Staff Members

Matt Becker

Matt’s work focuses on multidisciplinary problems related to cosmology, numerical computing, data analysis, statistics, and machine learning. He has worked on a broad range of topics from image analysis for the Dark Energy Survey to the development of multiple-plane ray tracing algorithms for computing weak gravitational lensing signals from N-body simulations. After spending several years in industry working in data science, his interests now include the application of deep generative modeling techniques to problems in computational cosmology and the use of cosmological simulations as tools for statistical inference.

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Amy Bender

Amy is an experimental cosmologist who builds instruments to measure the cosmic microwave background (CMB) and explore the evolution of the universe. Her primary focus for the past several years has been on developing the multiplexing readout systems used to operate the superconducting detectors used in CMB receivers. These complex readout systems allow many detectors to be operated using a single pair of wires. Thousands of such detectors can then be successfully cooled to sub-Kelvin temperatures where they have exceptional sensitivity to incoming light. She played a leading role in the development of the frequency-domain multiplexed readout for the SPT-3G instrument that is now successfully observing on the South Pole Telescope. Additional areas of expertise and interest include developing millimeter-wavelength detectors and the cryogenic chambers they operated in as well as techniques for analyzing the resulting data.

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Lindsey Bleem

Does the accelerating expansion of the universe require a modification to our theories of gravity or does  there exist some new form of energy, so-called ‘Dark Energy?’ Lindsey seeks to answer such questions by studying of clusters of galaxies — the largest gravitationally-bound systems in the universe. Their abundance is a powerful cosmological probe as it depends upon both the expansion history of the universe and the growth of density fluctuations. A member of the South Pole Telescope collaboration, her research interests also include large-scale structure, the cosmic microwave background, and the development of bolometric detectors for measurements of the millimeter-wave sky. Lindsey received her PhD from the University of Chicago in 2013 and BA from Kenyon College in 2005.

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Clarence Chang

Clarence’s interests focus on observational cosmology with a particular emphasis on developing new superconducting technology for use in new experiments. He is part of a joint Chicago/Argonne superconducting detector development collaboration which is developing and building the focal plane for the upcoming SPT-3G experiment. This focal plane, with over 16,000 polarization sensitive detectors, will enable the South Pole Telescope to observe 2500 square degrees with unprecedented sensitivity. SPT-3G will explore the physics of inflation, dark energy, and the cosmic neutrino background.

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JD Emberson

JD has a broad interest in computational cosmology. His research is focused on the development and application of numerical techniques for large-scale cosmological structure formation. This includes both N-body as well as hydrodynamic simulations in order to gain insight into various astrophysical problems including dark energy, neutrinos, substructure, and reionization. Along with Nick Frontiere, he is leading the effort on the new hydrodynamics capability in the HACC code.

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Salman Habib

Aside from being a member of CPAC, Salman Habib also leads Argonne’s Computational Science Division (CPS). He holds joint appointments at the University of Chicago and Northwestern University. Salman’s research interests span astrophysics and cosmology, accelerator physics, classical and quantum dynamical systems and control theory, advanced statistical methods and machine learning, condensed matter physics, atomic and quantum optics, nonequilibrium field theory, and particle physics. Within cosmology, his current focus is on studies of dark energy, dark matter, neutrinos, and primordial fluctuations. This work involves a number of research directions at the interface of cosmological physics, advanced statistical methods, machine learning, and parallel supercomputing. Salman is the PI for the DOE ASCR ExaSky project that is preparing HACC for coming exascale supercomputers; he has led the HACC team since its first incarnation at Los Alamos.

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Andrew Hearin

Andrew’s research interests are at the intersection of cosmology and galaxy formation. He develops techniques to analyze large-scale structure data from present and near-future galaxy surveys aimed at uncovering the physical nature of dark matter and dark energy. Andrew’s focus is on transforming cosmological simulations into synthetic skies of gas and galaxies, so that simulations can be used as direct cosmological inference engines.

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Katrin Heitmann

Katrin Heitmann, CPAC Group Leader, is a Physicist and Computational Scientist at Argonne National Laboratory in the High Energy Physics and Mathematics and Computer Science Divisions. She is also a Senior Member of the Kavli Institute for Cosmological Physics at the University of Chicago. Before joining Argonne, Katrin was a staff member at Los Alamos National Laboratory. Her research currently focuses on computational cosmology, in particular on trying to understand the causes for the accelerated expansion of the Universe. She is responsible for large simulation campaigns with HACC and for the tools in the associated analysis library, CosmoTools. Katrin is a member of several major astrophysical surveys that aim to shed light on this question and is the computing coordinator for the Large Synoptic Survey Telescope Dark Energy Science Collaboration.

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Eve Kovacs

Eve’s research interests are focused on understanding the galaxy-halo connection and the simulation and validation of mock galaxy catalogs for upcoming sky surveys such as LSST. She is a member of DES and LSST-DESC. Eve is also interested in supernova cosmology, and in particular, the photometric classification of supernovae using machine-learning techniques.

