publications

2024

1. A Primer on Graph-Theoretic Models and Metrics: Using Graphs for Modeling and Assessing Robustness

   Lance Menthe, Joshua Steier, Katherine C Hastings, and 3 more authors

   2024

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2023

1. How generative AI could make existing election threats even worse

   Nicole Schneidman, and Christian Johnson

   Nov 2023

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2. International Opportunities and Technical Challenges for the Space Elevator

   Christian Johnson

   Journal of Science Policy & Governance, Mar 2023

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2022

1. Improving the Technical Requirements Development Process for Weapon Systems

   Lauren A Mayer, William Shelton, Christian Johnson, and 5 more authors

   Mar 2022

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2. Looking for lies: An exploratory analysis for automated detection of deception

   Marek Posard, Christian Johnson, Julia L Melin, and 2 more authors

   Mar 2022

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3. Bag-of-words algorithms can supplement transformer sequence classification & improve model interpretability

   Christian Johnson, and William Marcellino

   Mar 2022

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4. Disrupting deterrence: Examining the effects of technologies on strategic deterrence in the 21st century

   Michael J Mazarr, Ashley L Rhoades, Nathan Beauchamp-Mustafaga, and 8 more authors

   Mar 2022

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5. Forecasting End Strength in the U.S. Army Reserve: An Integrated Modeling Concept

   Katharina Ley Best, Jennifer Lamping Lewis, Christina Panis, and 3 more authors

   Jul 2022

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2021

1. Constraining Localized Vote Tampering in the 2020 US Presidential Election

   Christian Johnson

   In Great Plains Political Science Association Annual Meeting, Jul 2021

   Presented at the Great Plains Political Science Association annual meeting

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2. Army Analytic Capabilities: A Case Study Within Army Contracting Command and Its Implications

   William Marcellino, Christian Johnson, Amber Jaycocks, and 3 more authors

   Jul 2021

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3. An Exploratory Analysis of Trends in Text Data from Congressional Oversight Hearings

   Marek Posard, Hilary Reininger, and Christian Johnson

   Jul 2021

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4. Graph Theoretic Algorithms for the Ground Based Strategic Deterrent Program: Prioritization and Scheduling

   Lance Menthe, Bart E Bennett, Parousia Rockstroh, and 2 more authors

   Jul 2021

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5. Reining in COVID-19 disinformation from China, Russia, and elsewhere

   Christian Johnson, and William Marcellino

   RAND blog, Jul 2021

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6. Bad actors in news reporting: tracking news manipulation by state actors

   Christian Johnson, and William Marcellino

   Jul 2021

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7. Army Analytic Capabilities: A Case Study Within Army Contracting Command and Its Implications

   William Marcellino, Justin Grana, Jair Aguirre, and 3 more authors

   Jul 2021

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2020

1. Foreign interference in the 2020 election: Tools for detecting online election interference

   William Marcellino, Christian Johnson, Marek Posard, and 1 more author

   Jul 2020

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2019

1. Searching for New Physics with the Fermi Large Area Telescope

   Arne Christian Johnson

   University of California, Santa Cruz, Jun 2019

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2. Direct detection of primordial black hole relics as dark matter

   Benjamin V. Lehmann, Christian Johnson, Stefano Profumo, and 1 more author

   Journal of Cosmology and Astroparticle Physics, Oct 2019

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   If dark matter is composed of primordial black holes, such black holes can span an enormous range of masses. A variety of observational constraints exist on massive black holes, and black holes with masses below 1015 g are often assumed to have completely evaporated by the present day. But if the evaporation process halts at the Planck scale, it would leave behind a stable relic, and such objects could constitute the entirety of dark matter. Neutral Planck-scale relics are effectively invisible to both astrophysical and direct detection searches. However, we argue that such relics may typically carry electric charge, making them visible to terrestrial detectors. We evaluate constraints and detection prospects in detail, and show that if not already ruled out by monopole searches, this scenario can be largely explored within the next decade using existing or planned experimental equipment. A single detection would have enormous implications for cosmology, black hole physics, and quantum gravity.

3. Search for gamma-ray emission from p-wave dark matter annihilation in the Galactic Center

   Christian Johnson, Regina Caputo, Christopher Karwin, and 3 more authors

   Phys. Rev. D, May 2019

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2018

1. Search for Gamma-Ray Emission from Local Primordial Black Holes with the Fermi Large Area Telescope

   M. Ackermann, W. B. Atwood, L. Baldini, and 113 more authors

   The Astrophysical Journal, Apr 2018

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   Black holes with masses below approximately 1015 g are expected to emit gamma-rays with energies above a few tens of MeV, which can be detected by the Fermi Large Area Telescope (LAT). Although black holes with these masses cannot be formed as a result of stellar evolution, they may have formed in the early universe and are therefore called primordial black holes (PBHs). Previous searches for PBHs have focused on either short-timescale bursts or the contribution of PBHs to the isotropic gamma-ray emission. We show that, in cases of individual PBHs, the Fermi-LAT is most sensitive to PBHs with temperatures above approximately 16 GeV and masses 6 × 1011 g, which it can detect out to a distance of about 0.03 pc. These PBHs have a remaining lifetime of months to years at the start of the Fermi mission. They would appear as potentially moving point sources with gamma-ray emission that become spectrally harder and brighter with time until the PBH completely evaporates. In this paper, we develop a new algorithm to detect the proper motion of gamma-ray point sources, and apply it to 318 unassociated point sources at a high galactic latitude in the third Fermi-LAT source catalog. None of the unassociated point sources with spectra consistent with PBH evaporation show significant proper motion. Using the nondetection of PBH candidates, we derive a 99% confidence limit on the PBH evaporation rate in the vicinity of Earth, . This limit is similar to the limits obtained with ground-based gamma-ray observatories.