Main Colloquium
Patrick Reichherzer	SCHEDULED

University of Oxford

Galaxy clusters host a zoo of radio morphologies—from compact bubbles and extended halos to sausages, bridges, and relics—all generated by cosmic rays (CRs) interacting with magnetic fields. The transport of these CRs across galaxy clusters reflects a reciprocal interaction across plasma scales. Large-scale processes (≳kpc) typically influence microscale behavior (~npc), but we show that microscale fluctuations—inherently patchy and intermittent in nature—shape large-scale radio morphologies in galaxy clusters by mediating CR propagation. This patchiness creates a heterogeneous medium where various plasma microinstabilities collectively affect CR transport. Our multi-scale simulations (kinetic to MHD) show a scale-dependent diffusion coefficient, with a transition at ~1–10 kpc: diffusion dominates below this scale, while advection takes over above it. This interplay shapes radio morphologies, revealing that microscale physics significantly affects macroscopic CR transport. We reveal that microscale physics isn't just driven—it actively sculpts the radio sky, offering testable predictions for next-generation observations.

	Promotionskolloquium
Davit Alkhanishvili	SCHEDULED

AIfA, Bonn

The Lambda-CDM model is the standard in cosmology, with large-scale structure clustering measurements playing a key role in parameter constraints. Next-generation galaxy surveys highlight the growing importance of higher-order statistics like the bispectrum, which offers improved constraints but introduces computational challenges. This thesis focuses on modeling the bispectrum using perturbation theory to enhance its role in extracting cosmological information. First, we test next-to-leading order perturbation theory expansions using N-body simulations, finding that effective field theory (EFT) provides the most accurate small-scale predictions. We also assess the impact of systematic and statistical errors. Next, we demonstrate how deep neural networks can be employed to model survey geometry effects on the power spectrum and bispectrum, achieving high accuracy with efficient computation. Lastly, we evaluate a third-order galaxy bias expansion against synthetic Eucilid-like survey catalogues, demonstrating that combining the power spectrum and bispectrum allows accurate cosmological parameter extraction up to mildly non-linear scales, improving constraints by a factor of 2-5 over the power spectrum alone.