Theory Division

Astrophysics Theory

The Fermilab Theoretical Astrophysics Department consists of researchers who work at the confluence of astrophysics, cosmology, and particle physics. This field has been developing rapidly in recent years, with significant progress being achieved using astrophysical experiments and observatories to study the fundamental laws of nature. A striking example of this success has been the measurement of neutrino masses and mixing angles over the last few decades. More recently, the observation that the universe is expanding at an accelerating rate has fueled a great deal of research in the topic of dark energy. This, along with advances in areas including dark matter, cosmic rays, the cosmic microwave background, large scale structure, neutrino astronomy, gamma-ray astronomy, and axion astrophysics, has allowed the field of particle astrophysics to grow into one of the most important and active areas of particle physics research. Fermilab’s Theoretical Astrophysics Group has played a key role in the development of this exciting field and continues to be deeply involved in the connection between particle physics and astrophysics.

Nowhere is the connection between particle physics and astrophysics more evident than in the area of dark matter. Currently, the only evidence for dark matter comes from its gravitational interactions and, consequently, little is known about its particle nature. As astrophysical direct and indirect detection efforts develop, however, it may very well become possible to study the interactions and other properties of these particles. Furthermore, it may be possible to produce and study dark matter particles in collider experiments, such as the Large Hadron Collider. These efforts collectively represent a major thrust of the research being pursued at Fermilab.

A large portion of the department’s research involves simulations of various observable probes of cosmology, including large scale structure, galaxy clusters, supermassive black holes, gravitational lensing, and the Sunyaev-Zeldovich effects. These simulations help us to identify observable signatures that depend on the cosmological model that governs the underlying properties of the universe, and can in principle be used to extract information about fundamental physics. The simulations are then used to test signal extraction algorithms in the presence of simulated cosmological foregrounds and instrument effects that mimic some of the obstacles that observations must overcome in the real world.

Particle Theory

The Particle Theory Department of the Fermilab Theory Division studies all aspects of theoretical particle physics, especially those areas inspired by the experimental program—at Fermilab and elsewhere.

Several Fermilab experiments study neutrino properties, aiming to measure mixing angles and mass differences and test the three-generation paradigm of the Standard Model.  We are active in understanding the implications of current and recent experiments as well as projecting the future power of DUNE (in the U.S.) and HyperK (in Japan).  An important component of our research is a better understanding of the neutrino-nucleus scattering cross section, which is a multi-scale problem requiring a controlled understanding of quarks and gluons, nucleons, and atomic nuclei.  We have experts on all these topics, building on our other world-leading efforts on quantum chromodynamics (QCD).

Our colleagues researching lattice QCD have produced many results pertaining to quark-flavor physics, usually with unprecedented precision.  More recently, this expertise is being devoted to the hadronic contributions to the anomalous magnetic moment of the muon, in support of the ongoing Fermilab experiment.  They are also developing calculations of nucleon matrix elements to pin down the nucleon-level part of the neutrino-nucleus interaction.

Fermilab theorists have a long tradition in perturbative QCD, from seminal ideas to detailed calculations to event generators and textbooks.  After many years actively supporting the Tevatron program, our attention turned to CERN’s Large Hadron Collider, both the ongoing program and the new possibilities that will open up after the planned upgrades.  In particular, we enjoy a close working relationship with experimenters from CMS, via the LHC Physics Center.

The same can be said for our colleagues focused on the search for physics beyond the Standard Model at the LHC.  The efforts include model building, collider phenomenology, and common interests with the Astro Theory Department (such as dark matter and baryogenesis).  This theme of research also ties together some formal aspects of quantum field theory and a whole range of experiments—the muon anomalous magnetic moment, lepton flavor violation, unexplained anomalies in B physics, and (of course) neutrino experiments.

Quantum Theory

Theorists at Fermilab are working at the interface of quantum information science (QIS) and high energy physics (HEP). Quantum technologies are advancing at a rapid pace, and the renaissance in quantum science can be harnessed to address fundamental questions about Nature and the Universe. This is relevant both on the computational front and in quantum sensing.