Yonatan Frederick Kahn

Assistant Professor


Yonatan Frederick Kahn

Primary Research Area

  • High Energy Physics
415 Loomis Laboratory

For more information


Yonatan Kahn is a theoretical physicist whose research is focused on dark matter and its detection strategies. Professor Kahn received his Ph.D. in 2015 from MIT, under the supervision of Jesse Thaler. He holds degrees in music, physics, and mathematics from Northwestern University (B.A., B.Mus 2009) and completed Part III of the Mathematical Tripos with Distinction at the University of Cambridge in 2010 supported by a Churchill Scholarship. He previously held postdoctoral positions at the Kavli Institute for Cosmological Physics (KICP) at the University of Chicago and Princeton University. Professor Kahn joined the faculty of the University of Illinois in 2019.

Research Statement

I'm a theoretical physicist on the hunt for dark matter. Of all the mass energy in the universe, the particles comprising everything we've ever measured or observed directly -- stars, planets, interstellar gas, all life on Earth -- make up only 15% of the cosmic pie chart. The vast majority of the mass of the universe has only been observed indirectly, and has been dubbed dark matter. Despite this, the gravitational effects of dark matter are numerous and profound, and many independent measurements have all converged on a remarkably consistent story: there exists some stuff in the universe which feels the gravitational force but not the electromagnetic or strong nuclear forces, to any appreciable extent.

The problem is, we know next to nothing about dark matter apart from the fact that it's out there. How much does it weigh? Does it interact with itself, or weakly with ordinary particles? Are there multiple species of dark matter, perhaps analogous to the proton, neutron, and electron which make up ordinary matter? Much effort has focused on a particular scenario: dark matter weighing about as much as an atomic nucleus, interacting with atomic nuclei via the weak nuclear force, and consisting of just a single particle species. This kind of dark matter is known as a WIMP, or weakly-interacting massive particle, and it's a beautiful theory: with a minimal number of moving parts, it predicts exactly the right amount of dark matter, and is tied to both the Standard Model and supersymmetry. Alas, the simplest explanation is not guaranteed to be the correct one. Dozens of experiments have searched for this particle -- passing through the Earth, annihilating at the center of the galaxy, or being produced in particle colliders -- to no avail. The WIMP scenario is certainly not ruled out, but it is becoming highly constrained.

I'm interested in exploring theories of dark matter beyond the WIMP: lighter particles (MeV-scale or sub-eV scale, in particle physics units), particles with different interactions (a dark photon rather than the weak nuclear force, or with electrons rather than nuclei), or multiple species of particles. Each of these theories would give different experimental signatures, and my research is focused on proposing experiments to look for these different kinds of dark matter. I'm especially drawn to the creativity and open-mindedness required to find just the right experimental avenue to detect these particles, and also to the possibility of collaboration between different fields of science (neutrino physics, condensed matter, physical chemistry, plasma physics, materials science) to develop the right equipment to build the experiment. As an example, I proposed a search for axion dark matter that soon grew into the ABRACADABRA collaboration, which has recently taken its first data. I believe discovering the identity of dark matter is the most pressing question in particle physics which is likely to be resolved on a 50-year timescale, and I want to help cover all the bases in case dark matter is hiding in a place we least expected it.

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  • In the Media
  • Research

The theory behind dark matter detection dates back to a 1985 paper that considered how a neutrino detector could be repurposed to look for particles of the substance. The study proposed that an incoming dark matter particle could hit an atomic nucleus in the detector and give it a kick—similar to one billiard ball crashing into another. This collision would transfer momentum from the dark matter, walloping the nucleus hard enough to make it spit out an electron or a photon.

At high energies, this picture is essentially fine. Atoms in the detector can be thought of as free particles, discrete and unconnected to one another. At lower energies, however, the picture changes.

“Your detectors are not made of free particles,” says Yonatan (Yoni) Kahn, a dark matter theorist at the University of Illinois at Urbana-Champaign and a co-author of the first paper. “They’re just made of stuff. And you have to understand the stuff if you want to understand how your detector actually works.”

  • Faculty Highlights
  • High Energy Physics

Yoni's research asks questions such as “What is the mass of the dark matter particle,” “What other particles that we know of does it interact with,” and “How was it created in the early universe”?