Behavior near $\hat{I}¸=\ddot{I}€$ of the mass gap in the 2D O(3) non-linear sigma model

Abstract

The validity of the Haldane's conjecture entails that the mass gap of the 2-dimensional O(3) non-linear sigma model with a $\hat{I}¸$-term must tend to zero as $\hat{I}¸$ approaches the value $\ddot{I}€$ by following a precise law. In the present paper we extract the related critical exponents by simulating the model at imaginary $\hat{I}¸$.

24 pages, LaTeX source and 5 eps figures