Numerical extraction of crosscap coefficients in microscopic models for (2+1)D conformal field theory

Abstract

Conformal field theory (CFT) can be placed on disparate space-time manifolds to facilitate investigations of their properties. For (2+1)-dimensional [(2+1)D] theories, one useful choice is the real projective space $\mathbb{RP}^3$ obtained by identifying antipodal points on the boundary sphere of a three-dimensional ball. One-point functions of scalar primary fields on this manifold generally do not vanish and encode the so-called crosscap coefficients. These coefficients also manifest on the sphere as the overlaps between certain crosscap states and CFT primary states. Taking the (2+1)D Ising CFT as a concrete example, we demonstrate that crosscap coefficients can be extracted from microscopic models. We construct crosscap states in both lattice models defined on polyhedrons and continuum models in Landau levels, where the degrees of freedom at antipodal points are entangled in Bell-type states. By computing their overlaps with the eigenstates of many-body Hamiltonians, we obtain results consistent with those from conformal bootstrap. Importantly, our approach directly reveals the absolute values of crosscap overlaps, whereas bootstrap calculations typically yield only their ratios. Furthermore, we investigate the finite-size scaling of these overlaps and their evolution under perturbations away from criticality.

Figures (3)

• Figure 1: Schematics of crosscap states in (a) one-dimensional systems, (b) the icosahedron, (c) LLs on the sphere.
• Figure 2: Numerical results at the critical point. (a) Energy spectrum of the system with $N_{e}=18$. The ground state $\mathbb{I}$ and three primary states $\sigma,\epsilon,\epsilon'$ are indicated. Eigenstates with even and odd $Z_2$ parity are represented by magenta and blue colors, respectively. (b) Ground state crosscap overlaps. (c) Ratios between the $\epsilon$ state crosscap overlaps and the ground state crosscap overlaps. (d) Ratios between the $\epsilon'$ state crosscap overlaps and the ground state crosscap overlaps. The solid lines in panels (b-c) are linear fitting versus $1/N_{e}$ and the one in panel (d) is linear fitting versus $1/N^{2}_{e}$.
• Figure 3: Numerical results off the critical point. (a) Ground state crosscap overlaps for $h\in[3.14,3.18]$. (b) The same data in panel (a) plotted versus $(h-h_{c})R^{1.467}$. The solid lines in both panels are linear fitting results.