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Sub-leading conformal dimensions at the O(4) Wilson-Fisher fixed point

In this work we focus on computing the conformal dimensions $D(j_L,j_R)$ of local fields that transform in an irreducible representation of $SU(2) \times SU(2)$ labeled with $(j_L,j_R)$ at the $O(4)$ Wilson-Fisher fixed point using the Monte Carlo method. In the large charge expansion, among the sectors with a fixed large value of $j = {\rm max}(j_L,j_R)$, the leading sector has $|j_L-j_R| = 0$ and the sub-leading one has $|j_L-j_R| = 1$. Since Monte Carlo calculations at large $j$ become challenging in the traditional lattice formulation of the $O(4)$ model, a qubit regularized $O(4)$ lattice model was used recently to compute $D(j,j)$. Here we extend those calculations to the sub-leading sector. Our Monte Carlo results up to $j=20$ fit well to the form $D(j,j-1)-D(j) \sim λ_{1/2}/\sqrt{j} + λ_1/j + λ_{3/2}/j^{3/2}$, consistent with recent predictions of the large charge expansion. Taking into account systematic effects in our fitting procedures we estimate the two leading coefficients to be $λ_{1/2}=2.08(5)$, $λ_1=2.2(3)$.