Symmetric Mass Generation via Multicriticality in a 3D Lattice Gross–Neveu Model
We study the phase diagram of massless staggered fermions with two distinct four-fermion couplings, UB and UI, on a 3D Euclidean lattice using the fermion-bag Monte Carlo method. The model exhibits three phases: massless fermions (PMW), symmetry-broken massive (FM), and symmetric massive phases (PMS). For UB = 0, earlier work showed that one encounters a second-order PMW to PMS phase diagram, as the coupling UI is increased. Here, we find that the introduction of UB splits the above exotic transition into two conventional critical lines: a mean-field transition between the massless and broken phases (PMW to FM), and a 3D XY transition between the broken and symmetric massive phases (FM to PMS). Our work suggests that the critical point at UB = 0, which helps define the idea of symmetric mass generation in the continuum, may be viewed as a multicritical point.
