Mass is a basic property of matter in physics. The origin of mass for matter particles is one of the most fundamental questions about our universe. The standard mechanism for fermions to acquire a mass is the Yukawa-Higgs mechanism, which is based on the spontaneous symmetry breaking via the condensation of a scalar Higgs field (that couples to the fermion field as a bilinear mass via the Yukawa coupling). The Yukawa-Higgs mechanism is responsible for the mass generation of fundamental fermions (leptons and quarks) in the Standard Model, a significant theoretical discovery acknowledged by the Nobel Prize in Physics 2013.
In the last few years, it was gradually realized that there is a new mechanism of mass generation for fermions without symmetry breaking or condensing any (fermion bilinear) Higgs field. This new mechanism is referred to as symmetric mass generation (SMG). The SMG mechanism relies on the non-perturbative interaction effect of fermions and goes beyond the conventional mean-field description of fermion mass generation in the Yukawa-Higgs theory. It is realized that the SMG has deep connections with interacting topological insulators, quantum anomaly cancellations, and deconfined quantum criticality. It also has strong implications for the lattice regularization for chiral gauge theories, which has been a long-standing problem in the lattice gauge theory. SMG has generated a broad research interest in condensed matter and high-energy physics communities.
Together with Juven Wang, we wrote a review paper on SMG, introducing SMG models, summarizing the current numerical results, unifying current field theory understandings, and presenting an overview of various features and applications of SMG.