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Patricia Larsen

Patricia’s interests focus mainly on measurements of weak lensing in cosmological surveys. In particular she has worked on combining weak lensing measurements of the CMB and cosmic shear, and on understanding astrophysical systematics affecting weak lensing surveys, including galaxy intrinsic alignments.

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Adrian Pope

Adrian Pope is a member of Argonne’s CPS Division. He has studied the large-scale structure of the Universe dating back to his work as an undergraduate (and after) on the Sloan Digital Sky Survey. Adrian plays a leading role in the development of HACC, beginning with the initial code prototype that ran on Roadrunner at Los Alamos, the first machine to break the petaflop barrier. He is currently investigating the optimization of HACC kernels on Aurora 2021, planned to be the first exascale system in the US, and expected to arrive at Argonne in 2021. Adrian also has interests in applications of advanced statistical methods in cosmology.

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Thomas Uram

Tom is a software engineer at the ALCF with extensive experience in software projects that involve high performance computing. He is the main developer of Balsam, an HPC workflow and edge service for running a large number of jobs on HPC systems. Tom has a leadership role in software management for HACC’s CosmoTools library; he has also led the work in making simulation data widely available through Argonne’s Petrel Data Pilot project.

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Gensheng Wang

Gensheng Wang is a physicist working on astrophysical instrumentation. His major achievements have been the delivery of a large array of superconducting bolometers for the SPT-3G project and the delivery of absorber coupled superconducting bolometers for the SPTpol project. His current work includes superconducting bolometric detector R&D for CMB-S4; physics and technology of superconducting detectors for astrophysics, nuclear physics, and particle physics; superconducting electronics for detector multiplexing; and laboratory instrument construction..



Alex Alarcon Gonzalez

Alex is a cosmologist with interest in the study of the expansion and growth history of the Universe using data from galaxy surveys and cosmological simulations. In particular, he wants to analyze the physics responsible for the formation of structures using numerical simulations in order to model observables related to cosmological inference. He has worked in the analysis of galaxy clustering measurements and photometric redshift error estimation and calibration to extract unbiased cosmological information from lensing surveys.

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Michael Buehlmann
Michael Buehlmann

Michael is a computational cosmologist with a broad interest in large-scale structure formation. His work is focused on the development and application of numerical methods to run and analyze large simulations of our Universe. Together with Nick Frontiere and JD Emberson, he is working on extending the baryonic physics models in the HACC simulation code.

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Nicholas Frontiere

Nick has wide interests in physics and computational science. He has worked on computational research projects at National Laboratories for many years. Nick has made many contributions to HACC (in particular the GPU version) and its analysis tools, beginning with work as an undergraduate on the HACC 3-D parallel FFT, now available separately as the DOE ECP-supported SWFFT package. He has played a leading role in the development of a new smoothed particle hydrodynamics (SPH) method, Conservative Reproducing Kernel SPH (CRK-SPH), that overcomes many of the problems of the original SPH technique, while maintaining many of its advantages. Nick is leading the work on the hydro version of the HACC code (with JD) and in the incorporation of a number of subgrid models.

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Riccardo Gualtieri

Riccardo is a cosmologist with a strong background in instrumentation, detectors and readout. He is interested in understanding the early Universe through the study of the Cosmic Microwave Background and its polarization. He is actively involved in the SPT-3G collaboration leading the low-ell BB spectrum analysis. Member of the SPIDER collaboration, Riccardo works on data analysis and instrument preparation for the second flight. As a member of CMB-S4 Riccardo works in the readout working group, at Argonne he is leading the readout testbed development and deployment under the supervision of Amy Bender.

Zhaodi Pan

Zhaodi is an experimental cosmologist working on millimeter-wavelength instrumentation and data analysis. Zhaodi works across the boundaries of hardware building, instrument calibration, astrophysical observation, data reduction, and scientific interpretation. Prior to joining Argonne he worked on building and characterizing a prototype spectrometer for the proposed NASA explorer-class mission PIXIE. He also worked on optical characterizations for detectors used for SPT-3G. Now his research focuses on two aspects of cosmology. 1) developing next-generation detectors and material characterization for these new detectors. 2) the gravitational lensing data analysis to constrain the growth of the structure of the universe.

Nesar Ramachandra

Nesar Ramachandra is a cosmologist with interests in the dynamics of large-scale structure formation; he is also working on the implementation of state of the art statistical and machine learning methods for cosmological data analysis and fast prediction tools (emulators) as part of the SciDAC-4 project led by CPAC.

Esteban Rangel

Steve Rangel is a computer scientist with broad interests in solving large-scale data analysis problems using HPC platforms. He is the main developer of HACC’s halo merger tree construction and analysis framework, using a new algorithm that employs the recently developed ‘core-tracking’ methodology. Steve also led work on a new parallel tessellation-based density estimation code that is now being used for work on weak and strong gravitational lensing (with Patricia). Steve is now also working on HACC’s implementation on exascale platforms.

