Schwinger Model with a Dynamical Axion

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Main Authors: Rouxinol, Gabriel, Magorsch, Tom, Osborne, Jesse J., Brambilla, Nora, Halimeh, Jad C.
Format: Preprint
Published: 2026
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author Rouxinol, Gabriel
Magorsch, Tom
Osborne, Jesse J.
Brambilla, Nora
Halimeh, Jad C.
author_facet Rouxinol, Gabriel
Magorsch, Tom
Osborne, Jesse J.
Brambilla, Nora
Halimeh, Jad C.
contents One of the major open puzzles in the Standard Model of particle physics is the strong CP problem: although Quantum Chromodynamics allows a CP-violating topological $θ$-term, experiments constrain its value to be extremely small. The Peccei--Quinn mechanism resolves this problem by promoting the $θ$-angle to a dynamical field-introducing the axion -- whose dynamics relax the effective angle $θ_\text{eff}$ to a CP-conserving minimum. Here, we investigate the resulting axion physics in a Hamiltonian lattice gauge theory (LGT) by coupling a quantized axion field to the massive Schwinger model with a topological $θ$-term. Using infinite matrix product state techniques, we compute the ground-state properties of the resulting theory and demonstrate that the axion dynamically relaxes $θ_\text{eff}$ to the minimum of the vacuum energy. Consequently, the ground-state energy becomes independent of $θ$, demonstrating the axion-mediated solution to the strong CP problem within a fully dynamical LGT. We further analyze CP restoration and extract the axion mass from the topological susceptibility and excitation spectrum. Our results provide a nonperturbative demonstration of axion dynamics in a quantum LGT amenable to investigation on modern quantum hardware.
format Preprint
id arxiv_https___arxiv_org_abs_2603_12194
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Schwinger Model with a Dynamical Axion
Rouxinol, Gabriel
Magorsch, Tom
Osborne, Jesse J.
Brambilla, Nora
Halimeh, Jad C.
High Energy Physics - Phenomenology
Quantum Gases
High Energy Physics - Lattice
High Energy Physics - Theory
Nuclear Theory
One of the major open puzzles in the Standard Model of particle physics is the strong CP problem: although Quantum Chromodynamics allows a CP-violating topological $θ$-term, experiments constrain its value to be extremely small. The Peccei--Quinn mechanism resolves this problem by promoting the $θ$-angle to a dynamical field-introducing the axion -- whose dynamics relax the effective angle $θ_\text{eff}$ to a CP-conserving minimum. Here, we investigate the resulting axion physics in a Hamiltonian lattice gauge theory (LGT) by coupling a quantized axion field to the massive Schwinger model with a topological $θ$-term. Using infinite matrix product state techniques, we compute the ground-state properties of the resulting theory and demonstrate that the axion dynamically relaxes $θ_\text{eff}$ to the minimum of the vacuum energy. Consequently, the ground-state energy becomes independent of $θ$, demonstrating the axion-mediated solution to the strong CP problem within a fully dynamical LGT. We further analyze CP restoration and extract the axion mass from the topological susceptibility and excitation spectrum. Our results provide a nonperturbative demonstration of axion dynamics in a quantum LGT amenable to investigation on modern quantum hardware.
title Schwinger Model with a Dynamical Axion
topic High Energy Physics - Phenomenology
Quantum Gases
High Energy Physics - Lattice
High Energy Physics - Theory
Nuclear Theory
url https://arxiv.org/abs/2603.12194