Overview

I am broadly interested in developing we can use to learn about the universe. This encompasses theoretical predictions and computational simulations of different observations, analysis techniques to extract and interpret interesting signals from data, and planning for future observational campaigns. See below for a selection of specific topics I have worked on.


Line Intensity Mapping

We can make large maps of the large-scale structure of the universe by measuring fluctuations in the intensity of radiation from different atomic or molecular transitions occurring in galaxies or the intergalactic medium. This method is highly complementary to traditional galaxy surveys, involving different technology and in principle allowing access to much larger distances away from us. I am working at the forefront of this exciting new area.


The CHIME telescope

The Canadian Hydrogen Intensity Mapping Experiment is currently collecting data from its site near Penticton, BC, Canada, with the goal of measuring the imprints of primordial sound waves in the cosmic distribution of neutral hydrogen. My contributions include developing methods for foreground removal and cosmological interpretation of these measurements, and supervision of software infrastructure development.
Website


Lensing of line intensity maps

Techniques developed for measuring lensing of cosmic microwave background maps can be adapted for line intensity maps (including, but not limited to, 21cm emission from neutral hydrogen). However, one must be careful to account for the nonlinear, non-Gaussian nature of these maps.
Paper link



Cosmological Perturbation Theory

At very large distances, we have a robust theoretical description of the statistics of density fluctuations in the universe, as traced by luminous objects such as galaxies. As we examine smaller and smaller distances, this description begins to break down as clustering gets stronger. Cosmological simulations are a helpful tool for investigating this regime, but there is also a range of distances at which the deviations from the ong-distance description are small enough that they can be treated as perturbations, and systematically accounted for using perturbation theory. This is most usefully phrased using the language of effective field theory, borrowed from particle physics, and this language has allowed for a number of advances in the robustness of these predictions.


Computation of 2- and 3-point statistics

Effective field theory techniques can be used to compute clustering statistics (the so-called matter power spectrum and bispectrum) in a self-consistent and systematic way.
Paper links: 1 2 3 4 5


Precision comparison with simulations

This approach to cosmological perturbation theory yields impressive results when compared with large simulations of gravitational clustering.
Paper link





Large-scale density reconstruction

Perturbation theory describes couplings between large-scale and small-scale Fourier modes of the cosmic density field, and these couplings can be exploited to reconstruct large-scale modes from their effects on the statistics of the small-scale modes. However, the relationship between galaxy and matter clustering must be carefully accounted for.
Paper link


Baryonic Effects in Large-Scale Structure

The clustering of galaxies, and matter in general, is not only determined by gravitational forces at large distances, but is influenced by astrophysical processes such as gas cooling, star formation, and energy injection by supernovae and the surroundings of supermassive black holes. These so-called "baryonic" effects need to be understood to make the most use of clustering measurements that will be made in the near future.

Baryonic effects on CMB lensing

Upcoming measurements of gravitational lensing of the cosmic microwave background will be used for a variety of purposes, but their interpretation can be contaminated by the influence of baryons. A range for the size of this contamination can be estimated from simulations, and these simulations can also be used to develop and test several different strategies for mitigating this effect.
Paper links: 1 2


Baryonic effects on matter 3-point statistics

These effects on 3-point statistics have not been investigated as extensively as for 2-point statistics, but 3-point correlation function measurements could provide a new pathway to constraining simulation-based models for these effects, or testing the consistency of different modelling approaches.
Paper link



Baryonic effects on cosmic shear

The lensing distortions of observed galaxy shapes are affected by these effects, and this is often seen as a nuisance that obscures useful cosmological information. However, one can also use lensing to constrain models for these effects, and obtain interesting constraints even from near-term galaxy surveys.
Paper link




Cosmic Microwave Background

The CMB has been the workhorse of modern cosmology, providing unparalleled information about the overall properties of the universe. However, there is still a large amount of untapped information that future CMB surveys will measure, and even current data can be used in new, novel ways.


Cosmic strings in the CMB

Anticipated constraints on the average tension of cosmic strings will be weakened if other properties of the strings, such as their mean velocity and "wiggliness" are left free in the modeling. Predictions that explore this full parameter space can be rather computationally expensive, but an efficient code that interpolates between the results of full evaluations can greatly speed up the parameter estimation process.
Paper link


Inhomogeneous cosmology

It has been proposed that dark energy can be replaced by a large, underdense void as an explanation for the recent acceleration of the cosmic expansion. Such an explanation would lead to a large CMB dipole, unless we are located very close to the void center. Comparison with the observed CMB dipole yields a tuning problem for void models of this type.
Paper link


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