Astrophysics

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

In slow-roll inflationary models, the inflaton can undergo excursions on the order of the Planck scale, leading to significant changes in the properties of fields coupled to the inflaton, referred to as spectator fields. These changes may result in transitions between weakly and strongly interacting regimes, or even alterations in mass squared within the spectator field sector during inflation. Such dynamics can induce phase transitions, which have profound implications for the early Universe. In this talk, I will explore the phenomenological consequences of these phase transitions, focusing on the production of gravitational waves, curvature perturbations, non-Gaussianities, dark matter, and baryon number. I will also demonstrate how gravitational waves generated by scalar perturbations induced by phase transitions may potentially explain the alleged gravitational wave signals observed in recent pulsar timing array studies.

Cosmological observations provide strong motivation for new physics beyond the Standard Model (SM). In addition to dark energy, and dark matter, the measured density of ordinary matter presents a further challenge to the SM. Creating enough baryons in the early universe to match what is seen today is difficult, and the SM does not appear to be able to do so. In this talk I will present some of the most promising mechanisms for baryogenesis and discuss how they will be tested by planned and proposed future experiments.