Spin models in complex magnetic fields: a hard sign problem

Abstract

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.

8 pages, 3 figures, talk presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain

References in corpus (3)

• Simulating the All-Order Strong Coupling Expansion I: Ising Model Demo
• Worm algorithms for the 3-state Potts model with magnetic field and chemical potential
• Oscillating propagators in heavy-dense QCD

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