About

The legacy of the slave family haunts the status of black Americans in modern U.S. society. Stereotypes that first entered the popular imagination in the form of plantation lore have continued to distort the African American social identity. In 'What Sorrows Labour in My Parents' Breast?', Brenda Stevenson provides a long overdue concise history to help the reader understand this vitally important African American institution as it evolved and survived under the extreme opposition that the institution of slavery imposed. The themes of this work center on the multifaceted reality of loss, recovery, resilience and resistance embedded in the desire of African/African descended people to experience family life despite their enslavement. These themes look back to the critical loss that Africans, both those taken and those who remained, endured, as the enslaved poet Phillis Wheatley honors in the line—'What sorrows labour in my parents’ breast?,' and look forward to the generations of slaves

Research topics

• Physics
• Astrophysics
• Astronomy
• Optics

Selected publications

• Machine Learning in Fundamental Physics: From Early Universe Signatures to QCD Evolution

  SMU Scholar (Southern Methodist University) · 2026-04-01

  articleOpen access1st authorCorresponding

  In both cosmology and small-x quantum chromodynamics, the relevant theoretical predictions are well-defined but expensive to evaluate repeatedly over broad parameter spaces or large ensembles of simulated data. The central question of this thesis is when machine learning can accelerate those calculations without weakening the reliability of the final physics conclusions. The thesis develops and tests this idea in three settings. First, it studies the Derivative Approximation for Likelihoods (DALI) as a means of diagnosing when Fisher-matrix forecasts cease to be trustworthy in cosmological parameter inference. Second, it investigates graph-based spherical neural networks for estimating primordial non-Gaussianity directly from simulated cosmic microwave background maps and benchmarks their performance against Fisher and Komatsu-Spergel-Wandelt estimator targets. Third, it constructs neutral-network surrogates for the Balitsky-Kovchegov equation in order to accelerate diploe-model calculations relevant to deep-inelastic scattering as small Bjorken-x. Across these projects, the main conclusion is methodological rather than a novel discovery. Machine learning is most useful here when it functions as a calibrated surrogate within a theory-first workflow. In that setting, the exact calculation remains the standard of truth; the learned model is trained against controlled numerical data, and performance is judged by physics-level validation rather than by generic machine-learning metrics alone. The results show that surrogate models can provide substantial computational gains in controlled regimes, but they must be paired with explicit validity tests and final cross-checks against higher-fidelity calculations before they are used to support scientific claims.

  Publisher

• VTSCat: The VERITAS Catalog of Gamma-Ray Observations

  Research Notes of the AAS · 2023-01-10 · 11 citations

  articleOpen access

  Abstract The ground-based gamma-ray observatory Very Energetic Radiation Imaging Telescope Array System (VERITAS, https://veritas.sao.arizona.edu/ ) is sensitive to photons of astrophysical origin with energies in the range between ≈85 GeV and ≈30 TeV. The instrument consists of four 12 m diameter imaging Cherenkov telescopes operating at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS started four-telescope operations in 2007 and collects about 1100 hr of good-weather data per year. The VERITAS collaboration has published over 100 journal articles since 2008 reporting on gamma-ray observations of a large variety of objects: Galactic sources like supernova remnants, pulsar wind nebulae, and binary systems; extragalactic sources like star-forming galaxies, dwarf-spheroidal galaxies, and highly variable active galactic nuclei. This note presents VTSCat: the catalog of high-level data products from all VERITAS publications.

