Flavoured Lattice Schwinger Model with Chiral Anomaly

Abstract: We introduce the \emph{flavoured lattice Schwinger model}, a $(1{+}1)$-dimensional $U(1)$ lattice gauge theory in which the fermion doubling problem is resolved by staggering a $\mathbb{Z}{2}$ flavour degree of freedom rather than staggering chirality. Unlike all standard approaches, the flavoured construction preserves an exact axial $U(1)$ symmetry at finite lattice spacing. We derive the continuum limit, showing the model reduces to two copies of the massless Schwinger model labelled by $α\in{0,1}$. The central result is that the flavoured construction admits a well-defined, regularized, gauge-invariant lattice axial charge $Q{G}^{A}$ with chiral anomaly equation $\langle dQ_{G}^{A}/dt\rangle = -(2g/π)\int dx\,\langle E(x)\rangle$ in the continuum limit, derived as a direct dynamical consequence of minimal gauge coupling at finite lattice spacing. Restricting to the $α=0$ sector recovers the standard single-flavour result. We further show that spatial separation of the flavour sectors can be realised as a helical edge states living on the boundaries of a ribbon shaped $(2{+}1)$-dimensional Bernevig--Hughes--Zhang topological insulator. This provides a bulk-boundary picture solution to both the chiral anomaly and fermion doubling.