arXiv subjects

Jun-ichi Noaki

Publications and source records attributed to Jun-ichi Noaki.

6 recordsLinked to original sources

arXiv2015

On the axial $U(1)$ symmetry at finite temperature

We study the $U(1)_A$ anomaly in two-flavor lattice QCD at finite temperature with the Möbius domain-wall Dirac operator. We generate gauge configurations in the temperature range $(0.9, 1.2) T_c$ on different physical volumes, $L=$ 2--4 fm, and lattice spacings. We measure the difference of the susceptibilities of the flavor non-singlet scalar ($χ_δ$) and pseudoscalar ($χ_π$) mesons. They are related by an axial $U(1)$ transformation and the difference vanishes if the axial $U(1)$ symmetry is respected. We identify the source of axial $U(1)$ symmetry breaking at finite temperature in the lowest eigenmodes, for the observable $χ_π- χ_δ$. We then reweight the Möbius domain-wall fermion partition function to that of the overlap-Dirac operator to fully recover chiral symmetry. Our data show a significant discrepancy in the results coming from the Möbius domain-wall valence quarks, the overlap valence quarks on our DWF configurations and the reweighted ones that have full chiral symmetry. After recovering full chiral symmetry we conclude that the difference $χ_π- χ_δ$ shows a suppression in the chiral limit that is compatible with an effective restoration of $U(1)_A$ at $T \gtrsim T_c$ in the scalar meson channels.

hep-lat↗

arXiv2014

Axial U(1) symmetry at finite temperature with Möbius domain-wall fermions

We investigate the axial $U(1)$ symmetry restoration at finite temperature in two flavor QCD. We employ the Möbius domain-wall formalism that is designed to achieve good chiral symmetry. We show the measurements of a difference of meson susceptibilities, sensitive to the $U(1)_A$ symmetry breaking. The signal is dominated by zero and near-zero modes. By reweighting the measure to that of overlap fermions we find a suppression of the $U(1)_A$ breaking effects above the chiral transition temperature.

hep-lat↗

arXiv2012

The neutral pion decay and the chiral anomaly on the lattice

We perform a lattice QCD calculation of the π^0\toγγtransition form factor and the associated decay width. We use a Euclidean time integral of the relevant three-point function to compute the decay amplitude for two-photon final state, which is a non-QCD state. We use the all-to-all quark propagator technique to carry out this integral as well as to include the disconnected quark diagram contributions. We execute the calculation using the overlap fermion formulation, which ensures the exact chiral symmetry on the lattice and produces the chiral anomaly through the Jacobian of the chiral transformation. We examine various sources of systematic effects except for possible discretization effect. Our final results for the form factor and the decay width reproduce the ABJ anomaly in the chiral limit and agree with the experimental measurements at the physical pion mass with a precision of a few percent.

hep-lat↗

arXiv2012

Two-photon decay of the neutral pion in lattice QCD

We perform non-perturbative calculation of the π^0 to γγ transition form factor and the associated decay width using lattice QCD. The amplitude for two-photon final state, which is not an eigenstate of QCD, is extracted through an Euclidean time integral of the relevant three-point function. We utilize the all-to-all quark propagator technique to carry out this integral as well as to include the disconnected quark diagram contributions. The overlap fermion formulation is employed on the lattice to ensure exact chiral symmetry on the lattice. After examining various sources of systematic effects except for possible discretization effect, we obtain Γ=7.83(31)(49) eV for the pion decay width, where the first error is statistical and the second is our estimate of the systematic error.

hep-lat↗

arXiv2012

Topological susceptibility and axial symmetry at finite temperature

We consider the simulation of finite temperature QCD with two flavors of dynamical overlap fermions in order to study the suppression of the axial U(1) symmetry breaking at the chiral phase transition point. As a preliminary study, pure gauge simulations are performed to investigate how fixing the topology affects physical quantities like the topological susceptibility, $χ_t$, at finite temperature, showing that it is possible to reconstruct known results from the fixed topology sector. First results on the degeneracy of meson correlators in the high temperature QGP sector are shown.

hep-lat↗

arXiv2010

Finite temperature QCD at fixed Q with overlap fermions

We present some preliminary results of the project on finite temperature QCD with overlap fermions at KEK. We performed a series of simulations to assess the effects of fixing the topological sector at finite temperature and we will show the first calculations of topological susceptibility and meson masses for quenched and full QCD.

hep-lat↗