As our advanced telescopes produce ever larger and deeper maps of our Universe we need to consider that observations are taken on our past light cone and on a spacetime geometry that is pervaded by small distortions. A precise understanding of the weak-field regime of General Relativity allows one to model these aspects consistently within N-body simulations of cosmic structure formation. The...
Our current perturbation theory techniques for predicting the power spectrum break down when we enter the non-linear regime (k~0.1 h/Mpc). Simulations allow us to probe this regime, however one must be run for every cosmology and gravity model one wishes to constrain. A perturbation theory technique that could push further into the non-linear scales than current methods and match the accuracy...
Cosmic voids gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint on degree scales. We aimed to probe the consistency of simulated ΛCDM estimates and observed imprints of voids identified in the first year data set of the Dark Energy Survey (DES Y1) by cross correlating with CMB . In particular, we intended to explore other aspects of the...
Large scale structure simulations are a fundamental tool to interpret data from large volume galaxy surveys. In fact, modelling the observables and their covariance is affected by the non-linear regime of gravitational collapse, a phenomenon that is best captured through simulations. In this talk I will present some applications of simulations that are relevant to present and upcoming galaxy...
The large-scale structure of the universe is mostly the consequence of the gravitational clustering of cold dark matter (CDM). Eventually the CDM trajectories begin to intersect ("shell-crossing"), which marks the starting point of elaborate computations in the phase-space. I show that, due to the collisionless nature of CDM, phase-space trajectories exhibit weakly singular behaviour such as...
The Kilo-Degree Survey is providing a weak gravitational lensing tomography map of the large-scale structure back to redshift ~1. We recently completed observations. First results, based on 1/3 of the final data set, indicate that the large-scale structure is slightly smoother than predicted in the best-fit Planck 2018 cosmology. I will discuss the methodology that led to this result, in...
We present a realistic Markov-Chain Monte-Carlo (MCMC) forecast for the precision of neutrino mass and cosmological parameter measurements with a Euclid-like galaxy clustering survey. We use the most general perturbation theory model for the one-loop power galaxy spectrum and tree-level bispectrum. This model is based on cosmological perturbation theory and includes non-linear bias, redshhift...
The statistical analysis of lensed galaxies is a powerful tool to study the dark matter distribution of the Universe. For instance, the distortion of galaxy shapes induced by the large scale structure of the Universe can be used to reconstruct the projected matter density along the line-of-sight (mass maps). Mass maps are useful as they provide a wealth of information that goes beyond and...
The large scale structure bispectrum in the squeezed limit couples large with small scales. Since relativity is important at large scales and non-linear loop corrections are important at small scales, the proper calculation of the observed bispectrum in this limit requires a non-linear relativistic calculation. We compute the matter bispectrum in general relativity in the weak field...
We develop a cosmological parameter estimation code for (tomographic) angular power spectra analyses of galaxy number counts, for which we include, for the first time, redshift-space distortions (RSD) in the Limber approximation. This allows for a speed-up in computation time, and we emphasise that only angular scales where the Limber approximation is valid are included in our analysis. Our...
In this talk I will present new cosmic shear results based on the combined KiDS optical and VIKING infrared data over an area of 450 square degrees. I will show how the crucial redshift calibration benefits from the extended wavelength coverage and how this leads to more robust cosmological conclusions. The results will be put into context and compared to findings from the two other big cosmic...
We present an iterative method to reconstruct the linear-theory initial conditions from the late-time cosmological matter density field, with the intent of improving the recovery of the cosmic distance scale from the baryon acoustic oscillations (BAOs) and making the distance measurements more reliable in upcoming redshift surveys, e.g., PFS, DESI and Euclid. We apply the iterative method to...
We revisit the clustering of relic neutrinos in the gravitational potential of the Milky Way. Previous work was based on forward-tracking of particles from high redshift. As the orbits of the neutrinos depend quite sensitively on their initial conditions, determining their density at a particular position, e.g. the sun, is however computationally inefficient. Consequently, the equations of...
My talk has two parts. First, I talk about second-order lensing of 21cm intensity mapping (IM). Like the CMB, 21cm IM temperature fluctuations have second and higher order lensing and no first-order lensing. We find a new (third order) lensing term that is neglected in the CMB lensing but is important for 21cm IM. We study the detectability of 21cm IM lensing with a Fisher matrix approach for...
In the next decade we will almost certainly measure the neutrino mass sum to high significance. Neutrino cosmology faces a revolution due to upcoming large-scale structure surveys such as Euclid and DESI. Although accurate modelling of non-linear scales will be crucial for reaching high levels of significance, we will have a wealth of data from other sources as well: future CMB experiments...
