitational waves

[EN]The current paradigm of Cosmology is founded on the ⇤ Cold Dark Matter (⇤CDM) prescription, thanks to the enormous amount of experiments in agreement with it. The building process of the ⇤CDM paradigm has three pillars, namely: General Relativity, the Cosmological Principle and the presence of a puzzling Dark Sector. However, ⇤CDM model is not able to answer all questions. For example, about the intrinsic nature of the Dark Sector, certain issues on the formation of structures in the Universe and current tensions between datasets. Consequently, the last word has yet to be spoken regarding the description of the Cosmos. Because of that, this PhD dissertation intends to be a step forward in the improvement of our cosmological knowledge. After two chapters devoted to the current concordance model and its main problems respectively, as an introduction, the main topic of this PhD thesis is presented in the third chapter: the so-called pure momentum transfer models. They are an alternative description of the Cosmos which add to the concordance scenario the presence of a momentum exchange between certain components of the Universe involving the Dark Sector. That kind of interactions preserve the background cosmology while modifying the perturbation regime, where precisely certain tensions have emerged in recent times. Moreover, we can also understand them as the macroscopic description of a microscopic force acting in the Dark Sector due to a yet invisible charge. The main implication of this pure momentum exchange is the freezing of the density perturbations of the pressureless fluid, leading to a late-time mechanism eraser of structure. In this thesis, we first present three different momentum transfer models to subsequently thoroughly study, both analytically and numerically, their background cosmology and their linear perturbation regime. We then explore all the different effects on several observables to later use the most recent data to constrain the model parameters along with the cosmological parameters. After that, we devote a chapter to the analyses of how future planned surveys will be capable or not of disentangling the presence of the pure momentum transfer interactions. In the final chapter, we focus on the very small scales where the non-linear physics takes place, as the next natural step once the background and linear cosmology has been studied along with the performance of future surveys. We analyse how these models affect the formation of structures in our Cosmos, using the first one presented before as a proxy. Finally, we summarise the work done and we present our conclusions together with the possible future prospects and open questions. [ES]El paradigma actual de la Cosmología es el modelo de Constante Cosmológica con Materia Oscura Fría, llamado modelo ⇤CDM, debido a la gran cantidad de experimentos que así lo confirman. Dicho paradigma cosmológico está basado en tres pilares: Relatividad General, el Principio Cosmológico y un enigmático Sector Oscuro. Sin embargo, el modelo ⇤CDM no es capaz de resolver satisfactoriamente todas las cuestiones que se le plantean, como puede ser la naturaleza intrínseca de dicho Sector Oscuro, diferentes problemas en las formación de las estructuras del Universo o las recientes inconsistencias entre diferentes experimentos. De tal forma que aún queda camino por recorrer para poder hallar una descripción plenamente satisfactoria para nuestro Cosmos, siendo este el objetivo de esta tesis doctoral. Comenzaremos dedicando dos capítulos a explicar el modelo de concordancia ⇤CDM y sus principales problemas, sirviéndonos pues de introducción, para luego presentar el principal tema de esta tesis doctoral: los modelos de transferencia de momento. Se tratan de descripciones alternativas al ⇤CDM para nuestro Universo que agregan a la descripción actual la posible presencia de un cierto intercambio de momento entre distintos componentes del Universo, especialmente de aquellos pertenecientes a su Sector Oscuro. Tienen la peculiaridad de preservar la cosmología de fondo y por tanto sólo actuar a nivel de las perturbaciones, donde precisamente han surgido discrepancias últimamente entre distintos experimentos. La anterior interacción puede ser entendida como el resultado macroscópico de una fuerza aún por descubrir actuando dentro del Sector Oscuro y causada por una carga oscura que nuestros detectores no han podido desentrañar debido a su propia naturaleza. A nivel de consecuencias, dichas interacciones se manifiestan como una reducción en el proceso de acreción de materia en las distintas estructuras del Universo que es eficiente en los estadios más tardíos del Universo. En esta tesis doctoral, primero presentamos tres modelos diferentes donde se da tal transferencia de momento para luego estudiarlos detalladamente tanto de forma analítica como de forma numérica. Se analizará su cosmología de fondo y el régimen lineal de perturbaciones para luego determinar sus posibles efectos en diferentes observables y, para finalizar, confrontarlos a los datos más recientes disponibles con el fin de constreñir sus parámetros. En el siguiente capítulo, analizaremos como los futuros experimentos serán capaces o no de detectar las interacciones estudiadas. Finalmente, en el último capítulo, estudiaremos como es el régimen no lineal de dichos modelos viendo como pueden cambiar el proceso de formación de estructuras en el Cosmos. Para acabar y así cerrar, presentaremos nuestras conclusiones sobre el trabajo aquí realizado y comentaremos sobre cuestiones futuras a continuar

