On <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{c=1}$</EquationSource> </InlineEquation> critical phases in anisotropic spin-1 chains

Quantum spin-1 chains may develop massless phases in presence of Ising-like and single-ion anisotropies. We have studied c=1 critical phases by means of both analytical techniques, including a mapping of the lattice Hamiltonian onto an O(2) NL<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\sigma$</EquationSource> </InlineEquation>M, and a multi-target DMRG algorithm which allows for accurate calculation of excited states. We find excellent quantitative agreement with the theoretical predictions and conclude that a pure Gaussian model, without any orbifold construction, describes correctly the low-energy physics of these critical phases. This combined analysis indicates that the multicritical point at large single-ion anisotropy does not belong to the same universality class as the Takhtajan-Babujian Hamiltonian as claimed in the past. A link between string-order correlation functions and twisting vertex operators, along the c=1 line that ends at this point, is also suggested. Copyright Springer-Verlag Berlin/Heidelberg 2003