  We study the O(4) Wilson-Fisher fixed point in 2+1 dimensions in fixed
large-charge sectors identified by products of two spin-j representations
$(j_L, j_R)$. Using effective field theory we derive a formula for the
conformal dimensions $D(j_L, j_R)$ of the leading operator in terms of two
constants, $c_{3/2}$ and $c_{1/2}$, when the sum $j_L + j_R$ is much larger
than the difference $|j_L-j_R|$. We compute $D(j_L,j_R)$ when $j_L = j_R$ with
Monte Carlo calculations in a discrete formulation of the O(4) lattice field
theory, and show excellent agreement with the predicted formula and estimate
$c_{3/2}=1.068(4)$ and $c_{1/2}=0.083(3)$.
