Yoshio Kikukawa

• Professor at The University of Tokyo

We study the lattice Schwinger model by combining the variational uniform matrix product state (VUMPS) algorithm with a gauge-invariant matrix product ansatz that locally enforces the Gauss law constraint. Both the continuum and lattice versions of the Schwinger model with θ = π are known to exhibit first-order phase transitions for the values of t...

We study the lattice Schwinger model by combining the variational uniform matrix product state (VUMPS) algorithm with a gauge-invariant matrix product ansatz that locally enforces the Gauss law constraint. Both the continuum and lattice versions of the Schwinger model with $\theta=\pi$ are known to exhibit first-order phase transitions for the valu...

A bstract We examine the proposal by Grabowska and Kaplan (GK) to use the infinite gradient flow in the domain-wall formulation of chiral lattice gauge theories. We consider the case of Abelian theories in detail, for which Lüscher’s exact gauge-invariant formulation is known, and we relate GK’s formulation to Lüscher’s one. The gradient flow can b...

We examine the proposal by Grabowska and Kaplan (GK) to use the infinite gradient flow in the domain-wall formulation of chiral lattice gauge theories. We consider the case of Abelian theories in detail, for which L\"uscher's exact gauge-invariant formulation is known, and we relate GK's formulation to L\"uscher's one. The gradient flow can be form...

We consider the lattice formulation of SO(10) chiral gauge theory with left-handed Weyl fermions in the sixteen dimensional spinor representation ($\underline{16}$) within the framework of the Overlap fermion/the Ginsparg-Wilson relation. We define a manifestly gauge-invariant path-integral measure for the left-handed Weyl field using the whole com...

We consider the lattice formulation of SO(10) chiral gauge theory with left-handed Weyl fermions in the sixteen dimensional spinor representation ($\underline{16}$) within the framework of the Overlap fermion/the Ginsparg-Wilson relation. We define a manifestly gauge-invariant path-integral measure for the left-handed Weyl field using all the compo...

In the mirror fermion approach with Ginsparg-Wilson fermions, it has been argued that the mirror fermions do not decouple: in the 345 model with Dirac- and Majorana-Yukawa couplings to XY-spin field, the two-point vertex function of the (external) gauge field in the mirror sector shows a singular non-local behavior in the PMS phase. We re-examine w...

In the mirror fermion approach with Ginsparg-Wilson fermions, it has been argued that the mirror fermions do not decouple: in the 345 model with Dirac- and Majorana-Yukawa couplings to XY-spin field, the two-point vertex function of the (external) gauge field in the mirror sector shows a singular non-local behavior in the PMS phase. We re-examine w...

Statistical sampling with the complex Langevin (CL) equation is applied to (0+1)-dimensional Thirring model, and its uniform-field variant, at finite fermion chemical potential $\mu$. The CL simulation reproduces a crossover behavior which is similar to but actually deviating from the exact solution in the transition region, where we confirm that t...

Based on the Lefschetz thimble formulation of path-integration, we analyze the (0+1) dimensional Thirring model at finite chemical potentials and perform hybrid Monte Carlo (HMC) simulations. We adopt the lattice action defined with the staggered fermion and a compact link field for the auxiliary vector field. We firstly locate the critical points...

We consider the one-dimensional massive Thirring model formulated on the lattice with staggered fermions and an auxiliary compact vector (link) field, which is exactly solvable and shows a phase transition with increasing the chemical potential of fermion number: the crossover at a finite temperature and the first order transition at zero temperatu...

We investigate Lefschetz thimble structure of the complexified path-integration in the one-dimensional lattice massive Thirring model with finite chemical potential. The lattice model is formulated with staggered fermions and a compact auxiliary vector boson (a link field), and the whole set of the critical points (the complex saddle points) are so...

We numerically study the SU(2) gauge theory with two dynamical flavors of the domain-wall fermions in fundamental representation. The meson spectra and the residual mass are measured on three lattice volumes and at two values of gauge coupling so as to investigate the finite volume effect. On generated configurations, eigenvalues of the overlap fer...

We consider a hybrid Monte Carlo algorithm which is applicable to lattice theories defined on Lefschetz thimbles. In the algorithm, any point (field configuration) on a thimble is parametrized uniquely by the flow-direction and the flow-time defined at a certain asymptotic region close to the critical point, and it is generated by solving the gradi...

