The Thirring Model in 2+1$d$ with Optimised Domain Wall Fermions

Abstract

After briefly reviewing the potential for the $N$-flavor Thirring model, formulated with reducible fermions in 2+1$d$, to exhibit a strongly-coupled UV-stable fixed point where U($2N$) symmetry is spontaneously broken by a fermion bilinear condensate, we present recent lattice studies using the Domain Wall Fermion formulation. In particular, we focus on possible improved methods for extracting the necessary $L_s\to\infty$ limit, where $L_s$ is the wall separation, through a combination of partial quenching (ie. $L_s({\rm valence})>L_s({\rm sea})$), replacing the Shamir kernel with the Wilson kernel in the definition of the overlap operator, and improved estimation of the signum function using the Zolotarev approximation. Equation of state fits for critical exponents on $12^3$ systems yield encouraging agreement between distinct approaches, consistent with universal scaling, while contradicting earlier fits based on a naive extrapolation. The new results are also in tension with old results obtained with staggered fermions.