Theoretical Astrophysics
Overview
Theoretical astrophysics is a major area of research at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), encompassing work on high-energy neutrinos, cosmic rays, gamma rays, dark matter, black holes, and the most extreme environments in the universe. Together with other researchers, students, and postdoctoral scholars at WIPAC, these scientists develop theoretical models and interpret data from experiments such as IceCube, HAWC, and future observatories, helping to advance our understanding of the high-energy universe.
Research Topics
- High-energy neutrinos and neutrino astronomy
- The origins and acceleration of cosmic rays
- Gamma-ray and multimessenger astrophysics
- Dark matter and physics beyond the Standard Model
- Black holes, compact objects, and extreme astrophysical environments
Senior Personnel
- Ke Fang — origins of cosmic rays and neutrinos, particle acceleration in extreme astrophysical systems, and multimessenger signals from compact objects and transient phenomena
- Francis Halzen — neutrino astronomy and the IceCube Neutrino Observatory
- Dan Hooper — dark matter, cosmology, high-energy astrophysics, and particle theory, with a focus on connecting astrophysical observations to fundamental physics
Postdocs
Toni Bertolez-Martinez
Caleb Gemmel
Graduate Students
Arifa Khatee Zathul
Samyak Jain
Chen Li
Alisha Roberts
Angelina Sherman
Fabrizio Vassallo
WIPAC Contributions
WIPAC has played a leading role in the development of modern multimessenger astrophysics, combining expertise in experiment, instrumentation, data analysis, and theory to study the highest energy phenomena in the universe. WIPAC scientists have been central to the design, construction, and scientific operation of the IceCube Neutrino Observatory, the world’s largest neutrino detector, located at the South Pole. Since the discovery of a diffuse flux of astrophysical neutrinos in 2013, IceCube has opened an entirely new window on the universe, enabling the study of cosmic particle accelerators through neutrinos rather than only electromagnetic radiation. WIPAC researchers have also contributed extensively to gamma-ray astronomy through projects such as HAWC and the planned SWGO.
In addition to its experimental programs, WIPAC maintains a strong theoretical astrophysics effort focused on understanding the origin of cosmic rays, neutrinos, and gamma rays as well as the nature of dark matter and other physics beyond the Standard Model. WIPAC theorists develop models of particle acceleration in environments such as supernova remnants, active galactic nuclei, gamma-ray bursts, and compact-object systems while also interpreting data from observatories around the world. These efforts are closely integrated with WIPAC’s experimental activities, allowing theoretical predictions and observational measurements to directly inform one another.
WIPAC has also made important contributions in detector development, computing, and data science. Researchers and engineers at the center have developed advanced optical sensors, calibration systems, and large-scale data acquisition and analysis tools required for modern astroparticle physics experiments. Through collaborations spanning institutions across the United States and around the world, WIPAC continues to help shape the future of neutrino astronomy and high-energy astrophysics, training students and early-career scientists while advancing our understanding of the universe’s most energetic processes.
Select Publications
Can a breakdown of Hawking evaporation open a new mass for primordial black holes as dark matter?
G. Montefalcone, D. Hooper, K. Freese, C. Kelso, F. Kuhnel, and P. Sandick
Phys. Rev. D (2026), arXiv:2503.21005
journals.aps.org | arxiv.org
Cascaded Gamma-Ray Emission Associated with the KM3NeT Ultrahigh-energy Event KM3-230213A
K. Fang, F. Halzen, and D. Hooper
Astrophys. J. Lett. (2025), arXiv:2502.09545
iopscience.iop.org | arxiv.org
Supermassive primordial black holes from inflation
D. Hooper, A. Ireland, G. Krnjaic, and A. Stebbins
JCAP (2024), arXiv:2308.00756
iopscience.iop.org | arxiv.org
Neutrino and gamma-ray emissions from NGC 1068
C. Blanco, D. Hooper, T. Linden, and E. Pinetti
Phys. Rev. D (2025), arXiv:2307.03259
journals.aps.org | arxiv.org
Diffuse ultrahigh-energy gamma-ray emission from TeV halos
A. Dekker, I. Holst, D. Hooper, G. Leone, E. Simon, and H. Xiao
Phys. Rev. D (2024), arXiv:2306.00051
journals.aps.org | arxiv.org
Neutrinos from the Brightest Gamma-Ray Burst?
