Critical coupling and $Δ\langleϕ^2\rangle$ in three-dimensional $ϕ^4$ theory
We consider the $ϕ^4$ theory with $ϕ(x)\in\mathbb{R}$ in three Euclidean dimensions. For a variety of self-couplings $\hatλ$, the critical (bare) parameter $\hatμ_{0\mathrm{c}}^2(\hatλ)$ is determined where the lattice-regulated system changes from the symmetric phase to the broken phase. Next, we send the box volume to infinity and switch to a universal scheme; this yields $\hatμ_\mathrm{c}^2(\hatλ)$ for each simulated $\hatλ$. Finally, a continuum extrapolation gives $f_\mathrm{c}=\lim_{\hatλ\to0} \hatλ^2/\hatμ_\mathrm{c}^2(\hatλ)$, and we find $f_\mathrm{c} = 18.808(64)_{\mathrm{stat}}(45)_{\mathrm{sys}} = 18.808(78)_{\mathrm{tot}}$. In addition, $Δ\langleϕ^2\rangle_\mathrm{c}/λ= -0.00303(12)_{\mathrm{stat}}(12)_{\mathrm{sys}} = -0.00303(17)_{\mathrm{tot}}$ is determined in the combined continuum and infinite-volume limit.