Momentum transfer in the dark sector and lensing convergence in upcoming galaxy surveys

We investigated a cosmological model that allows a momentum transfer between dark matter and dark energy. The interaction in the dark sector mainly affects the behaviour of perturbations on small scales while the background evolution matches the $w$CDM solution. As a result of the momentum transfer, these kinds of models help alleviating the $\sigma_8$ discrepancy in the standard model, but do not resolve the so-called $H_0$ tension. We confirm that this is indeed the case by computing cosmological constraints. While our analysis tends to favour $\sigma_8$ values lower than in $\Lambda$CDM, we do not find evidence for a non-vanishing momentum transfer in the dark sector. Since upcoming galaxy surveys will deliver information on scales and red-shift relevant for testing models allowing momentum transfer in the dark sector, we also carried out forecasts using different survey configurations. We assessed the relevance of neglecting lensing convergence $\kappa$ when modelling the angular power spectrum of number counts fluctuations $C_\ell^{\rm ij}(z,z')$. We found that not including $\kappa$ in analyses leads to biased constraints ($\approx 1-5\,\sigma$) of cosmological parameters even when including information from other experiments. Incorrectly modelling $C_\ell^{\rm ij}(z,z')$ might lead to spurious detection of neutrino masses and exacerbate discrepancies in $H_0$ and $\sigma_8$.Comment: 26 pages, 8 figures, 8 tables. Comments welcome Updated versio

Some disquisitions on cosmological 2-form dualities

In this work we study different aspect of self-interacting 2-form fields with special emphasis in their cosmological applications. We provide the explicit construction of how massless 2-forms are compatible with the cosmological principle without resorting to the dual scalar field formulation. In terms of the 2-form, the residual Euclidean group is non-trivially realised by means of a combination of external spatial translations and internal gauge transformations. After presenting the general discussion of the dualities in cosmological scenarios, we analyse particular examples for some singular models and discuss in some detail the dual descriptions of the DBI, the cuscuton and the ghost condensate as well as the role of the duality in the effective field theories of cosmological perturbations. We then proceed to analysing scenarios with several self-interacting massless 2-forms and we show that they naturally provide the dual description of a solid. We then show how the perfect fluid and superfluids can be obtained by taking the appropriate limits in the dual formulations. We finally consider the case of massive 2-forms and their duals and briefly discuss their potential signatures in gravitational waves astronomy.Comment: 48 page

On cosmological signatures of baryons-dark energy elastic couplings

Preprint publicado en repositorio ArxiV (última revisión, V2)[EN] We consider a scenario where dark energy and baryons are dynamically coupled without any energy transfer. In this scenario, the background cosmology is unaffected and, at the perturbations level, the coupling only appears through the corresponding Euler equations of dark energy and baryons. We then explore some phenomenological consequences of this scenario and their signatures in several cosmological observables. In particular, we show its ability to suppress the growth of cosmic structures. We also constrain the parameters of the model with cosmological data and show that an interaction of dark energy with baryons on cosmological scales is mildly favoured.S

