Planned efforts to probe the largest observable distance scales in future cosmological surveys are motivated by a desire to detect relic correlations left over from inflation and the possibility of constraining novel gravitational phenomena beyond general relativity (GR). On such large scales, the usual Newtonian approaches to modelling summary statistics like the power spectrum and bispectrum are insufficient, and we must consider a fully relativistic and gauge-independent treatment of observables such as galaxy number counts in order to avoid subtle biases, e.g. in the determination of the fNL parameter.In this work, we present an initial application of an analysis pipeline capable of accurately modelling and recovering relativistic spectra and correlation functions. As a proof of concept, we focus on the non-zero dipole of the redshift-space power spectrum that arises in the cross-correlation of different mass bins of dark matter haloes, using strictly gauge-independent observable quantities evaluated on the past light cone of a fully relativistic N-body simulation in a redshift bin 1.7 ≤ z ≤ 2.9. We pay particular attention to the correct estimation of power spectrum multipoles, comparing different methods of accounting for complications such as the survey geometry (window function) and evolution/bias effects on the past light cone, and discuss how our results compare with previous attempts at extracting novel GR signatures from relativistic simulations.

The standard cosmological model is inherently relativistic, and yet a wide range of cosmological observations can be predicted accurately from essentially Newtonian theory. This is not the case on ‘ultra-large’ distance scales, around the cosmic horizon size, however, where relativistic effects can no longer be neglected. In this paper, we present a novel suite of 53 fully relativistic simulations generated using the gevolution code, each covering the full sky out to z ≈ 0.85, and approximately 1930 square degrees out to z ≈ 3.55. These include a relativistic treatment of massive neutrinos, as well as the gravitational potential that can be used to exactly calculate observables on the past light cone. The simulations are divided into two sets, the first being a set of 39 simulations of the same fiducial cosmology (based on the Euclid Flagship 2 cosmology) with different realisations of the initial conditions, and the second which fixes the initial conditions, but varies each of seven cosmological parameters in turn. Taken together, these simulations allow us to perform statistical studies and calculate derivatives of any relativistic observable with respect to cosmological parameters. As an example application, we compute the cross-correlation between the Doppler magnification term in the convergence, κv, and the CDM+baryon density contrast, δcb, which arises only in a (special) relativistic treatment. We are able to accurately recover this term as predicted by relativistic perturbation theory, and study its sample variance and derivatives with respect to cosmological parameters.

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The Cosmological Principle (CP) is part of the foundation that underpins the standard model of the Universe. In the era of precision cosmology, when stress tests of the standard model are uncovering various tensions and possible anomalies, it is critical to check the viability of this principle. A key test is the consistency between the kinematic dipoles of the cosmic microwave background and of the large-scale matter distribution. Results using radio continuum and quasar samples indicate a rough agreement in the directions of the two dipoles, but a larger than expected amplitude of the matter dipole. The resulting tension with the radiation dipole has been estimated at ∼5σ for some cases, suggesting a potential new cosmological tension and a possible violation of the CP. However, the standard formalism for predicting the dipole in the two-dimensional projection of sources overlooks possible evolution effects in the luminosity function. In fact, radial information from the luminosity function is necessary for a correct projection of the three-dimensional source distribution. Using a variety of current models of the quasar luminosity function, we show that neglecting redshift evolution can significantly overestimate the relative velocity amplitude. While the models we investigate are consistent with each other and with current data, the dipole derived from these, which depends on derivatives of the luminosity function, can disagree by more than 3σ. This theoretical systematic bias needs to be resolved before robust conclusions can be made about a new cosmic tension.

Early Universe physics leaves distinct imprints on the Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS). The current cosmological paradigm to explain the origin of the structures we see in the Universe today (CMB and LSS), named Inflation, says that the Universe went through a period of accelerated expansion. Density fluctuations that eventually have grown into the temperature fluctuations of the CMB and the galaxies and other structures we see in the LSS come from the quantization of the scalar field (inflaton) which provokes the accelerated expansion. The most simple inflationary model, which contains only one slowly-rolling scalar field with canonical kinetic term in the action, produces a power-spectrum (Fourier transform of the two-point correlation function) approximately scale invariant and an almost null bispectrum (Fourier transform of the three-point correlation function). This characteristic is called Gaussianity, once random fields that follow a normal distribution have all the odd moments null. Yet, more complex inflationary models (with more scalar fields and/or non-trivial kinetic terms in the action, etc) and possible alternatives to inflation have a non-vanishing bispectrum which can be parametrized by a non-linearity parameter f NL , whose value differs from model to model. In this work we studied the basic ingredients to understand such statements and focused on the observational evidences of this parameters and how the current and upcoming galaxy surveys are able to impose constraints to the value of f NL with a better accuracy, through the multi-tracer technique, than those obtained by means of CMB measurements.

The cross-correlation between 21-cm intensity mapping experiments and photometric surveys of galaxies (or any other cosmological tracer with a broad radial kernel) is severely degraded by the loss of long-wavelength radial modes due to Galactic foreground contamination. Higher-order correlators are able to restore some of these modes due to the non-linear coupling between them and the local small-scale clustering induced by gravitational collapse. We explore the possibility of recovering information from the bispectrum between a photometric galaxy sample and an intensity mapping experiment, in the context of the clustering-redshifts technique. We demonstrate that the bispectrum is able to calibrate the redshift distribution of the photometric sample to the required accuracy of future experiments such as the Rubin Observatory, using future single-dish and interferometric 21-cm observations, in situations where the two-point function is not able to do so due to foreground contamination. We also show how this calibration is affected by the photometric redshift width σz, 0 and maximum scale kmax. We find that it is important to reach scales k ≳ 0.3 h Mpc−1, with the constraints saturating at around k ∼ 1 h Mpc−1 for next-generation experiments.

