Triangle Seminars

Abstract:
Cosmology is undergoing a data revolution. Surveys such as the imminent Legacy Survey of Space and Time (LSST) to be conducted by the Vera C. Rubin Observatory will deliver huge galaxy catalogues that provide critical tools for understanding the nature of dark matter and dark energy. However, in order to obtain accurate cosmological constraints from these enormous datasets, we need reliable ways of estimating galaxy properties using only photometry. I will present pop-cosmos: a forward modelling framework for photometric galaxy survey data, where galaxies are modelled as draws from a population prior distribution over redshift, mass, dust properties, metallicity, and star formation history. These properties are mapped to photometry using an emulator for stellar population synthesis, followed by the application of a learned model for a survey’s noise properties. Application of selection cuts enables the generation of mock galaxy catalogues. This enables us to use simulation-based inference to solve the inverse problem of calibrating the population-level prior on a deep multiwavelength catalogue, COSMOS2020. We use a diffusion model as a flexible population-level prior, and optimise its parameters by minimising the Wasserstein distance between forward-simulated photometry and the real COSMOS2020 survey data. The resulting model can then be used to derive accurate redshift distributions for upcoming photometric surveys, to facilitate weak lensing and clustering science. I will show applications of this framework, demonstrating how we are able to extract redshift distributions, and make inferences about galaxy evolution. I will also discuss the use of pop-cosmos as a prior for performing inference on individual galaxies in a highly scaleable manner, as well as results from analysing the Kilo-Degree Survey (KiDS) in preparation for LSST.

Abstract:
In this talk I will discuss recent progress in uncovering the presence of quantum group symmetries in both 2d and 3d gravity models. This structure is then utilized to better understand various aspects of gravitational models, such as the isometry structure within boundary correlation functions, and edge states at the black hole horizon. Largely based on 2507.13873 and 2505.00501.

Abstract:
TBA

Abstract:
Warm inflation modifies the standard supercooled picture of inflation by allowing the inflaton to interact continuously with other degrees of freedom during accelerated expansion. These interactions can ultimately sustain a radiation bath that is close to thermal equilibrium. The inflaton sector is naturally viewed as an open quantum system from this perspective, with dissipation and stochastic noise arising as effective descriptions of coupling the inflaton to environmental fields. The first part of the talk will introduce the basic physical picture of warm inflation with primordial density perturbations of classical thermal origin. 

As an example of how warm-inflationary physics links to observable signatures, I will then discuss an application to primordial cosmic magnetic fields. Magnetic fields are ubiquitously observed across astrophysical and cosmological scales, yet standard inflationary predictions fall dramatically short from current observations. The origin of this discrepancy lies in the conformal invariance of classical electromagnetism in an FLRW universe, which freezes the magnetic flux in the high conductivity limit. Conventional approaches introduce non-minimal couplings to break this symmetry but are tightly constrained and often lead to strong-coupling or backreaction issues. This obstruction is formalised in the Green–Kobayashi no-go theorem, which assumes a Bunch–Davies vacuum initial state. Embedding the gauge field in a thermal state, however, changes the problem: finite-temperature effects effectively lift the conformal constraint and provide a significant thermodynamic boost to magnetic-field amplitudes.