Spin models in complex magnetic fields: a hard sign problem
ETH Zürich, Institute for Theoretical Physics, Wolfgang-Pauli-Str. 27, CH-8093 Zürich, Switzerland
2 CERN, Theory Division, CH-1211 Geneva 23, Switzerland
3 University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland
* Speaker, e-mail: firstname.lastname@example.org
Published online: 26 March 2018
Coupling spin models to complex external fields can give rise to interesting phenomena like zeroes of the partition function (Lee-Yang zeroes, edge singularities) or oscillating propagators. Unfortunately, it usually also leads to a severe sign problem that can be overcome only in special cases; if the partition function has zeroes, the sign problem is even representation-independent at these points. In this study, we couple the N-state Potts model in different ways to a complex external magnetic field and discuss the above mentioned phenomena and their relations based on analytic calculations (1D) and results obtained using a modified cluster algorithm (general D) that in many cases either cures or at least drastically reduces the sign-problem induced by the complex external field.
© The Authors, published by EDP Sciences, 2018
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (http://creativecommons.org/licenses/by/4.0/).