The property of charged fermion states is investigated in the quenched U(1) chiral Wilson–Yukawa model. Fitting the charged fermion propagator with a single hyperbolic cosine does not yield reliable results. On the other hand the behavior of the propagator including large lattice size dependence is well described by the large Wilson–Yukawa coupling...

We correct the incomplete proof of the global integrability condition for non-gauge loops (the non-contractible loops along the Wilson-line degrees of freedom of U(1) gauge field) in JHEP05(2008)095. Accordingly, the reconstruction theorem is reformulated. The main result does not change.

By using overlap Majorana fermions, the ${\cal N}=1$ chiral multiple can be formulated so that the supersymmetry is manifest and the vacuum energy is cancelled in the free limit, thanks to the bilinear nature of the free action. It is pointed out, however, that in this formulation the reflection positivity is violated in the bosonic part of the act...

It is shown that free lattice Dirac fermions defined by overlap Dirac operator fulfill the Osterwalder-Schrader reflection positivity condition with respect to the link-reflection. Comment: 7 pages, presented at the XXVIII International Symposium on Lattice Field Theory, Lattice 2010, title slightly modified. v2 minor corrections

We discuss on a lattice formulation of 2D N = (2,2) SQCD preserving one of its supercharges. In particular, the overlap Dirac operator, which satisfies the Ginsparg‐Wilson relation, is introduced to the matter sector of the theory. It exactly realizes chiral flavor symmetry on lattice, to make possible to define the lattice action for general numbe...

It has been conjectured that the two-dimensional N=2 Wess-Zumino model with a quasi-homogeneous superpotential provides the Landau-Ginzburg description of the N=2 superconformal minimal models. For the cubic superpotential W=(lambda) Phi^3/3, it is expected that the Wess-Zumino model describes A_{2} model and the chiral superfield Phi shows the con...

It is shown that free lattice fermions defined by overlap Dirac operator fulfill the Osterwalder-Schrader reflection positivity condition with respect to the link-reflection. The proof holds true in non-gauge models with interactions such as chiral Yukawa models. Comment: 16pages, the proof for Weyl fermions and chiral Yukawa model are explained in...

The two-dimensional N = 2 Wess-Zumino model with a quasi-homogeneous superpotential is believed to provide a Landau-Ginzburg description of the two-dimensional N = 2 superconfor-mal minimal model. For the cubic superpotential W = λ Φ 3 /3, it is expected that the Wess-Zumino model describes A 2 model and the chiral superfield Φ shows the conformal...

In models of dynamical electroweak symmetry breaking due to strongly coupled fourth-family quarks and leptons, their low-energy effective descriptions may involve multiple composite Higgs fields, leading to a possibility that the electroweak phase transition at finite temperature is first order due to the Coleman-Weinberg mechanism. We examine the...

It has been argued by Pisarski and Wilczek that finite temperature restoration of SU(N{sub f})xSU(N{sub f}) chiral symmetry is first order for N{sub f}{>=}3. This type of chiral symmetry with large N{sub f} may appear in the Higgs sector if one considers models such as walking technicolor theories. We examine the first-order restoration of chiral s...

We calculate electromagnetic mass differences by lattice simulations. Electro-magnetic and isospin breaking contribution to light hadrons are estimated. Violation of Dashen's theorem as well as proton-neutron mass difference are obtained. We also extract quark masses from the spectrum and examined QED corrections to them.

We present a gauge-invariant lattice formulation of the Glashow-Weinberg-Salam model based on the lattice Dirac operator satisfying the Ginsparg-Wilson relation. Our construction covers all topologically non-trivial SU(2) sectors with vanishing U(1) magnetic ux and would be usable for a descrip-tion of the baryon number non-conservation.

We present a gauge-invariant and non-perturbative construction of the Glashow-Weinberg-Salam model on the lattice, based on the lattice Dirac operator satisfying the Ginsparg-Wilson relation. Our construction covers all SU(2) topological sectors with vanishing U(1) magnetic flux and would be usable for a description of the baryon number non-conse...

