Improved TCSA convergence from a missing scalar primary

Establish whether including the missing scalar primary expected near scaling dimension $\Delta\approx 9$ improves the convergence of the Truncated Conformal Space Approach for the three-dimensional Ising Field Theory mass gap.

Background

The TCSA mass gap improves as the truncation is enlarged up to approximately $\Delta_{\rm max}=7$, but then shows little further improvement through the included descendant cutoff at $\Delta_{\rm max}=11.71$. The authors attribute this behavior tentatively to the omission of a scalar primary whose dimension may be near 9 and whose OPE data are not currently available. They explicitly conjecture that adding this operator would improve convergence, leaving the conjecture unresolved.