Theta-point polymers in the plane and Schramm-Loewner evolution

We study the connection between polymers at the theta temperature on the lattice and Schramm-Loewner chains with constant step length in the continuum. The second of these realize a useful algorithm for the exact sampling of tricritical polymers, where finite-chain effects are excluded. The driving function computed from the lattice model via a radial implementation of the zipper method is shown to converge to Brownian motion of diffusivity kappa = 6 for large times. The distribution function of an internal portion of walk is well approximated by that obtained from Schramm-Loewner chains. The exponent of the correlation length nu and the leading correction-to-scaling exponent Delta(1) measured in the continuum are compatible with nu = 4/7 (predicted for the theta point) and Delta(1) = 72/91 (predicted for percolation). Finally, we compute the shape factor and the asphericity of the chains, finding surprising accord with the theta-point end-to-end values.