Phase structure analysis of 2d lattice CP(1) model with $θ$ term using tensor renormalization group method

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Main Authors: Aizawa, Hayato, Takeda, Shinji, Yoshimura, Yusuke
Format: Preprint
Published: 2025
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author Aizawa, Hayato
Takeda, Shinji
Yoshimura, Yusuke
author_facet Aizawa, Hayato
Takeda, Shinji
Yoshimura, Yusuke
contents We investigate the phase structure of a two-dimensional lattice CP(1) model with a $θ$ term. In particular, we aim to identify a critical region expected to exist along a $θ=π$ line. To explore the phase structure non-perturbatively and avoid the sign problem, we employ the tensor renormalization group method. We make two improvements compared to previous tensor network studies. The first improvement involves refining the initial tensor. Specifically, we construct it using a quadrature method, which achieves higher accuracy compared to the conventional approach. The second improvement consists of analyzing the phase structure using the information of the conformal field theory, namely the central charge and the scaling dimensions, which can be accessed relatively easily via the tensor renormalization group method. Thanks to these improvements, we identify both the onset of the critical region, $β_{\rm c}=0.5952(8)$ and its universality class as the SU(2)${}_{k=1}$ Wess-Zumino-Witten model.
format Preprint
id arxiv_https___arxiv_org_abs_2510_06624
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Phase structure analysis of 2d lattice CP(1) model with $θ$ term using tensor renormalization group method
Aizawa, Hayato
Takeda, Shinji
Yoshimura, Yusuke
High Energy Physics - Lattice
High Energy Physics - Theory
We investigate the phase structure of a two-dimensional lattice CP(1) model with a $θ$ term. In particular, we aim to identify a critical region expected to exist along a $θ=π$ line. To explore the phase structure non-perturbatively and avoid the sign problem, we employ the tensor renormalization group method. We make two improvements compared to previous tensor network studies. The first improvement involves refining the initial tensor. Specifically, we construct it using a quadrature method, which achieves higher accuracy compared to the conventional approach. The second improvement consists of analyzing the phase structure using the information of the conformal field theory, namely the central charge and the scaling dimensions, which can be accessed relatively easily via the tensor renormalization group method. Thanks to these improvements, we identify both the onset of the critical region, $β_{\rm c}=0.5952(8)$ and its universality class as the SU(2)${}_{k=1}$ Wess-Zumino-Witten model.
title Phase structure analysis of 2d lattice CP(1) model with $θ$ term using tensor renormalization group method
topic High Energy Physics - Lattice
High Energy Physics - Theory
url https://arxiv.org/abs/2510.06624