arXiv subjects

Soma Onoda

Publications and source records attributed to Soma Onoda.

15 recordsLinked to original sources

arXiv2026

Lattice chiral non-Abelian gauge symmetry via bosonization

A central issue in lattice formulations of chiral gauge theories is how the anomaly cancellation mechanism of the continuum theory can be realized at finite lattice spacing. In the present paper, based on non-Abelian bosonization, we propose a lattice formulation of the bosonic theory corresponding to a two-dimensional non-Abelian chiral gauge theory. In the continuum theory, the gauge anomaly of chiral fermions is represented, in the bosonized description, as anomaly inflow from a three-dimensional Chern--Simons-type bulk contribution contained in a gauged Wess--Zumino--Witten model. Motivated by this structure, we introduce gauge-neutral spectator fermions and use the resulting bosonized description. We then construct a lattice counterpart of the gauged Wess--Zumino--Witten model with a three-dimensional bulk extension under appropriate smoothness conditions. A salient feature of this lattice formulation is the cancellation of the left and right bulk contributions in the exponentiated action. This cancellation occurs even before taking the continuum limit when the anomaly-free condition is satisfied, namely when the left and right representations have identical quadratic indices. Thus, the present construction realizes the anomaly-cancellation mechanism at finite lattice spacing via the bosonized description of two-dimensional anomaly-free chiral gauge theories. Establishing the desired continuum limit remains an important open problem.

hep-lat↗

arXiv2026

Eigenstate Thermalization Hypothesis with projective representation

The Eigenstate Thermalization Hypothesis (ETH) provides a sufficient condition for thermalization of isolated quantum systems. While the standard ETH is formulated in the absence of degeneracy, physical systems often possess symmetries that induce degenerate energy eigenstates. In this paper, we investigate ETH in the presence of nontrivial projective representations of Abelian symmetries, which arise naturally from 't~Hooft anomalies. We argue that such projective structures can lead to degenerate excited states, and how the ETH can be formulated under such degeneracies. In the presence of projective charges supplied by symmetry operators, our projective-representation ETH indicates that the stationary values of the operators are described by the generalized Gibbs ensemble instead of the standard Gibbs ensemble. Our findings elucidate the role of symmetry and degeneracy in quantum thermalization and pave the way for further exploration of the ETH in anomalous symmetry settings.

hep-th↗

arXiv2026

Geometric phase from encircling an exceptional point of a quantum resonance in the complex-scaling method

Non-Hermitian operators are now routinely used to describe few-mode systems such as optical resonators and superconducting qubits, and exceptional points (EPs) are defective spectral singularities of such non-Hermitian operators. In contrast, the scattering-theoretic formulation of EP physics for unbounded Hamiltonians remains less settled. In this work, we formulate the geometric phase associated with encircling an EP when the underlying eigenstates are quantum resonances within a one-dimensional scattering model. To do this, we employ the complex-scaling method, where resonance poles of the S matrix are realized as discrete eigenvalues of the non-Hermitian dilated Hamiltonian, to construct situations in which resonant and scattering states coalesce into an EP in the complex energy plane, that is, the resonance pole is embedded into the continuum spectrum. We analyze the self-orthogonality in the vicinity of an EP, the Berry phase, and the Chern characteristic. Our results clarify how EP branch structure and geometric holonomy arise directly from resonance poles in scattering theory, thereby connecting non-Hermitian spectral topology with the traditional theory of quantum resonances.

quant-ph↗

arXiv2025

't Hooft line in 4D $U(1)$ lattice gauge theory and a microscopic description of dyon's statistics

In lattice gauge theory with compact gauge field variables, an introduction of the gauge field topology requires the assumption that lattice field configurations are sufficiently smooth. This assumption is referred to as the admissibility condition. However, the admissibility condition always ensures the Bianchi identity, and thus prohibits the existence of magnetic objects such as the 't~Hooft line. Recently, in 2D compact scalar field theory, Ref.~\cite{Abe:2023uan} proposed a method to define magnetic objects without violating the admissibility condition by introducing holes into the lattice. In this paper, we extend this ``excision method'' to 4D Maxwell theory and propose a new definition of the 't~Hooft line on the lattice. Using this definition, we first demonstrate a lattice counterpart of the Witten effect which endows the 't~Hooft line with electric charge and make it a dyon. Furthermore, we show that by interpreting the 't~Hooft line as a boundary of the lattice system, the statistics of the dyon can be directly read off. We also explain how the dyonic operator which satisfies the Dirac quantization condition becomes a genuine loop operator even at finite lattice spacings.