Probing elastic interactions in the dark sector and the role of S8

Preprint publicado en repositorio ArXiv (V1). El artículo se publicó posteriormente en Physical Review D., 104, 103503, 9 Nov. 2021[EN] We place observational constraints on two models within a class of scenarios featuring an elastic interaction between dark energy and dark matter that only produces momentum exchange up to first order in cosmological perturbations. The first one corresponds to a perfect-fluid model of the dark components with an explicit interacting Lagrangian, where dark energy acts as a dark radiation at early times and behaves as a cosmological constant at late times. The second one is a dynamical dark energy model with a dark radiation component, where the momentum exchange covariantly modifies the conservation equations in the dark sector. Using cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and supernovae type Ia (SnIa) data, we show that the Hubble tension can be alleviated due to the additional radiation, while the ��8 tension present in the Λ-cold-dark-matter model can be eased by the weaker galaxy clustering that occurs in these interacting models. Furthermore, we show that, while CMB+BAO+SnIa data put only upper bounds on the coupling strength, adding low-redshift data in the form of a constraint on the parameter ��8 strongly favors nonvanishing values of the interaction parameters. Our findings are in line with other results in the literature that could signal a universal trend of the momentum exchange among the dark sector.SIAgencia Estatal de InvestigaciónJunta de Castilla y Leó

Velocity-dependent interacting dark energy and dark matter with a Lagrangian description of perfect fluids

Preprint publicado en repositorio ArXiv (última revisión, V2)[EN] We consider a cosmological scenario where the dark sector is described by two perfect fluids that interact through a velocity-dependent coupling. This coupling gives rise to an interaction in the dark sector driven by the relative velocity of the components, thus making the background evolution oblivious to the interaction and only the perturbed Euler equations are affected at first order. We obtain the equations governing this system with the Schutz-Sorkin Lagrangian formulation for perfect fluids and derive the corresponding stability conditions to avoid ghosts and Laplacian instabilities. As a particular example, we study a model where dark energy behaves as a radiation fluid at high redshift while it effectively becomes a cosmological constant in the late Universe. Within this scenario, we show that the interaction of both dark components leads to a suppression of the dark matter clustering at late times. We also argue the possibility that this suppression of clustering together with the additional dark radiation at early times can simultaneously alleviate the σ8 and H0 tensions.S

J-PAS: Forecasts for dark matter - dark energy elastic couplings

We consider a cosmological model where dark matter and dark energy feature a coupling that only affects their momentum transfer in the corresponding Euler equations. We perform a fit to cosmological observables and confirm previous findings within these scenarios that favour the presence of a coupling at more than $3\sigma$. This improvement is driven by the Sunyaev-Zeldovich data. We subsequently perform a forecast for future J-PAS data and find that clustering measurements will permit to clearly discern the presence of an interaction within a few percent level with the uncoupled case at more than $10\sigma$ when the complete survey, covering $8500$ sq. deg., is considered. We found that the inclusion of weak lensing measurements will not help to further constrain the coupling parameter. For completeness, we compare to forecasts for DESI and Euclid, which provide similar discriminating power.Comment: 34 pages, 17 figures, added some clarifications and discussions, matches published versio

J-PAS: forecasts for dark matter-dark energy elastic couplings

Preprint publicado en repositorio ArXiv (última versión, V2). Publicado posteriormente en Journal of Cosmology and Astroparticle Physics, 9 julio, 2021[EN] We consider a cosmological model where dark matter and dark energy feature a coupling that only affects their momentum transfer in the corresponding Euler equations. We perform a fit to cosmological observables and confirm previous findings within these scenarios that favour the presence of a coupling at more than 3σ. This improvement is mainly driven by cluster counts from Planck Sunyaev-Zeldovich data that we include as a certain prior. We subsequently perform a forecast for future J-PAS data and find that clustering measurements will permit to clearly discern the presence of an interaction within a few percent level with the uncoupled case at more than 10σ when the complete survey, covering 8500 sq. deg., is considered. We found that the inclusion of weak lensing measurements will not help to further constrain the coupling parameter. For completeness, we compare to forecasts for DESI and Euclid, which provide similar discriminating power.S