In the gauge invariant formulation of U(1) chiral lattice gauge theories based on the Ginsparg-Wilson relation, the gauge field dependence of the fermion measure is determined through the so-called measure term. We derive a closed formula of the measure term on the finite volume lattice. The Wilson line degrees of freedom (torons) of the link fie...

In continuum field theory, it has been discussed that chiral gauge theories with Weyl fermions in anomalous gauge representations (anomalous gauge theories) can consistently be quantized, provided that some of gauge bosons are permitted to acquire mass. Such theories in four dimensions are inevitablly non-renormalizable and must be regarded as a lo...

We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can be calculated in lattice QCD simulations in the presence of the CP violating $\theta$ term. In this paper we measure the energy difference between spin-up and spin-down states of the neutron in the presence of an uniform and static external electric field. We first test thi...

We carry out a feasibility study toward a lattice QCD calculation of the neutron electric dipole moment (NEDM) in the presence of the $\theta$ term using two different approaches. In the first method, we calculate the CP-odd electromagnetic form factor $F_3$, which becomes the NEDM in the zero momentum transfer limit. At the first order in $\theta$...

We calculate electromagnetic mass difference of mesons using a method proposed by Duncan {\it et al}. The RG-improved gauge action and the non-compact Abelian gauge action are employed to generate configurations. Quark propagators in the range of $m_{PS}/m_{V}=0.76-0.51$ are obtained with the meanfield-improved clover quark action. Chiral and conti...

We carry out a feasibility study for the lattice QCD calculation of the neutron electric dipole moment (NEDM) in the presence of the $\theta$ term. We develop the strategy to obtain the nucleon EDM from the CP-odd electromagnetic form factor $F_3$ at small $\theta$, in which NEDM is given by $\lim_{q^2\to 0}\theta F_3(q^2)/(2m_N)$ where $q$ is the...

A new technique is proposed to classify a topological field in abelian lattice gauge theories. We perform the classification by regarding the topological field as a local composite field of the gauge field tensor instead of the vector potential associated to an admissible gauge field. Our method reproduces the result obtained by the ordinary method...

A lattice Wess-Zumino model is formulated on the basis of Ginsparg-Wilson fermions. In perturbation theory, our formulation is equivalent to the formulation by Fujikawa and Ishibashi and by Fujikawa. Our formulation is, however, free from a singular nature of the latter formulation due to an additional auxiliary chiral supermultiplet on a lattice....

We consider a numerical method to solve the local cohomology problem related to the gauge anomaly cancellation in U(1) chiral gauge theories. In the cohomological analysis of the chiral anomaly, it is required to carry out the differentiation and the integration of the anomaly with respect to the continuous parameter for the interpolation of the ad...

The axial anomaly arising from the fermion sector of U(N) or SU(N) reduced model is studied under a certain restriction of gauge field configurations (the ``U(1) embedding'' with N = Ld). We use the overlap-Dirac operator and consider how the anomaly changes as a function of a gauge-group representation of the fermion. A simple argument shows that...

In the gauge-invariant construction of abelian chiral gauge theories on the lattice based on the Ginsparg-Wilson relation, the gauge anomaly is topological and its cohomologically trivial part plays the role of the local counter term. We give a prescription to solve the local cohomology problem within a finite lattice by reformulating the Poincar\'...

We consider abelian chiral gauge theories on the lattice with exact gauge invariance in which the admissible gauge fields are restricted to the ZN subgroup of the original U(1). In the gauge-invariant construction of the original U(1) theory, the gauge anomaly is topological and its cohomologically trivial part plays the role of the local counter t...

The axial anomaly arising from the fermion sector of $\U(N)$ or $\SU(N)$ reduced model is studied under a certain restriction of gauge field configurations (the ``$\U(1)$ embedding'' with $N=L^d$). We use the overlap-Dirac operator and consider how the anomaly changes as a function of a gauge-group representation of the fermion. A simple argument s...

Two-dimensional N=2 Wess-Zumino model is constructed on the lattice through Nicolai mapping with Ginsparg-Wilson fermion. The Nicolai mapping requires a certain would-be surface term in the bosonic action which ensures the vacuum energy cancellation even on the lattice, but inevitably breaks chiral symmetry. With the Ginsparg-Wilson fermion, the ho...

