Fractal dimension of critical clusters in theΦ44model

We study the d=4 O(4) symmetric nonlinear sigma model at the pseudocritical points for $8^4$–${28}^4$ lattices. The Fortuin-Kasteleyn-Coniglio-Klein clusters are shown to have fractal dimension ${\mathit{d}}_{\mathit{f}}$≃3—in accordance with the conjectured scaling relation involving the odd critical exponent δ. For the one cluster algorithm introduced recently by Wolff the dynamical critical exponent z comes out to be compatible with zero in this model.