We have seen an unprecedented development in the field of cosmology, in the past decades, with the development of increasingly detailed cosmic microwave background maps. Notwithstanding, the amount of information one can extract from those two-dimensional maps is limited when compared to what can be achieved through the three-dimensional mapping obtained with galaxy surveys. The spatial dark matter distribution inferred with these surveys depends on the highly non-linear gravitational collapse, which can be incorporated in our three-dimensional description through N-body simulations (usually performed within Newtonian gravity) up to the tens of Mpc scales. In contrast, scales at the order of hundreds of Mpc are free from astrophysical effects and can be accurately described with perturbation theory. At these scales, relic features characteristic of primordial universe physics are left in the n-point statistics of dark matter tracers (e.g. galaxies and halos), and we can obtain novel gravitational effects through a theory-observables connection (the latter which are based on a set of fundamental observables such as redshift and observed angles on the sky). Primarily, we explore the relativistic anisotropies in the dark matter halo distribution that emerge after connecting the observed redshift with its theoretical general relativistic prediction. We focus on the power-spectrum dipole (2-point statistics) signal that appears after cross-correlating different halo populations (i.e. different masses) obtained from a weak-field relativistic N-body simulation. We make a complete presentation of the details necessary to extract essential parameters to model and interpret the results on an observed light cone. From an observational perspective, while it is desirable to have high-precision redshifts, we also require a large volume coverage to reach the necessary scales at which relativistic and primordial non-Gaussian effects (the latter is a characteristic feature of inflationary models) are manifested. However, when dealing with discrete dark matter tracers, we must acquire a large number of observations for the n-point signal to overcome its noise. Large volumes can be densely mapped through the so-called photometric redshifts, at the cost of redshifts with spectroscopic precision. Therefore, our second objective is to calibrate photometric redshifts utilising the clustering information of both galaxies and neutral hydrogen intensity mapping. We assess the ability of the bispectrum (3-point statistics) to recover the redshift distribution parameters, and we compare the results with the power spectrum. We also verify, for both 2-and 3-point statistics, how this clustering redshifts method depends upon the foreground contamination present in the neutral hydrogen maps.

Esforços para observar as maiores escalas do Universo com levantamentos de galáxias futuros são motivados pelo desejo de detectar correlações oriundas de um possível período inflacionário e da possibilidade de restringir fenômenos que vão além da relatividade geral. Em escalas extremamente grandes, a abordagem Newtoniana é insuficiente para modelar o espectro de potências e o bispectro. Portanto, para interpretarmos corretamente as medidas em tais escalas, devemos considerar um tratamento relativístico e independente de calibre para as observáveis cosmológicas (e.g. contagem de galáxias). Revisarei as principais características físicas das escalas ultralargas (i.e., da ordem do horizonte cosmológico), dando particular atenção para possíveis equívocos na restrição de parâmetros inflacionários e para a característica mais marcante do espectro e bispectro relativísticos: a presença de momentos ímpares na expansão de Legendre. Também mostrarei, brevemente, como é possível utilizar halos contidos em um cone de luz de uma simulação de N -corpos relativística para modelar e recuperar o dipolo relativístico.Palavras-chave estrutura em larga escala do universo, efeitos relativísticos, inflação cósmica IntroduçãoA cosmologia é uma ciência recente, incorporando-se ao repertório científico, ao longo do século 20, com o estabelecimento da relatividade geral e com a emergência de uma comunidade científica interessada em estudos sobre a origem, constituição e evolução do universo. Hoje, somos capazes determinar parâmetros cosmológicos do modelo convencional da cosmologia, também conhecido por ⇤CDM, com alta precisão. Esse modelo adota a relatividade geral como a teoria que explica como a matéria interage e colapsa gravitacionalmente, utilizando-se do princípio cosmológico (homogeneidade e isotropia espacial) para a estatística da distribuição dos campos cosmológicos (campo gravitacional, distribuição de matéria, etc) para adotar a métrica de Friedman-Lemaître-Roberton-Walker (FLRW) e resolver as equações de Einstein, extrapolando leis físicas locais para escalas cosmológicas.A nível de um universo homogêneo e isotrópico, ou seja, sem perturbações em torno da média global, soluções das equações de Einstein implicam que, em momentos mais primitivos do universo, radiação na forma de fótons era a componente dominante, seguido por um período dominado por matéria e, finalmente, no predomínio tardio de um fluido de energia escura dominando a dinâmica do sistema. Note que isso acontece ao assumirmos a presença específica de tais componentes. Vínculos atuais nos mostram que, para esse modelo, o universo é composto, atualmente, por 31% de matéria, que engloba a matéria escura fria (CDM) e bárions, e 69% de energia escura descrita por uma constante cosmológica ⇤ 1 . Em termos dos parâmetros de densidade ⌦ X,0 : ⌦ m,0 = ⌦ CDM,0 + ⌦ barions,0 = 0.31 e ⌦ ⇤,0 = 0.69, onde o índice 0 refere-se a essas quantidades hoje.Contudo, um universo perfeitamente homogêneo e isotrópico não resulta no universo observado, dado que as densidades ⇢ de matéri...