  PublisherDOI

• VTSCat: The VERITAS Catalog of Gamma-Ray Observations

  Zenodo (CERN European Organization for Nuclear Research) · 2023-01-23

  datasetOpen access

  VTSCat is the catalog of high-level data products from all publications of the VERITAS collaboration. The VTSCat data collection contains: high-level data like spectral flux points, light curves, spectral fits in human and machine-readable yaml and ecsv file format tabled data like upper limits tables from dark matter searches or results on the extragalactic background in ecsv file format sky maps (wherever available) in FITS file format A detailed description of VTSCat can be found in A. Acharyya et al 2023 Res. Notes AAS 7 6. Please check also the README file and all documentation linked to the README. VTSCat supplements the HEASARC catalogue of VERITAS results, accessible through this link. VTSCat is inspired and derived from gamma-cat. If you are a previous VERITAS author and would like to be associated with this repository, please send an email to G. Maier. Access: GitHub: https://github.com/VERITAS-Observatory/VERITAS-VTSCat HEASARC: https://heasarc.gsfc.nasa.gov/W3Browse/all/verimaster.html References: https://veritas.sao.arizona.edu/ VER Dictionary of Nomenclature: https://cds.u-strasbg.fr/cgi-bin/Dic-Simbad?/17350620 GitHub: https://github.com/VERITAS-Observatory/VERITAS-VTSCat HEASARC: https://heasarc.gsfc.nasa.gov/W3Browse/all/verimaster.html Research note A. Acharyya et al 2023 Res. Notes AAS 7 6; see also arXiv:2301.04498 ICRC 2021 proceedings: https://arxiv.org/abs/2108.06424

  PublisherDOI

• Beyond Fisher forecasting for cosmology

  Physical review. D/Physical review. D. · 2023-05-08 · 4 citations

  articleOpen access

  The planning and design of future experiments rely heavily on forecasting to assess the potential scientific value provided by a hypothetical set of measurements. The Fisher information matrix, due to its convenient properties and low computational cost, provides an especially useful forecasting tool. However, the Fisher matrix only provides a reasonable approximation to the true likelihood when data are nearly Gaussian distributed and observables have nearly linear dependence on the parameters of interest. Also, Fisher forecasting techniques alone cannot be used to assess their own validity. Thorough sampling of the exact or mock likelihood can definitively determine whether a Fisher forecast is valid, though such sampling is often prohibitively expensive. We propose a simple test, based on the derivative approximation for likelihoods (DALI) technique, to determine whether the Fisher matrix provides a good approximation to the exact likelihood. We show that the Fisher matrix becomes a poor approximation to the true likelihood in regions where two-dimensional slices of level surfaces of the DALI approximation to the likelihood differ from two-dimensional slices of level surfaces of the Fisher approximation to the likelihood. We demonstrate that our method accurately predicts situations in which the Fisher approximation deviates from the true likelihood for various cosmological models and several data combinations, with only a modest increase in computational cost compared to standard Fisher forecasts.

  PublisherOA PDFDOI

• Beyond Fisher Forecasting for Cosmology

  arXiv (Cornell University) · 2022-11-12

  preprintOpen access

  The planning and design of future experiments rely heavily on forecasting to assess the potential scientific value provided by a hypothetical set of measurements. The Fisher information matrix, due to its convenient properties and low computational cost, provides an especially useful forecasting tool. However, the Fisher matrix only provides a reasonable approximation to the true likelihood when data are nearly Gaussian distributed and observables have nearly linear dependence on the parameters of interest. Also, Fisher forecasting techniques alone cannot be used to assess their own validity. Thorough sampling of the exact or mock likelihood can definitively determine whether a Fisher forecast is valid, though such sampling is often prohibitively expensive. We propose a simple test, based on the Derivative Approximation for LIkelihoods (DALI) technique, to determine whether the Fisher matrix provides a good approximation to the exact likelihood. We show that the Fisher matrix becomes a poor approximation to the true likelihood in regions where two-dimensional slices of level surfaces of the DALI approximation to the likelihood differ from two-dimensional slices of level surfaces of the Fisher approximation to the likelihood. We demonstrate that our method accurately predicts situations in which the Fisher approximation deviates from the true likelihood for various cosmological models and several data combinations, with only a modest increase in computational cost compared to standard Fisher forecasts.

  PublisherOA PDFDOI

• Multiwavelength Observations of the Blazar VER J0521+211 during an Elevated TeV Gamma-Ray State

  The Astrophysical Journal · 2022-06-01 · 8 citations

  articleOpen access

  Abstract We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10 −7 photons m −2 s −1 , or ∼37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z ≤ 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object.

