Conference

Compact, spinning, and horizonless spacetimes can develop an ergoregion, where massless negative-energy states are quasi-trapped and drive the ergoregion instability. I will briefly review the linear mechanism and then describe recent progress in understanding the nonlinear evolution. Nonlinear mode coupling can amplify high-frequency modes through a turbulent direct cascade inside the ergoregion. Gravitational backreaction leads to an enhancement of the unstable process, and ultimately, black hole formation. I will illustrate the relevant dynamics and discuss implications for strongly gravitating horizonless systems.

The Perimeter Institute has provided me with 16 years of interactions, engagement and stimulating discussion. I'll describe some of my happy times at Perimeter and focus on one research area of interest: ultralight axions as a cosmological component. I'll describe constraints from the cosmic microwave background and large scale clustering of matter, through to novel constraints from voids and future prospects from stellar streams.

In this talk I will discuss one of the frontiers of both theory and data analysis in gravitational wave astronomy - understanding the ringing of black holes and probing them from real data. I will review past efforts started from Chandrasekhar, Detweiler, et al in analyzing modes of black holes and explain what we currently understand in both linear and nonlinear wave properties, as well as the corresponding detection aspect. At last I will show a few pressing problems and where we will be heading.

I will discuss BBN and a new python-based tool (PRyMordial) which allows one to easily simulate it both in the context of a standard cosmological model as well as in various scenarios of physics beyond the Standard Model. I’ll discuss how BBN provides a unique probe of physics relevant for the ~ MeV scale, and how it constrains or hints at modifications to the standard picture.

A number of theories predict heavy dark matter, including WIMPs and high mass composite states formed in the early universe. Discovering the heaviest dark matter candidates, with a unit mass in excess of a microgram, requires methods beyond traditional underground experiments. For high mass dark matter searches in general (including WIMPS) new search methods will be necessary in the coming decades. I will discuss the most trenchant past searches for high mass dark matter along with future prospects.

Dark matter (DM) remains one of the most enduring mysteries in fundamental physics, motivating a wide array of theoretical models and experimental searches. Axions and axion-like particles (ALPs) are theoretically well-motivated, as they naturally arise from theories with broken global symmetries. These particles may serve as viable DM candidates themselves or act as mediators between DM and the Standard Model. In this talk, I will present an overview of axion and axion-mediated DM models, including both classic QCD axions and broader classes of ALPs. Emphasis will be placed on novel mechanisms shaping the cosmic DM abundance, and on innovative strategies for detecting these elusive particles. I will highlight how forthcoming laboratory efforts, such as fixed-target and direct detection experiments, alongside astrophysical observations, are poised to explore uncharted regions of parameter space and deepen our understanding of the connections between axion physics and dark matter.

In this talk, I will give an overview of why the PN formalism is still relevant to model gravitational waves, focusing on recent synergies with other techniques and research topics. Taking the example of EFT-inspired higher curvature gravity theories, I will present a way towards building better gravitational wave tests to be used by next generation detectors.

How did the universe evolve prior to the creation of the cosmic microwave background? There are no direct observational probes of the universe’s expansion history prior to the onset of Big Bang nucleosynthesis (BBN), and numerous theories predict deviations from radiation domination during the universe’s first second. Meanwhile, a persistent discrepancy between local and cosmological measurements of the Hubble constant has prompted us to reconsider the evolution of the universe between BBN and recombination. Since the growth of dark matter density perturbations depends on the expansion rate, deviations from the standard expansion history leave imprints on the matter power spectrum. I will discuss how adding decaying massive particles or fast-rolling scalar fields to the standard cosmological model impacts the abundance and structure of dark matter halos. Both cases illustrate how small-scale structure provides a powerful probe of the evolution of the universe prior to recombinatio