Two-dimensional N=2 Wess-Zumino model is constructed on the lattice through Nicolai mapping with Ginsparg-Wilson fermion. The Nicolai mapping requires a certain would-be surface term in the bosonic action which ensures the vacuum energy cancellation even on the lattice, but inevitably breaks chiral symmetry. With the Ginsparg-Wilson fermion, the ho...

On the basis of an observation due to Kiskis, Narayanan and Neuberger, we show that there is a remnant of chiral anomalies in the reduced model when a Dirac operator which obeys the Ginsparg-Wilson relation is employed for the fermion sector. We consider fermions belonging to the fundamental representation of the gauge group U(N) or SU(N). For vect...

Theoretical issues of exact chiral symmetry on the lattice are discussed and related recent works are reviewed. For chiral theories, the construction with exact gauge invariance is reconsidered from the point of view of domain wall fermion. The issue in the construction of electroweak theory is also discussed. For vector-like theories, we discuss u...

Based on the Ginsparg-Wilson relation, a gauge invariant formulation of electroweak SU(2) × U(1) gauge theory on the lattice is considered. If the hypercharge gauge coupling is turned off in the vacuum sector of the U(1) gauge fields, the theory consists of four left-handed SU(2) doublets and it is possible, as in vector-like theories, to make the...

Based on the Ginsparg-Wilson relation, a gauge invariant formulation of electroweak SU(2)xU(1) gauge theory on the lattice is considered. If the hypercharge gauge coupling is turned off in the vacuum sector of the U(1) gauge fields, the theory consists of four left-handed SU(2) doublets and it is possible, as in vector-like theories, to make the fe...

We discuss how to construct anomaly-free chiral gauge theories on the lattice with exact gauge invariance in the framework of domain wall fermion. Chiral gauge coupling is realized by introducing a five-dimensional gauge field which interpolates between two different four-dimensional gauge fields at boundaries. The five-dimensional dependence is co...

We discuss how to construct anomaly-free chiral gauge theories on the lattice with exact gauge invariance in the framework of domain wall fermion. Chiral gauge coupling is realized by introducing a five-dimensional gauge field which interpolates between two different four-dimensional gauge fields at boundaries. The five-dimensional dependence is co...

Chiral symmetry and locality property of low energy effective action of domain-wall fermion are discussed.

We consider the cohomological classification of the (4+2)-dimensional topological field which was proposed by Lüscher, for the SU(2) U(1) electroweak theory. The dependence on the admissible abelian gauge field of U(1) is determined through topological argument, with the SU(2) gauge field fixed as background. We then show the exact cancellation of...

We discuss locality in the domain-wall QCD through the effective four-dimensional Dirac operator which is defined by the transfer matrix of the five-dimensional Wilson fermion. We first derive an integral representation for the effective operator, using the inverse five-dimensional Wilson–Dirac operator with the anti-periodic boundary condition in...

We consider a lattice implementation of the eta-invariant, using the complex phase of the determinant of the simplified domain-wall fermion which couples to an interpolating five-dimensional gauge field. We clarify the relation to the effective action for chiral Ginsparg-Wilson fermions. A lattice expression for the five-dimensional Chern-Simons te...

We consider the cohomological classification of the 4+2-dimensional topological field, which is proposed by L\"uscher, for SU(2)_L \times U(1)_Y electroweak theory. The dependence on the admissible abelian gauge field of U(1)_Y is determined through topological argument, with SU(2)_L gauge field fixed as background. We then show the exact cancellat...

We discuss locality in the domain-wall QCD through the effective four-dimensional Dirac operator which is defined by the transfer matrix of the five-dimensional Wilson fermion. We first derive an integral representation for the effective operator, using the inverse five-dimensional Wilson-Dirac operator with the anti-periodic boundary condition in...

We discuss the weak coupling expansion of lattice QCD with the overlap Dirac operator. The Feynman rules for lattice QCD with the overlap Dirac operator are derived and the quark self-energy and vacuum polarization are studied at the one-loop level. We confirm that their divergent parts agree with those in the continuum theory.

We derive the effective action of the light fermion field of the domain-wall fermion, which is referred as $q(x)$ by Furman and Shamir. The inverse of the effective Dirac operator turns out to be identical to the inverse of the truncated overlap Dirac operator, except a local contact term which would give the chiral symmetry breaking in the Ginspar...

