Group of Felix Yu

The research in my group focuses broadly on physics beyond the Standard Model, ranging from Z' physics, axions and axion-like particles, dark matter, charge-parity (CP) violation and quark and lepton flavor physics, Higgs physics, and new solutions to the hierarchy problem.

Z' physics

New U(1) symmetries provide a rich playground for exploring open questions in model building and motivating new avenues for experimental searches.  On the theoretical side, U(1) symmetries can involve non-trivial anomaly cancellation conditions, new marginal couplings such as kinetic mixing and scalar Higgs portals, gauge restrictions like the Stückelberg mechanism, and chiral fermion non-decoupling effects in loop processes.  For the experimental searches, new Z' gauge bosons provide attractive targets for the ATLAS and CMS experiments at the LHC, by virtue of the straightforward model parameters of coupling and mass.  My research involves both the theoretical and experimental aspects of U(1) gauge theories, ranging from calculating new interactions in chiral U(1)  models to interpreting recent collider constraints in the coupling vs. mass plane.

Axions and ALPs

The axion is a hypothetical new particle which is posited as the solution to the strong CP problem.  After the realization that non-Abelian gauge theories possess a possible CP-breaking parameter, experimental constraints from neutron electric dipole moments force the observable CP-violating parameter to be incredibly tiny.  By invoking Peccei-Quinn symmetry, a dynamical explanation for the smallness of this parameter is provided, predicting a very light, very weakly interacting particle known as the axion.  The research of our group focuses on determining the properties of the axion and related axion-like particles in non-minimal model constructions, taking advantage of the non-trivial ultraviolet dependence for axion couplings in effective field theories.

Dark matter and dark sectors

The mystery of dark matter is one of the biggest outstanding problems today in particle physics.  Synthesizing observations from cosmology and astrophysics, we see that dark matter overwhelms the matter budget of the universe, but without any positive laboratory signal for the detection of dark matter, we are completely ignorant about its particle properties.  Nevertheless, with a host of new experiments coming online in the coming years, including the upgraded MESA accelerator electron beam at Mainz and the associated experiments, there is hope that we will find signals for a new, very weakly interacting particle that could be solution to the dark matter problem.  My research focuses on the phenomenology of dark sector models with very weakly interacting particles and how to test them in the upcoming suite of terrestrial and astrophysical experiments.

CP violation and quark and lepton flavor physics

Another outstanding problem today in particle physics is the question of the matter-anti-matter asymmetry of the universe.  Since this necessarily involves new sources of CP violation, this question is intertwined with the theoretical study of the quark and lepton Yukawa interactions, which are responsible for fermion masses and flavor interactions.  My research focuses on the host of observables that can be and are being tested in low energy flavor experiments and high energy colliders and matching these observables to possible patterns of couplings in new physics flavor models.

Higgs physics

The Higgs boson, discovered in 2012 by the ATLAS and CMS experiments, provides a new window to probe very high scales of physics, where virtual corrections of new heavy particles give small modifications to Higgs couplings to the Standard Model particles.  One particularly exciting prospect currently being considered by the worldwide high energy physics community is building a next generation particle collider pinpointing the Higgs boson properties.  My research studies the possible Higgs phenomenology that can be studied at these colliders, including CP violating couplings and rare processes, and the impact of these measurements on underlying theories of new physics.

New solutions to the hierarchy problem

Recent models, such as the relaxion model and the clockwork mechanism, have attempted to address the longstanding hierarchy problem about the radiative stability of the weak scale.  Separately, traditional solutions, such as supersymmetry and composite Higgs sectors, have motivated many promising searches at particle physics but these searches have all returned null results.  My research focuses on the interplay between more speculative ideas about the hierarchy problem and the canonical collider tests for its resolution,