William Matthewson
Korea Astronomy and Space Science Institute

Abstract
I will present a discussion of some recent works, ranging from some of the latest DESI results, to preparation for Euclid. Each of these surveys will play an important role in the study of the large scale structure of the universe in the coming years. The second data release of DESI BAO put impressive constraints on cosmology, including the w0waCDM parametrization of dark energy, showing a slight preference for effective phantom behaviour at higher redshifts. Since this 2-parameter extension of LambdaCDM might be prone to bias, or insensitive to certain behaviours, it is important to test the results using more flexible, model-independent reconstructions. We find consistent trends in reconstructions from Crossing Statistics, Binning and Gaussian Processes, supporting the robustness of the Key paper result (arXiv:2503.14738). In a subsequent work, we tested a particular Braneworld model which provides a physical means for the observed behaviour in the dark energy equation of state. We show that the fit to the data obtains a similar Deltachi^2 to the w0waCDM, indicating that this model is similarly preferred over LambdaCDM, by the data. Finally, we look to the future and the planned Euclid Year 1 and Year 3 photometric results, focusing on the angular power spectrum of galaxy number counts. Approximations will become increasingly important as we perform analyses like MCMC that require the efficient calculation of many power spectra. The conventional Limber approximation approach is known to perform badly in various regimes, and we compare it to an alternative (the “flat-sky” approximation) for the particular case of Euclid. The results show that by Year 3, it will become necessary to move past the Limber approximation to something more accurate, and the flat-sky approximation might provide this alternative.

2025 December 02, 16:00

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto