Critical spin chains and loop models with $PSU(n)$ symmetry

Starting with the Ising model, statistical models with global symmetries provide fruitful approaches to interesting physical systems, for example percolation or polymers. These include the $O(n)$ model (symmetry group $O(n)$) and the Potts model (symmetry group $S_Q$). Both models make sense for $n,...

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Main Author: Paul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert Saleur
Format: Article
Language:English
Published: SciPost 2025-01-01
Series:SciPost Physics
Online Access:https://scipost.org/SciPostPhys.18.1.033
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author Paul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert Saleur
author_facet Paul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert Saleur
author_sort Paul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert Saleur
collection DOAJ
description Starting with the Ising model, statistical models with global symmetries provide fruitful approaches to interesting physical systems, for example percolation or polymers. These include the $O(n)$ model (symmetry group $O(n)$) and the Potts model (symmetry group $S_Q$). Both models make sense for $n,Q∈ \mathbb{C}$ and not just $n,Q∈ \mathbb{N}$, and both give rise to a conformal field theory in the critical limit. Here, we study similar models based on the group $PSU(n)$. We focus on the two-dimensional case, where the models can be described either as gases of non-intersecting orientable loops, or as alternating spin chains. This allows us to determine their spectra either by computing a twisted torus partition function, or by studying representations of the walled Brauer algebra. In the critical limit, our models give rise to a CFT that exists for any $n∈\mathbb{C}$ and has a global $PSU(n)$ symmetry. Its spectrum is similar to those of the $O(n)$ and Potts CFTs, but a bit simpler. We conjecture that the $O(n)$ CFT is a $\mathbb{Z}_2$ orbifold of the $PSU(n)$ CFT, where $\mathbb{Z}_2$ acts as complex conjugation.
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spelling doaj-art-bbb48ea130054b62891415411b881f4f2025-01-27T11:47:54ZengSciPostSciPost Physics2542-46532025-01-0118103310.21468/SciPostPhys.18.1.033Critical spin chains and loop models with $PSU(n)$ symmetryPaul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert SaleurStarting with the Ising model, statistical models with global symmetries provide fruitful approaches to interesting physical systems, for example percolation or polymers. These include the $O(n)$ model (symmetry group $O(n)$) and the Potts model (symmetry group $S_Q$). Both models make sense for $n,Q∈ \mathbb{C}$ and not just $n,Q∈ \mathbb{N}$, and both give rise to a conformal field theory in the critical limit. Here, we study similar models based on the group $PSU(n)$. We focus on the two-dimensional case, where the models can be described either as gases of non-intersecting orientable loops, or as alternating spin chains. This allows us to determine their spectra either by computing a twisted torus partition function, or by studying representations of the walled Brauer algebra. In the critical limit, our models give rise to a CFT that exists for any $n∈\mathbb{C}$ and has a global $PSU(n)$ symmetry. Its spectrum is similar to those of the $O(n)$ and Potts CFTs, but a bit simpler. We conjecture that the $O(n)$ CFT is a $\mathbb{Z}_2$ orbifold of the $PSU(n)$ CFT, where $\mathbb{Z}_2$ acts as complex conjugation.https://scipost.org/SciPostPhys.18.1.033
spellingShingle Paul Roux, Jesper Lykke Jacobsen, Sylvain Ribault, Hubert Saleur
Critical spin chains and loop models with $PSU(n)$ symmetry
SciPost Physics
title Critical spin chains and loop models with $PSU(n)$ symmetry
title_full Critical spin chains and loop models with $PSU(n)$ symmetry
title_fullStr Critical spin chains and loop models with $PSU(n)$ symmetry
title_full_unstemmed Critical spin chains and loop models with $PSU(n)$ symmetry
title_short Critical spin chains and loop models with $PSU(n)$ symmetry
title_sort critical spin chains and loop models with psu n symmetry
url https://scipost.org/SciPostPhys.18.1.033
work_keys_str_mv AT paulrouxjesperlykkejacobsensylvainribaulthubertsaleur criticalspinchainsandloopmodelswithpsunsymmetry