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Antonia Sierra Villarreal

Sierra’s research interest lies in better understanding and quantifying the connections between simulations and the phenomenological understanding that can be gleaned from these to the observable universe. This manifests in the study of halo assembly bias as a function of the choice of halo definition, determining how much potential bias in cosmological parameters can arise from underlying dark matter power spectra assumptions, and aiding in the generation of simulated images for future surveys as the Vera Rubin LSST. Sierra is a builder in the LSST Dark Energy Science Collaboration and recipient of the 2021 NERSC Award for Innovation in high Performance Computing.

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Xiaofeng Dong

Xiaofeng is a starting graduate student from UChicago. He is currently working on implementing radiatiave cooling and AGN feedback into numerical simulations with advanced computing methods, and is beginning theoretical explorations of cosmological large scale structure formation problems.

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Xin Liu

Xin is a starting graduate student in CPAC. She is generally interested in computational cosmology. In particular, her main focus at the moment lies in using simulation and data analysis as tools to help her get a deeper understanding of cosmological problems.



Mae Warren

Mae is responsible for keeping CPAC running, in particular, all the main administrative tasks, including travel, purchase requests, various Argonne requirements, and supporting CPAC visitors. She is also responsible for helping to organize meetings and workshops, and maintaining the associated websites.
Administrative Secretary
High Energy Physics Division
Argonne National Laboratory
9700 S. Cass Avenue
Bldg. 360
Argonne, IL 60439

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Recent Alumni

Jonas Chaves-Montero

As a postdoc at CPAC, Jonas’ research focused on the study of the distribution of galaxy positions and velocities at large scales, and how to use this information to obtain a better understanding of the dark side of the Universe — dark energy and dark matter. Jonas developed theoretical tools to extract unbiased cosmological information from galaxy surveys using numerical simulations of large-scale structure.

Hillary Child

As a graduate student at CPAC, Hillary’s research focused on the evolution of dark matter halos in simulations, on modeling the redshift dependence of the concentration-mass relation, and understanding how the concentration of a halo changes as it grows. She also developed techniques using the bispectrum to improve measurements of the baryon acoustic oscillations (BAO) length scale.
Hal Finkel

Hal Finkel graduated from Yale University in 2011 with a Ph.D. in theoretical physics focusing on numerical simulation of early-universe cosmology. He was the Lead for Compiler Technology and Programming Languages at the ALCF. Hal has contributed to the LLVM compiler infrastructure project for many years and is currently the code owner of the PowerPC backend and the pointer-aliasing-analysis subsystem, among others. He is the lead developer on the bgclang project, which provides LLVM/Clang on the IBM Blue Gene/Q supercomputer, and represents Argonne on the C++ Standards Committee. Hal also helps develop the Hardware/Hybrid Accelerated Cosmology Code (HACC), a two-time IEEE/ACM Gordon Bell Prize finalist. He has designed and implemented a tree-based force evaluation scheme and the I/O subsystem and contributed to many other HACC components.

Martina Gerbino

As a postdoc at CPAC, Martina Gerbino worked as a theoretical cosmologist at the interface between theory and observations, with a particular focus on testing fundamental physics theories against data. Her research spanned a wide range of phenomenological investigations of theoretical models with a main focus on neutrino physics to CMB data analysis and interpretation. She also made significant research contributions in her work as a member of the Planck, Simons Observatory and CMB-S4 collaborations.

Joe Hollowed

As a postbac at CPAC, Joe’s work focused on the construction of synthetic galaxy catalogs and associated lightcones, providing simulation support for cluster cosmology studies, and large-scale structure research within the SPT and Vera Rubin Observatory LSST DESC.

Dan Korytov

As a graduate student at CPAC, Dan’s research focused on the connection between galaxies and dark matter halos. Dan helped developed a novel method of determining galaxy positions by explicitly tracking simulation particles (‘core-tracking’), designed to improve the robustness of dark matter substructure identification and the quality of models of satellite galaxy evolution. Dan’s cosmology research also played a key role in the development of cosmoDC2, the principal synthetic galaxy catalog used in Data Challenge 2 of the Vera Rubin Observatory LSST DESC.
Gabe Lynch

As a postbac at CPAC, Gabe’s work focused on cosmological simulations of Bose-Einstein condensate dark matter (BEC), involving the development of a spectral Schrödinger-Poisson solver using SWFFT, the 3D distributed FFT developed for the ExaSky project. Gabe’s research is motivated by the goal of deepening our understanding of structure formation in BEC dark matter models, as well as providing a useful tool to validate traditional n-body codes.
Malin Renneby

As a postdoc at CPAC, Malin’s research focused on how to statistically constrain the galaxy-halo relation through cosmic time with weak lensing and galaxy clustering with semi-analytical models of galaxy formation and hydrodynamical simulations, and on characterizing the imprint of baryonic processes such as AGN feedback on halo profiles and clustering amplitudes.
Imran Sultan

As a postbac at CPAC, Imran’s work focused on the substructure of dark matter halos in the HACC simulations, and understanding how satellite galaxy evolution can be predicted by applying additional modeling to a HACC core catalog: a record of the central particles of halos identified in a simulation.
Vinu Vikram

As a postdoc at CPAC, Vinu’s work focused on developing new tests of whether LCDM provides the correct theory of gravity on cosmological scales, and on measuring the baryonic mass contents of the universe with observations of the CMB.