Critical Temperature Shift in Weakly Interacting Bose Gas

With a high-performance Monte Carlo algorithm we study the interaction-induced shift of the critical point in weakly interacting three-dimensional $|\psi|^4$-theory (which includes quantum Bose gas). In terms of critical density, $n_c$, mass, $m$, interaction, $U$, and temperature, $T$, this shift is universal: $\Delta n_c(T) = - C m^3 T^2 U$, the constant $C$ found to be equal to $0.0140 \pm 0.0005$. For quantum Bose gas with the scattering length $a$ this implies $\Delta T_c/T_c = C_0 a n^{1/3}$, with $C_0=1.29 \pm 0.05$.