K. Murase, M. Mukhopadhyay, A. Kheirandish, S. Kimura, and Fang, Ke
Astrophys. J. Lett. (2022), arXiv:2210.15625
iopscience.iop.org | arxiv.org
The TeV Diffuse Cosmic Neutrino Spectrum and the Nature of Astrophysical Neutrino Sources
K. Fang, J. Gallagher, and F. Halzen
Astrophys. J. (2022), arXiv:2205.03740
iopscience.iop.org | arxiv.org
Multimessenger Implications of Sub-PeV Diffuse Galactic Gamma-Ray Emission
K. Fang and K. Murase
Astrophys. J. (2021), arXiv:2104.09491
iopscience.iop.org | arxiv.org
High-energy Neutrinos and Gamma Rays from Nonrelativistic Shock-powered Transients
K. Fang, B. Metzger, I. Vurm, E. Aydi, and L. Chomiuk
Astrophys. J. (2020), arXiv:2007.15742
iopscience.iop.org | arxiv.org
Severely Constraining Dark Matter Interpretations of the 21-cm Anomaly
A. Berlin, D. Hooper, G. Krnjaic and S. McDermott
Phys. Rev. Lett. (2018), arXiv:1803.02804
journals.aps.org | arxiv.org
High-Energy Neutrinos from Millisecond Magnetars formed from the Merger of Binary Neutron Stars
K. Fang and B. Metzger
Astrophys. J. (2017), arXiv:1707.04263
iopscience.iop.org | arxiv.org
Linking High-Energy Cosmic Particles by Black Hole Jets Embedded in Large-Scale Structures
K. Fang and K. Murase
Nature Phys. (2018), arXiv:1704.00015
nature.com | arxiv.org
HAWC Observations Strongly Favor Pulsar Interpretations of the Cosmic-Ray Positron Excess
D. Hooper, I. Cholis, T. Linden and K. Fang
Phys. Rev. D (2017), arXiv:1702.08436
journals.aps.org | arxiv.org
The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Case for Annihilating Dark Matter
T. Daylan, D. Finkbeiner, D. Hooper, et al
Phys. Dark Univ. (2016), arXiv:1402.6703
sciencedirect.com | arxiv.org
Testing the Newborn Pulsar Origin of Ultrahigh Energy Cosmic Rays with EeV Neutrinos
K. Fang, K. Kotera, K. Murase, and A. Olinto
Phys. Rev. D (2012), arXiv:1311.2044
journals.aps.org | arxiv.org
Newly-born pulsars as sources of ultrahigh energy cosmic rays
K. Fang, K. Kotera, and A. Olinto
Astrophys. J. (2012), arXiv:1201.5197
iopscience.iop.org | arxiv.org
Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
D. Hooper and L. Goodenough
Phys. Lett. B (2011), arXiv:1010.2752
sciencedirect.com | arxiv.org
GZK Neutrinos after the Fermi-LAT Diffuse Photon Flux Measurement
M. Ahlers, L. Anchordoqui, M. Gonzalez-Garcia, F. Halzen, and S. Sarkar
Astropart. Phys. (2010), arXiv:1005.2620
sciencedirect.com | arxiv.org
Pulsars as the Sources of High-Energy Cosmic-Ray Positrons
D. Hooper, P. Blasi, and P. Serpico
JCAP (2009), arXiv:0810.1527
iopscience.iop.org | arxiv.org
Particle astrophysics with high-energy neutrinos
T. Gaisser, F. Halzen, and T. Stanev
Phys. Rept. (1995, 1996), arXiv:hep-ph/9410384
sciencedirect.com | arxiv.org