Since the discovery of the first planet outside our solar system twenty 20 ago, astronomers have discovered more than 5000 such exoplanets. Together with the numbers, our understanding has grown as to how planets form, what they can look like and which factors may be relevant for the formation and maintenance of complex life. Yet, despite fascinating insights and spectacular images of faraway worlds, we continue to marvel at the view back, from space to our own planet. In 2019, a group of professional astronomers came together to remind astronomers themselves about our duty to protect this planet for human civilisation, as well as share the astronomical perspective with a wider public.

Asteroseismology has opened a window on the internal physics of thousands of stars, by relating their pulsations to their internal physics. Seismic modelling requires good models and a reliable matching of the measured frequencies to the oscillation geometries. In upper main-sequence stars, that often rotate rapidly, this matching is challenging as both the structure and the oscillations are impacted by the centrifugal and Coriolis forces.

In this talk, I will describe the models we use, the mode geometries that emerge in rapidly rotating stars, and their differences with slow rotators. I will present recent progress, based on either perturbative treatments or complete calculations of rotation : line-profile variations of rapid rotators, cluster dating through delta Scuti stars, machine-learning techniques applied to mode identification and inversion techniques. Each of these facets is part of a bigger picture that is becoming clearer every day.

Winds and outflows are ubiquitous at several scales throughout the Cosmos. They often develop a bubble structure characterized by strong shocks and turbulence where high-energy particles can be efficiently produced. I will present a model in which diffusive shock acceleration is a key process to energize particles in such astrophysical winds. I will show some model applications in the context of young massive stellar clusters, starburst galaxies and active galactic nuclei and I will discuss the associated multi-messenger implications in terms of high-energy photons, neutrinos and escaping cosmic rays.

Upcoming experiments aim to retrieve highly detailed data of the distribution of matter on the largest cosmological scales, driven by the search for physics beyond the standard models of cosmology and particle physics. For this we need to control and minimise uncertainties in the theoretical modelling which is a challenging task, especially given the non-linearity and complexity of the underlying description. In this context, some of the most limiting theoretical uncertainties are shell-crossing singularities, which are instances with large matter densities that arise when trajectories of collisionless matter intersect. In this talk I provide an overview of recent advances, on both the theoretical/analytical and numerical front, for obtaining fast and accurate shell-crossing predictions.

- CR & Oliver Hahn, Phys. Rev. D 107 (2023) 2, 023515, arXiv:2211.02053
- CR, Shohei Saga, Atsushi Taruya & Stéphane Colombi, PRD accepted, arXiv:2303.12832
- CR, Uriel Frisch & Oliver Hahn, Phys. Rev. Fluids 7 (2022) 10, 104610, arXiv:2207.12416

Today, the Cosmic Microwave Background (CMB) is one of the most powerful observable to understand cosmology.
Cosmic inflation, a speculative era of primordial accelerated expansion, is the most popular very-early-universe theory that is able to explain these observations.

I will discuss the CMB and the standard model of cosmology, before presenting the status of the CMB-anisotropies measurements and how well they are able to constrain our model.
I will then focus on the future of CMB-anisotropies measurements, introducing the next-decade experiments and their forecasted constraints on our models.

I will also discuss the simplest class of inflation phenomenology, that only needs introducing a scalar field slowly rolling on its potential.
I will show the current and future constraints on this specific type of inflation realisation, before presenting how to embed such a model in a well-defined particle-physics framework, based on arXiv:2304.04534.

Future large galaxy surveys (such as Euclid, LSST, DESI) will probe the growth of structures and the expansion history with an unprecedented precision, offering new insights on the nature of dark matter, dark energy and gravity. However, the increased quality of these data also means a significant increase in the number of nuisance parameters, making the cosmological inference a very challenging task. Indeed, conventional likelihood-based methods like Markov-Chain Monte Carlo (MCMC) become extremely time-consuming when the dimensionality of the parameter space is very high. In this talk, I discuss the first application of Marginal Neural Ration Estimation (MNRE) (a recent approach in so-called simulation-based inference) to Euclid primary observables, like cosmic shear and galaxy-clustering spectra. Using expected Euclid experimental noise, I show how it’s possible to recover the posterior distribution for the cosmological parameters using an order of magnitude fewer simulations than MCMC. If time permits, I will end by briefly discussing another powerful application of MNRE: the reconstruction of the 3D primordial matter fluctuations from which present non-linear observations formed.

Upcoming galaxy surveys will provide a wealth of cosmological information. They will map almost the entire observable universe at late times, giving us the opportunity to measure correlations on very large scales, approaching the boundaries of the observable universe. At such large scales, the interpretation of the observed power spectrum will require special care, taking into account wide-angle effects, nontrivial survey geometries, and relativistic corrections. I will show how these effects can bias possible future constraints on the amplitude of primordial non-Gaussianity if not properly considered.

---- Note the unusual day! ----
The SPT-3G receiver on the South Pole Telescope measures the cosmic microwave background with unprecedented precision. The on-going analysis of SPT-3G data is expected to yield cosmological constraints of higher precision than Planck that are independent of the satellite mission's results. With this constraining power comes the responsibility to employ a flexible, robust, and efficient data analysis pipeline.
In this talk, I present an in-progress view of a new likelihood software developed for SPT-3G data analysis. The likelihood code is written in python and can be used in conjunction with widely available analysis software (e.g. Cobaya). The software is designed to leverage the power of the JAX-library, such that when paired with a differentiable theory code (e.g. CosmoPower) it provides a fully differentiable analysis framework from cosmological parameters to the log likelihood. This pairing gives easy access to robust Fisher matrices with minimal computational cost. I highlight a range of applications that are greatly simplified in this framework and demonstrate how it can be leveraged to carry out a volume of consistency tests on the data otherwise computationally unfeasible. Finally, I provide an overview of other types of applications that are only made possible through the gradient-information, such as more efficient exploration of the likelihood surface.

Black hole magnetospheres and jets host collisionless and highly magnetized plasmas that shine across the electromagnetic spectrum. In such plasmas, collisionless magnetic reconnection is an important process, because it can liberate energy stored in the strong magnetic field, accelerating particles that then produce the observed light. To study magnetic reconnection in the collisionless regime relevant here demands a kinetic (as opposed to a fluid, e.g., magnetohydrodynamic) description, and, for this task, the particle-in-cell (PIC) computational method provides a well-suited tool. In this talk, I present two PIC simulation studies of magnetic reconnection as may occur in the jets and magnetospheres of black holes. First, I focus on jets launched by active galactic nuclei and observed head-on as blazars. Here, reconnection couples, at the highest observed photon energies, to electron-positron pair production, leading to radiative signatures reminiscent of gamma-ray flares from flat-spectrum radio quasars. In the second part of my talk, I discuss ongoing efforts to model the accretion of alternating-polarity loops of poloidal magnetic flux onto a spinning black hole. In this context, magnetic reconnection explosively tears the loops open, modifying the polarity of the nascent jet while also providing a potentially observable magnetospheric signal.