The physics we glean from the small-scale Universe

Boryana Hadzhiyska (Berkeley Lab)

September 11, 2023

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Abstract: With the expected increase in volume that late- and early-Universe experiments such as DESI, Euclid, Roman, ACT, SO and CMB-S4 will provide, the precision on the small-scale observables will improve dramatically. Of particular interest to stress-testing the LCDM paradigm and probing beyond it are measurements on small scales, which encode information about the behavior of neutrinos, dark matter, gravity, etc. However, a major challenge in utilizing these exquisite small-scale data is our poor understanding of astrophysical effects related to galaxy formation and baryonic feedback. These can be revealed by studying the cross-correlation between late-time structures such as galaxy clusters and the Sunyaev-Zel dovich effect imprinted on the CMB map, but the issue is that our models have not yet been fully verified through real observations. In this talk, I will give an overview of my work on using state-of-the-art simulations to inform our small-scale physics models in the context of analyzing upcoming surveys, and also on using observations to calibrate our simulation models. I will then present a few actively ongoing projects as part of the recent ACTxDESI MoU, incorporating various simulation-enhanced models (enhanced galaxy-halo models, Hybrid Effective Field Theory, Y-tau relation in kSZ reconstruction) in an effort to constrain astrophysics, the growth of structure and primordial non-Gaussianity from the joint analysis of late- and early-Universe probes. Hopefully, I will convince you that refining our small-scale models with the help of sophisticated simulation-based techniques is invaluable for increasing the astrophysical and cosmological yield from data in the next decade.