Quantum-group-invariant models: Bethe ansatz and finite-size spectrum
arXiv:2509.00610 · doi:10.1007/JHEP12(2025)117
Abstract
We consider the quantum integrable spin chain models associated with the Jimbo R-matrix based on the quantum affine algebra , subject to quantum-group-invariant boundary conditions parameterized by two discrete variables and . We develop the analytical Bethe ansatz for the previously unexplored case with any , and use it to investigate the effects of different boundary conditions on the finite-size spectrum of the quantum spin chain based on the rank- algebra . Previous work on this model with periodic boundary conditions has shown that it is critical for the range of anisotropy parameters , where its scaling limit is described by a non-compact CFT with continuous degrees of freedom related to two copies of the 2D black hole sigma model. The scaling limit of the model with quantum-group-invariant boundary conditions depends on the parameter : similarly as in the rank- chain, we find that the symmetry of the lattice model is spontaneously broken, and the spectrum of conformal weights has both discrete and continuous components, for . For , the latter coincides with that of the chain, which should correspond to a non-compact brane related to one black hole CFT in the presence of boundaries. For , the spectrum of conformal weights is purely discrete.
arXiv comment40 pages, typos fixed, appendix for R matrix added
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