hep-lat↗

arXiv2025

Novel Lattice Formulation of 2D Chiral Gauge Theory via Bosonization

Recently, lattice formulations of 2D Abelian chiral gauge theory have been constructed based on Abelian bosonization. It is remarkable about these 2D lattice formulations that they reproduce the same gauge anomaly structure as the continuum theory, even at a finite lattice spacing. In this talk, we propose yet another lattice formulation based on the ``excision method'' introduced recently in Ref.~\cite{Abe:2023uan}. This approach respects the admissibility condition, which is a constraint on the smoothness of lattice field configurations; it usually prohibits magnetically charged objects, that is, vector-charged objects in fermion theories. We show that such objects can be defined in the excision method as a lattice defect called a ``hole,'' and discuss the selection rules for charged objects.

hep-lat↗

arXiv2024

Axion QED as a Lattice Gauge Theory and Non-Invertible Symmetry

We investigate the non-invertible symmetry associated with chiral symmetry in axion quantum electrodynamics (QED) using the modified Villain formulation. In axion QED, it is known that naive magnetic objects such as 't Hooft loops and axion strings lose their gauge invariance due to the violation of the Bianchi identity for the field strength of the photon or "field strength" of the axion. First, we construct the action of axion QED on the square lattice, which is more intricate than its counterpart in the continuum theory. We then observe the breaking of gauge invariance. Subsequently, we construct gauge-invariant magnetic objects by introducing new degrees of freedom localized at the positions of the magnetic objects. Furthermore, we explicitly compute the response of the magnetic objects under the action of the non-invertible symmetry operator constructed in Ref. [1]. In this analysis, we employ a method different from the so-called half-space gauging, which is the standard method to study non-invertible symmetries.

hep-lat↗

arXiv2024

Action of the axial $U(1)$ non-invertible symmetry on the 't~Hooft line operator: A simple argument

Employing the modified Villain lattice formulation of the axion quantum electrodynamics, we present an alternative and much simpler derivation of the conclusion of~Ref.~\cite{Honda:2024sdz} that the sweep of the axial $U(1)$ non-invertible symmetry operator over the (non-genuine) gauge invariant 't~Hooft line operator with an integer magnetic charge does not leave any effect. The point is that such a 't~Hooft line can be represented by a boundary of a (non-topological) defect that is invariant under the axial transformation on the axion field.

hep-lat↗

arXiv2024

Action of the axial $U(1)$ non-invertible symmetry on the 't~Hooft line operator: A lattice gauge theory study

We study how the symmetry operator of the axial $U(1)$ non-invertible symmetry acts on the 't~Hooft line operator in the $U(1)$ gauge theory by employing the modified Villain-type lattice formulation. We model the axial anomaly by a compact scalar boson, the ``QED axion''. For the gauge invariance, the simple 't~Hooft line operator, which is defined by a line integral of the dual $U(1)$ gauge potential, must be ``dressed'' by the scalar and $U(1)$ gauge fields. A careful consideration on the basis of the anomalous Ward--Takahashi identity containing the 't~Hooft operator with the dressing factor and a precise definition of the symmetry operator on the lattice shows that the symmetry operator leaves no effect when it sweeps out a 't~Hooft loop operator. This result appears inequivalent with the phenomenon concluded in the continuum theory. In an appendix, we demonstrate that the half-space gauging of the magnetic $\mathbb{Z}_N$ 1-form symmetry, when formulated in an appropriate lattice framework, leads to the same conclusion as above. A similar result is obtained for the axion string operator.

hep-lat↗

arXiv2024

Yet another lattice formulation of 2D $U(1)$ chiral gauge theory via bosonization

Recently, lattice formulations of Abelian chiral gauge theory in two dimensions have been devised on the basis of the Abelian bosonization. A salient feature of these 2D lattice formulations is that the gauge invariance is \emph{exactly\/} preserved for anomaly-free theories and thus is completely free from the question of the gauge mode decoupling. In the present paper, we propose a yet another lattice formulation sharing this desired property. A particularly unique point in our formulation is that the vertex operator of the dual scalar field, which carries the vector charge of the fermion and the ``magnetic charge'' in the bosonization, is represented by a ``hole'' excised from the lattice; this is the excision method formulated recently by Abe et al. in a somewhat different context.

hep-lat↗

arXiv2024

Lattice realization of the axial $U(1)$ noninvertible symmetry

In $U(1)$ lattice gauge theory with compact $U(1)$ variables, we construct the symmetry operator, i.e.\ the topological defect, for the axial $U(1)$ noninvertible symmetry. This requires a lattice formulation of chiral gauge theory with an anomalous matter content and we employ the lattice formulation on the basis of the Ginsparg--Wilson relation. The invariance of the symmetry operator under the gauge transformation of the gauge field on the defect is realized, imitating the prescription by Karasik in continuum theory, by integrating the lattice Chern--Simons term on the defect over \emph{smooth\/} lattice gauge transformations. The projection operator for allowed magnetic fluxes on the defect then emerges with lattice regularization. The resulting symmetry operator is manifestly invariant under lattice gauge transformations. In an appendix, we give another way of constructing the symmetry operator on the basis of a 3D $\mathbb{Z}_N$ topological quantum field theory, the level-$N$ BF theory on the lattice.

