Talks

Inflaton couplings during warm inflation result in the production of a thermal bath. Thermal fluctuations can dominate the standard de Sitter analogues, resulting in a modified slow-roll scenario with a new source of density fluctuations. It is generally difficult to reliably calculate the predictions of warm inflation, and therefore assess its viability as a model of the early universe. We will present a fully calculable perturbative model of warm inflation, and discuss its main features. We will see that the thermal bath develops a chemical potential. The chemical potential has a rather large impact, and in extreme cases the chemical potential can stop warm inflation from happening all together.

Defining thermodynamic ensembles for gravitational systems is tied to specifying boundary conditions. In this talk I'll first briefly review how introducing a Dirichlet timelike boundary clarifies thermodynamics of de Sitter space. Then I'll discuss geometries subjected to conformal boundary conditions, where the conformal class of the boundary metric and the trace of the extrinsic curvature K are held fixed. In the high temperature limit the series of subextensive terms in the free energy are compared to predictions from thermal effective field theory, and we observe agreement in all considered cases. Ensembles with negative K include solutions with cosmic-type horizons, where the system boundary is smaller than the horizon. In some regions of parameter space, these solutions are the dominant phase and are necessary for consistency with thermal effective field theory.

Uncovering the origins of binary black holes through gravitational-wave detections provides a powerful probe of the evolution, interactions, and environments of massive stars. Stellar theory predicts a forbidden range of black-hole masses between 50-130Msun due to pair-instability supernovae, but evidence for such a gap in the mass distribution in previous gravitational-wave studies has proved elusive. In this talk, I will present our latest observational evidence of the pair-instability gap in the distribution of black hole masses. While the gap is not present in the distribution of primary masses (the bigger of the two black holes in a binary system), it appears unambiguously in the distribution of secondary masses. The location of the gap lines up well with a previously identified transition in the binary black-hole spin distribution; binaries with primary components in the gap tend to spin more rapidly than those below the gap. We interpret these findings as evidence for a subpopulation of hierarchical mergers: binaries where the primary component is the product of a previous black-hole merger and thus populates the gap. If time permits, I will also highlight the signatures of hierarchical mergers that not only populate the mass gap but also present at lower mass.

Multiprobe techniques are at the forefront of modern cosmological analysis. In this talk, I will demonstrate the advantages of the multiprobe approach for assessing internal consistency, mitigating systematic effects, and breaking parameter degeneracies across datasets spanning different scales and redshifts. I will showcase these benefits using a comprehensive multiprobe pipeline, developed over a series of analyses, that combines cosmic microwave background (CMB) and large-scale structure (LSS) observations, including all possible cross-correlations between probes. In the second half of the talk, I will present recent results from the pipeline demonstrating how multiprobe analysis can address fundamental questions such as the nature of dark energy and the sum of neutrino masses. Finally, I will look forward to applications with upcoming CMB and LSS surveys. I will highlight how the multiprobe pipeline, combined with modular tools I have developed for effective field theory of large-scale structure (EFTofLSS) modelling and beyond-Limber angular power spectrum computation, positions this work for natural extension to next-generation (Stage-IV) datasets.

Coherent states conveniently represent the classically meaningful wavelike states of light, as opposed to the corpuscular number states, but superposing coherent states is mind-bogglingly unclassical, including as examples "cat states", "comb states" and "compass states". I present a history of superposing coherent states, especially for oscillators (including electromagnetic field states) and for spin, and extend to entangled coherent states. I then show that superposed coherent states are a viable path for photonic quantum computing and for reaching towards the ultimate limits of sensing. Finally, I discuss our experimental realisations (at University of New South Wales) of superposed coherent states in a spin-7/2 Antimony nucleus in a silicon substrate.

Most physical theories assume that spacetime is four dimensional, a claim strongly supported by high precision accelerator and cosmological measurements. It is also well known that at the Planck scale our quantum theories, and perhaps physics itself, break down. This raises a natural question: what happens to spacetime at the smallest scales, where quantum fluctuations may alter the familiar four dimensional structure? What is the dimension of quantum spacetime? How should we understand topology in this regime, and can matter and spacetime topology be defined independently? My talk will present possible answers to these questions through the lens of Causal Dynamical Triangulations.