 
Summary: The mass gap of the 2D O(3)
Heisenberg model at = from
simulations at imaginary
Bartolome Allés (INFN Pisa)
Alessandro Papa (Univ. Calabria)
ECT* Workshop, March 6, 2009, Trento
> PRD 77 056008 (2008) (arXiv:0711.1496)
> arXiv:0811.1528
Haldane, Affleck and others, showed that antiferromagnetic
1D chains of quantum spins present two kinds of large dis
tance correlations: exponentially falling if the spin s is
integer and powerlaw if s is halfinteger.
It was also shown that the 1D chain of quantum spins s
shares the same large distance physics than the 2D non
linear O(3) sigma model with a theta term q=2ps.
In particular, and due to the periodicity of the topological q
term, this equivalence should imply that the 2D O(3) non
linear sigma model with a q=p term must be massless.
Two recent numerical simulations (Bietenholz et al.,Azcoiti
et al.) suggest that the model undergoes a second order
