Research

I am interested in testing and constraining extensions to the standard cosmological model, especially cosmologically-motivated modifications to General Relativity. I focus on doing this with observables which are sensitive to the growth of large-scale structure, in particular weak gravitational lensing and galaxy clustering, but also the cosmic microwave background and redshift-space distortions.

I also work on weak gravitational lensing and galaxy clustering more generally, including improved methods for modelling, mitigating, and exploiting astrophysical modelling uncertainties such as the intrinsic alignment of galaxies and galaxy bias.

In general, I am excited by any project which involves unpacking standard assumptions in cosmological analyses to ensure that our findings are as robust as possible. Some examples of my work in this vein include better modelling of intrinsic alignment contamination to weak lensing signals, understanding theoretical uncertainties, investigating parameter degeneracies, comprehensive and conservative forecasting for precision cosmology, and building a library for performing theoretical calculations of cosmological observables with documented numerical validation.

I am a member of the Rubin Observatory's Legacy Survey of Space and Time Dark Energy Science Collaboration (LSST DESC).

Software

I am team leader of the development team for the Core Cosmology Library (CCL) of LSST DESC. CCL aims to provide theoretical predictions of cosmological observables required for building the software pipelines which will analyse LSST data for dark energy science. The code is written in C with a python wrapper and is developed with the guiding principle of consistent and ongoing validation of outputs to documented numerical accuracy.

CCL is public software. Releases and the current development version can be found on github.

Publications

  • A. Chen et al., including C. D. Leonard, Constraints on dark matter to dark radiation conversion in the late universe with DES-Y1 and external data. Phys. Rev. D, Volume 103, Issue 12. June 2021. arxiv:2011.04606.

  • J. Muir et al., including C. D. Leonard, DES Y1 results: Splitting growth and geometry to test ΛCDM. Phys. Rev. D, Volume 103, Issue 2. January 2021. arxiv:2010.05924.

  • S. Samuroff et al., including C. D. Leonard, Dark Energy Survey Year 1 results: Constraints on intrinsic alignments and their colour dependence from galaxy clustering and weak lensing. Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 4. November 2019. arxiv:1811.06989.

  • T. M. C. Abbott et al., including C. D. Leonard, Dark Energy Survey Year 1 results: Constraints on extended cosmological models from galaxy clustering and weak lensing. Phys. Rev. D, 99, 123505. June 2019. arxiv:1810.02499.

  • N. E. Chisari, D. Alonso, E. Krause, C. D. Leonard et al. (The LSST Dark Energy Science Collaboration), Core Cosmology Library: Precision Cosmological Predictions for LSST. The Astrophysical Journal Supplement Series, Volume 242, Number 1. May 2019. arxiv:1812.05995.

  • A. Amon, C. Heymans, C. Blake, C. D. Leonard et al., KiDS+2dFLenS+GAMA: Testing the cosmological model with the EG statistic. Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 3. September 2018. arxiv:1711.10999.

  • C. D. Leonard , R. Mandelbaum (The LSST Dark Energy Science Collaboration), Measuring the scale dependence of intrinsic alignments using multiple shear estimates. Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 1. September 2018. arxiv:1802.08263.

  • C. D. Leonard , P. Bull, R. Allison, Spatial curvature endgame: Reaching the limit of curvature determination. Phys. Rev. D, 94, 023502. July 2016. arxiv:1604.01410.

  • C. D. Leonard , P. G. Ferreira, Catherine Heymans, Testing gravity with EG: mapping theory onto observations. Journal of Cosmology and Astroparticle Physics, 12, 051. December 2015. arxiv:1510.04287.

  • C. D. Leonard , T. Baker, P. G. Ferreira, Exploring degeneracies in modified gravity with weak lensing. Phys. Rev. D, 91, 083504. April 2015. arxiv:1501.03509.

  • T. Baker, P. G. Ferreira, C. D. Leonard, M. Motta, New gravitational scales in cosmological surveys. Phys. Rev. D, 90, 124030. December 2014. arxiv:1409.8284.

  • S. Stotyn, C. D. Leonard, M. Oltean, L. Henderson, R.B. Mann, Numerical boson stars with a single Killing vector I: The D≥5 case. Phys. Rev. D, 89, 044017. February 2014. arxiv:1307.8159.

  • N. Deppe, C. D. Leonard, T. Taves, G. Kunstatter, R. B. Mann, Critical collapse in Einstein-Gauss-Bonnet gravity in five and six dimensions. Phys. Rev. D, 86, 104011. October 2012. arxiv:1208.5250.

  • T. Taves, C. D. Leonard, G. Kunstatter, R. B. Mann, Hamiltonian formulation of scalar field collapse in Einstein-Gauss-Bonnet gravity. Classical and Quantum Gravity, 29, 1. October 2011. arxiv:1110.1154.

  • C. D. Leonard, J. Ziprick, G. Kunstatter, R. B. Mann, Gravitational collapse of K-essence matter in Painlevé-Gullstrand coordinates. Journal of High Energy Physics, 2011, 28. September 2011. arxiv:1106.2054.