We consider a lattice implementation of the eta-invariant, using the complex phase of the determinant of the simplified domain-wall fermion, which couples to an interpolating five-dimensional gauge field. We clarify the relation to the effective action for chiral Ginsparg-Wilson fermions. The integrability, which holds true for anomaly-free theorie...

We consider the exact chiral symmetry and its spontaneous breakdown in lattice QCD with the Dirac operators satisfying the Ginsparg-Wilson relation. The axial vector current, which turns out to be related to the vector current simply by the insertion of the operator γ5 (1 − aD), is explicitly constructed in the cases of the Neuberger-Dirac operator...

Using the grassman-number-integral representation of the vacuum overlap formula, it is shown that the symmetry of the auxiliary quantum fermion system in the overlap formalism induces exact chiral symmetry of the action of the type given by Luscher under the chiral transformation $\delta \psi_n = \gamma_5(1-a D)\psi_n$ and $ \delta \bar \psi_n = \b...

Three aspects of the symmetry structure of lattice chiral fermions in the overlap formalism are discussed. By the weak coupling expansion of the overlap Dirac operator, the axial anomaly associated to the chiral transformation proposed by Lüscher is evaluated and is shown to have the correct form of the topological charge density for perturbative b...

Three aspects of symmetry structure of lattice chiral fermion in the overlap formalism are discussed. By the weak coupling expansion of the overlap Dirac operator, the axial anomaly associated to the chiral transformation proposed by Luescher is evaluated and is shown to have the correct form of the topological charge density for perturbative backg...

We discuss the exact chiral symmetry and its spontaneous breakdown in lattice QCD with the Dirac operators satisfying the Ginsparg-Wilson relation. The axial vector current, which turns out to be related to the vector current simply by the insertion of the operator \gamma_5 (1-aD), is explicitly constructed in the case of the Neuberger-Dirac operat...

We discuss the weak coupling expansion of massless QCD with the Dirac operator which is derived by Neuberger based on the overlap formalism and satisfies the Ginsparg-Wilson relation. The axial U(1) anomaly associated to the chiral transformation proposed by Lüscher is calculated as an application and is shown to have the correct form of the topolo...

A certain U(1) model in 2 dimensions, describing four right handed unit charged Weyl fermions interacting with one doubly charged left handed Weyl fermion, is exactly soluble and has massless Majorana-Weyl composites. Instanton induced fermion number violation is essential for 't Hooft anomaly consistency. The associated 't Hooft vertex can be anal...

Dynamical nature of the gauge degrees of freedom and its effect to fermion spectrum are studied at β = ∞ for two- and four-dimensional nonabelian chiral gauge theories in the vacuum overlap formalism. It is argued that the disordered gauge degrees of freedom does not contradict to the chiral spectrum of lattice fermion.

The vacuum overlap formalism is extended to describe the supersymmetric multiplet of a Weyl fermion, a complex scalar boson and an auxiliary field in the case without interaction, based on the fact that supersymmetry can be maintained upto quadratic terms by introducing bosonic species doublers. We also obtain a local action which describes the chi...

A certain truncation of the overlap (domain wall fermions) contains k flavors of Wilson-Dirac fermions. We show that for sufficiently weak lattice gauge fields the effective mass of the lightest Dirac particle is exponentially suppressed in k. This suppression is seen to disappear when lattice topology is non-trivial. We check explicitly that the s...

A certain U(1) model in 2 dimensions, describing four right handed unit charged Weyl fermions interacting with one doubly charged left handed Weyl fermion, is exactly soluble and has massless Majorana-Weyl composites. Instanton induced fermion number violation is essential for 't Hooft anomaly consistency. The associated 't Hooft vertex can be anal...

Dynamical nature of the gauge degrees of freedom and its effect to fermion spectrum are studied at $\beta=\infty$ for two- and four-dimensional nonabelian chiral gauge theories in the vacuum overlap formalism. It is argued that the disordered gauge degrees of freedom does not contradict to the chiral spectrum of lattice fermion.

Dynamical nature of the gauge degree of freedom and its effect to fermion spectrum are studied for four-dimensional nonabelian chiral gauge theory in the vacuum overlap formulation. The covariant gauge fixing term and the Faddeev-Popov determinant are introduced by hand as a weight for the gauge average. At $\beta=\infty$, as noticed by Hata some t...