hep-lat↗

arXiv2023

Lattice construction of mixed 't Hooft anomaly with higher-form symmetry

In this talk, we give the lattice regularized formulation of the mixed 't Hooft anomaly between the $\mathbb{Z}_N$ $1$-form symmetry and the $θ$ periodicity for $4$d pure Yang-Mills theory, which was originally discussed by Gaiotto $\textit{et al.}$ in the continuum description. For this purpose, we define the topological charge of the lattice $SU(N)$ gauge theory coupled with the background $\mathbb{Z}_N$ $2$-form gauge fields $B_p$ by generalizing Lüscher's construction of the $SU(N)$ topological charge. We show that this lattice topological charge enjoys the fractional $1/N$ shift completely characterized by the background gauge field $B_p$, and this rigorously proves the mixed 't Hooft anomaly with the finite lattice spacings. As a consequence, the Yang-Mills vacua at $θ$ and $θ+2π$ are distinct as the symmetry-protected topological states when the confinement is assumed.

hep-lat↗

arXiv2023

Higher-group symmetry in lattice gauge theories with restricted topological sectors

In this paper, we give a brief overview of generalized symmetries from the point of view of the lattice regularization as a fully regularized framework. At first, we illustrate the generalization of 't~Hooft anomaly matching for higher-form symmetries. Furthermore the main interest goes to the higher-group symmetry. In particular, we find that the so-called $4$-group appears in the lattice Yang--Mills theory under modification of instanton sum.

hep-lat↗

arXiv2023

Note on lattice description of generalized symmetries in $SU(N)/\mathbb{Z}_N$ gauge theories

Topology and generalized symmetries in the $SU(N)/\mathbb{Z}_N$ gauge theory are considered in the continuum and the lattice. Starting from the $SU(N)$ gauge theory with the 't~Hooft twisted boundary condition, we give a simpler explanation of the van~Baal's proof on the fractionality of the topological charge. This description is applicable to both continuum and lattice by using the generalized Lüscher's construction of topology on the lattice. Thus we can recover the $SU(N)/\mathbb{Z}_N$ principal bundle from lattice $SU(N)$ gauge fields being subject to the $\mathbb{Z}_N$-relaxed cocycle condition. We explicitly demonstrate the fractional topological charge, and verify an equivalence with other constructions reported recently based on different ideas. Gauging the $\mathbb{Z}_N$ $1$-form center symmetry enables lattice gauge theories to couple with the $\mathbb{Z}_N$ $2$-form gauge field as a simple lattice integer field, and to reproduce the Kapustin--Seiberg prescription in the continuum limit. Our construction is also applied to analyzing the higher-group structure in the $SU(N)$ gauge theory with the instanton-sum modification.

hep-th↗

arXiv2023

Magnetic operators in 2D compact scalar field theories on the lattice

In lattice compact gauge theories, we must impose the admissibility condition to have well-defined topological sectors. The admissibility condition, however, usually forbids the presence of magnetic operators, and it is not so trivial if one can study the monopole physics depending on the topological term, such as the Witten effect, on the lattice. In this paper, we address this question in the case of 2D compact scalars as it would be one of the simplest examples having analogues of the monopole and the topological term. To define the magnetic operator, we propose the ``excision method,'' which consists of excising lattice links (or bonds) in an appropriate region containing the monopole and defining the dual lattice in a particular way. The size of the excised region is $O(1)$ in lattice units so that the monopole becomes point-like in the continuum limit. We give the lattice derivation of the 't~Hooft anomalies between the electric and magnetic symmetries and also derive the higher-group-like structure related to the Witten effect.

hep-lat↗

arXiv2023

Topology of $SU(N)$ lattice gauge theories coupled with $\mathbb{Z}_N$ $2$-form gauge fields

We extend the definition of Lüscher's lattice topological charge to the case of $4$d $SU(N)$ gauge fields coupled with $\mathbb{Z}_N$ $2$-form gauge fields. This result is achieved while maintaining the locality, the $SU(N)$ gauge invariance, and $\mathbb{Z}_N$ $1$-form gauge invariance, and we find that the manifest $1$-form gauge invariance plays the central role in our construction. This result gives the lattice regularized derivation of the mixed 't Hooft anomaly in pure $SU(N)$ Yang-Mills theory between its $\mathbb{Z}_N$ $1$-form symmetry and the $θ$ periodicity.

hep-lat↗