LETTER: The lattice β-function of quantum spin chains

We derive the lattice β-function for quantum spin chains, suitable for relating finite temperature Monte Carlo data to the zero-temperature fixed points of the continuum nonlinear sigma model. Our main result is that the asymptotic freedom of this lattice β-function is responsible for the nonintegrable singularity in θ that prevents analytic continuation between θ = 0 and θ = π.