In odd dimensions the lattice overlap formalism is simpler than in even dimensions. Masslessness of fermions can still be preserved without fine tuning and gauge invariance without gauge averaging can be maintained, although, sometimes, only at the expense of parity invariance. When parity invariance is enforced invariance under small gauge transfo...

Dynamical nature of the gauge degree of freedom and its effect to fermion spectrum are studied at $\beta=\infty$ for two-dimensional nonabelian chiral gauge theory in the vacuum overlap formulation. It is argue that the disordered gauge degree of freedom does not necessarily cause the massless chiral state in the (waveguide) boundary correlation fu...

We describe in some detail a computer evaluation of a 't Hooft vertex in a two dimensional model using the overlap. The computer result agrees with the known exact continuum value, and in this sense our work is a first successful fully dynamical simulation of a chiral gauge theory on the lattice. We add some new data to numbers obtained earlier and...

An argument is presented for a certain universality of finite size corrections in two dimensional gauge theories. In the abelian case a direct calculation is carried out for a particular chiral model. The analytical result confirms the above universality and that the 't Hooft vertex previously measured using the overlap smoothly approaches the corr...

We calculate the complex phase of chiral determinant by the vacuum overlap formula with configurations of two-dimensional U(1) gauge field fixed in Landau and Laplacian gauge. The complex phase fluctuates over the Gribov copies, which appear in the process of Landau gauge fixing and contain vortex-like singularities. In the Laplacian gauge, the flu...

We examine the vacuum overlap formula for the two-dimensional SU(2) Wess-Zumino term in lattice regularization. Perturbatively, this formula reproduces the Wess-Zumino term correctly in the continuum limit and yields the IR fixed point in the beta function of the chiral model. Nonperturbatively it shows a sharp Gaussian distribution for the SU(2) c...

Taking into account of the boundary condition in the fifth direction which is derived from the lattice Wilson fermion, we develop a theory of five-dimensional fermion with kink-like and homogeneous masses in finite extent of the fifth dimension. The boundary state wave functions are constructed explicitly and the would-be vacuum overlap is expanded...

Being inspired by Kaplan’s proposal for simulating chiral fermions on a lattice, we examine the continuum analogue of his domain-wall construction for two-dimensional chiral Schwinger models. Adopting a slightly unusual dimensional regularization, we explicitly evaluate the one-loop effective action in the limit that the domain-wall mass goes to in...

The fermionic part of the Schr\"odinger functional of QCD is formulated in the lattice regularization with the staggered fermion. The boundary condition imposed on the staggered fermion field are examined in terms of the four-component Dirac spinor. The boundary terms are different from those of the Symanzik's theory in the flavor structure due to...

In the leading order of a modified 1/NC expansion, we show that a class of gauge-Higgs-Yukawa systems in four dimensions give non-trivial and well-defined theories in the continuum limit. The renormalized Yukawa coupling y and the quartic scalar coupling λ have to lie on a certain line in the (y, λ) plane and the line terminates at an upper bound....

The subtraction of massive modes and the summation over contributions of ininitely many fermions, as discussed by Narayanan and Neuberger, can make manifest not only anomaly of the chiral zero mode but also its dynamics of chiral symmetry breaking. As a result, it is possible to reproduce the “η” mass in two-dimensional CPn−1 model with quarks. The...

The subtraction of massive modes and the summation over contributions of infinitely many fermions, as discussed by Narayanan and Neuberger, can make manifest not only anomaly of the chiral zero mode but also its dynamics of chiral symmetry breaking. As a result, it is possible to reproduce the ''eta''' mass in two-dimensional CP(n-1) model with qua...

Being inspired by Kaplan's proposal for simulating chiral fermions on a lattice, we examine the continuum analog of his domain-wall construction for two-dimensional chiral Schwinger models. Adopting slightly unusual dimensional regularization, we explicitly evaluate the one-loop effective action in the limit that the domain-wall mass goes to infini...

Abelian anomaly is examined by means of the recently proposed gauge invariant regularization for SO(10) chiral gauge theory and its generalization for a theory of arbitrary gauge group with anomaly-free chiral fermion contents. For both cases it is shown that the anomaly with correct normalization can be obtained in a gauge invariant form without a...