Research interests

I am interested in applying and developing statistical methods to perform parameter inference and model comparison for real-world systems. Most of my research focuses on applications within the realm of observational cosmology, in particular with data which are sensitive to the growth of large-scale structure (weak gravitational lensing and galaxy clustering). I create approximate modelling tools to accelerate and enable inference, as well as data analysis techniques to ensure accurate results when applying approximate models (e.g. physics-informed dimensionality reduction). I investigate and characterise the impact of model misspecifcations in the nuisance parameter space of cosmological observables, and develop probabilistic models to capture the spatial statistics of cosmological density fields.

I am a Full Member and Builder of the Rubin Observatory's Legacy Survey of Space and Time Dark Energy Science Collaboration (LSST DESC), and previously led the LSST DESC Modelling and Combined Probes Working Group (2022-2024). Additionally, I was the lead of the development team for the LSST DESC Core Cosmology Library (CCL). CCL is a public python package which provides numerical modelling for cosmological observables, making it a key component of the LSST DESC Bayesian statistical data analysis pipeline. It is also a standalone package for numerical modelling of cosmological observables, with a user base conservatively estimated at 2500 scientists wordwide. The code is written in C with a python wrapper. It is developed in the open, and with the guiding principle of consistent and ongoing validation of outputs to documented numerical accuracy. Releases and the current development version can be found on github.

Publications

  • C MacMahon-Gellér, C. D. Leonard, P. Bull, and M. M. Rau, Meta-learning for cosmological emulation: Rapid adaptation to new lensing kernels. Submitted to RAS Techniques and Instruments. 2025. arxiv:2504.00552.

  • C. M. A. Zanoletti and C. D. Leonard, Principal Components for Model-Agnostic Modified Gravity with 3x2pt.. Submitted to Phys. Rev. D. 2025. arxiv:2503.20951.

  • N. Sarcevic, C. D. Leonard, and M. M. Rau (The LSST Dark Energy Science Collaboration). Joint Modelling of Astrophysical Systematics for Cosmology with LSST Cosmic Shear. Monthly Notices of the Royal Astronomical Society, 527 (2). 2025. arxiv:2503.20951.

  • C. MacMahon-Geller and C. D. Leonard, Intrinsic alignment from multiple shear estimates: A first application to data and forecasts for Stage IV. Monthly Notices of the Royal Astronomical Society, 528 (2). 2024. arxiv:2306.11428.

  • C. M. A. Zanoletti, B. R. Hull, C. D. Leonard, and R. B. Mann, Cosmological constraints on 4-dimensional Einstein-Gauss-Bonnet gravity. Journal of Cosmology and Astroparticle Physics, 2024(01), 043. 2024. arxiv:2310.19871.

  • C. D. Leonard, M. M. Rau, and R. Mandelbaum, Photometric redshifts and intrinsic alignments: degeneracies and biases in 3x2pt analysis.. Phys. Rev. D, 109(8), 083528. 2024. arxiv:2401.06060.

  • N. Van Alfen, D. Campbell, J. Blazke, C. D. Leonard , F. Lanusse, A. Hearin and R. Mandelbaum (The LSST Dark Energy Science Collaboration), An empirical model for intrinsic alignments: Insights from cosmological simulations.. The Open Journal of Astrophysics, 7 (2024). 2024. arxiv:2311.07374.

  • A. Paopsiamsap, N. Porqueres, D. Alonso, J. Harnois-Deraps, and C. D. Leonard , Accuracy requirements on intrinsic alignments for stage-IV cosmic shear.. The Open Journal of Astrophysics, 7 (2024). 2024. arxiv:2311.16812.

  • T. M. C. Abbott et al., including C. D. Leonard, Dark Energy Survey Year 3 Results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering. Phys. Rev. D, 107 (8), 083504. 2023. arxiv:2207.05766.

  • C. D. Leonard et al. (The LSST Dark Energy Science Collaboration), The N5K Challenge: Non-Limber Integration for LSST Cosmology. The Open Journal of Astrophysics, 6 (2023). 2023. arxiv:2212.04291.

  • 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.