  PublisherOA PDFDOI

• Design and performance of the prototype Schwarzschild-Couder telescope camera

  Journal of Astronomical Telescopes Instruments and Systems · 2022-02-15 · 15 citations

  articleOpen access

  The prototype Schwarzschild-Couder Telescope (pSCT) is a candidate for a medium-sized telescope in the Cherenkov Telescope Array. The pSCT is based on a dual-mirror optics design that reduces the plate scale and allows for the use of silicon photomultipliers as photodetectors. The prototype pSCT camera currently has only the central sector instrumented with 25 camera modules (1600 pixels), providing a 2.68-deg field of view (FoV). The camera electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application-specific integrated circuits. Field programmable gate arrays sample incoming signals at a gigasample per second. A single backplane provides camera-wide triggers. An upgrade of the pSCT camera that will fully populate the focal plane is in progress. This will increase the number of pixels to 11,328, the number of backplanes to 9, and the FoV to 8.04 deg. Here, we give a detailed description of the pSCT camera, including the basic concept, mechanical design, detectors, electronics, current status, and first light.

  PublisherOA PDFDOI

• Detection of the Crab Nebula with the 9.7 m prototype Schwarzschild-Couder telescope

  Astroparticle Physics · 2021 · 28 citations

  • Physics
  • Astronomy
  • Astrophysics
  PublisherOA PDFDOI

• VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies

  The Astrophysical Journal · 2021 · 53 citations

  • Physics
  • Astrophysics
  • Astronomy

  Abstract The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of nonthermal radiation. The inner 375 pc × 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants (SNRs). We present the results of our improved analysis of the very-high-energy gamma-ray emission above 2 TeV from the GC using 125 hr of data taken with the Very Energetic Radiation Imaging Telescope Array System imaging-atmospheric Cerenkov telescope between 2010 and 2018. The central source VER J1745–290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level (38 σ ), and we report its spectrum and light curve. Its differential spectrum is consistent with a power law with exponential cutoff, with a spectral index of , a flux normalization at 5.3 TeV of TeV −1 cm −2 s −1 , and cutoff energy of TeV. We also present results on the diffuse emission near the GC, obtained by combining data from multiple regions along the GC ridge, which yield a cumulative significance of 9.5 σ . The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 ± 0.20, showing no evidence of a cutoff up to 40 TeV. This strengthens the evidence for a potential accelerator of PeV cosmic rays being present in the GC. We also provide spectra of the other sources in our field of view with significant detections, composite SNR G0.9+0.1, and HESS J1746–285.

  PublisherOA PDFDOI

• The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies

  The Astrophysical Journal · 2020 · 43 citations

  • Physics
  • Astrophysics
  • Astronomy

  Abstract We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ -rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ -rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ -ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ -ray ( Fermi -LAT), X-ray ( Swift , Rossi X-ray Timing Experiment , MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsähovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare “decline” epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25–55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor ( δ ≳ 33) and the size of the emission region ( ) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux–flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.

  PublisherOA PDFDOI

Frequent coauthors

• D. Kieda

  34 shared

• R. Mukherjee

  33 shared

• A. N. Otte

  Georgia Institute of Technology

  33 shared

• V. Vagelli

  33 shared

• T. B. Humensky

  Goddard Space Flight Center

  32 shared

• Q. Feng

  University of California, Berkeley

  32 shared

• D. Ribeiro

  31 shared

• A. Gent

  Emory University

  30 shared

Education

• PhD, Physics

  Southern Methodist University

  2026

• Masters, Physics

  Southern Methodist University

  2023

Awards & honors

• James A. Rawley Prize from the Organization of American Hist…
• Ida B. Wells Barnett Award for Bravery in Journalism
• Gustavus Meyer Outstanding Book Prize for Life in Black and…
• John Simon Guggenheim Memorial Fellowship (2015-2016)
• American Academy in Berlin Fellowship (Spring 2016)