Symmetric mass generation as a multicritical point with enhanced symmetry

TL;DR

This paper investigates a lattice fermion model revealing a multicritical point with enhanced symmetry, where different phase transitions merge, including a direct second-order transition between massless and symmetric massive phases.

Contribution

It demonstrates the existence of a multicritical point with enhanced symmetry in a lattice fermion model, unifying phase transitions with novel critical behavior.

Findings

Evidence for second-order critical points between phases

Identification of a multicritical point with enhanced symmetry

Observation of a direct second-order transition between massless and symmetric massive phases

Abstract

We explore the phase diagram of a lattice fermion model that exhibits three distinct phases: a massless fermion (MF) phase; a massive fermion phase with spontaneous symmetry breaking (SSB) induced by a fermion bilinear condensate; and a massive fermion phase with symmetric mass generation (SMG). Using the fermion-bag Monte Carlo method on large cubical lattices, we find evidence for traditional second-order critical points separating the first two and the latter two phases. Remarkably, these critical points appear to merge at a multicritical point with enhanced symmetry when the symmetry breaking parameter is tuned to zero, giving rise to the recently discovered direct second-order transition between the massless and symmetric massive fermion phases.