arXiv subjects

Arata Yamamoto

Publications and source records attributed to Arata Yamamoto.

69 records · Page 4Linked to original sources

arXiv2011

Chiral magnetic effect in lattice QCD with a chiral chemical potential

We perform a first lattice QCD simulation including two-flavor dynamical fermion with a chiral chemical potential. Because the chiral chemical potential gives rise to no sign problem, we can exactly analyze a chirally imbalanced QCD matter by the Monte Carlo simulation. By applying an external magnetic field to this system, we obtain a finite induced current along the magnetic field, which corresponds to the chiral magnetic effect. The obtained induced current is proportional to the magnetic field and to the chiral chemical potential, which is consistent with an analytical prediction.

hep-lat↗

arXiv2011

Lattice QCD Anatomy via the Energy-Momentum Component of Gluons

In this thesis, we perform the lattice QCD analysis via the energy-momentum component of gluons. By introducing the momentum cutoff to the link variable, we investigate which energy-momentum components of gluons induce each QCD phenomenon. We use the Landau gauge for the most part of the lattice QCD analysis. In lattice QCD, we analyze color confinement, spontaneous chiral symmetry breaking, topological charge, and the related topics. We also discuss several comparisons with effective theories. As for color confinement, we calculate the quark-antiquark potential, the color flux tube, and meson masses. From quantitative analysis, we find that color confinement is induced by the low-momentum component below 1.5 GeV. As for spontaneous chiral symmetry breaking, we calculate the chiral condensate and the Dirac spectrum. Spontaneous chiral symmetry breaking is induced by the broad low-momentum component which ranges even above 1.5 GeV. The present result suggests that color confinement and spontaneous chiral symmetry breaking are induced by somehow different energy-momentum components of gluons. As for topological charge, we calculate the topological charge density and the Dirac zero mode. Topological charge is induced by the broad energy-momentum component, which is similar to spontaneous chiral symmetry breaking.

hep-lat↗

arXiv2011

Four-dimensional Yang-Mills theory with a three-dimensional fermion membrane

We study the four-dimensional Yang-Mills theory in the presence of a three-dimensional membrane of fermions by lattice Monte Carlo simulations. We analyze the phase structure of this theory at finite temperature. Below the phase transition temperature of the pure Yang-Mills theory, we obtain an unconventional phase with spatially-nonuniform vacuum. In this phase, the expectation value of the Polyakov loop is finite on the membrane, and it exponentially decays to zero outside the membrane.

hep-lat↗

arXiv2010

Lattice QCD Study for Gluon Propagator and Gluon Spectral Function

We study the gluon propagator in the Landau gauge in SU(3) lattice QCD at $β$=5.7, 5.8 and 6.0 at the quenched level. The Euclidean Landau-gauge gluon propagator $D(r)\equiv D_{μμ}^{aa}(x)/24$ is found to be well described by four-dimensional Yukawa-type function $e^{-mr}/r$ in the infrared and intermediate region of $r \equiv (x_μx_μ)^{1/2}$ = 0.1 $\sim$ 1.0fm. The infrared effective gluon mass is obtained as $m \simeq$ 600MeV. Associated with the 4D Yukawa-type gluon propagator, we derive analytical expressions for the zero-spatial-momentum propagator $D_0(t)$, the effective mass $M_{\rm eff}(t)$, and the spectral function $ρ(ω)$ of the gluon field. Remarkably, the obtained gluon spectral function $ρ(ω)$ is almost negative definite, except for a positive $δ$-functional peak at $ω=m$. Since the Yukawa-type propagation indicates a three-dimensional space-time character, we consider a hypothesis of an effective dimensional reduction by generalized Parisi-Sourlas mechanism in a stochastic color-magnetic vacuum of infrared QCD.

hep-lat↗

arXiv2010

QCD Dirac spectrum and components of the gauge field

We analyze the relation between the Dirac spectrum and the gauge field in SU(3) lattice QCD. We focus on how components of the gauge field are related to the Dirac spectrum. First, we consider momentum components of the gauge field. It turns out that the broad region of momentum components is relevant for the low-lying Dirac spectrum and zero modes, i.e., topological charges. The connection with chiral random matrix theory is also discussed. Second, we consider an SU(2) subgroup component of the SU(3) gauge field. The SU(2) subgroup component behaves like the SU(2) gauge field in the low-lying Dirac spectrum.

hep-lat↗

arXiv2010

Relevant momentum components of gluons for confinement and chiral symmetry breaking

We investigate which momentum components of gluons induce color confinement and spontaneous chiral symmetry breaking in lattice QCD. For this purpose, we formulate a lattice framework to introduce the momentum cutoff of the gluon field. Using this framework, we calculate the quark-antiquark potential, the color flux tube, the chiral condensate, and the Dirac spectrum. Our results suggest that confinement and chiral symmetry breaking are induced by somehow different momentum components of gluons.

hep-lat↗

arXiv2010

Fourier analysis of the flux-tube distribution in SU(3) lattice QCD

This letter presents a novel analysis of the action/energy density distribution around a static quark-antiquark pair in SU(3) lattice quantum chromodynamics. Using the Fourier transformation of the link variable, we remove the high-momentum gluon and extract the flux-tube component from the action/energy density. When the high-momentum gluon is removed, the statistical fluctuation is drastically suppressed, and the singularities from the quark self-energy disappear. The obtained flux-tube component is broadly distributed around the line connecting the quark and the antiquark.

hep-lat↗

arXiv2010

Relevant gluonic energy scale of spontaneous chiral symmetry breaking from lattice QCD

We analyze which momentum component of the gluon field induces spontaneous chiral symmetry breaking in lattice QCD. After removing the high-momentum or low-momentum component of the gluon field, we calculate the chiral condensate and observe the roles of these momentum components. The chiral condensate is found to be drastically reduced by removing the zero-momentum gluon. The reduction is about 40% of the total in our calculation condition. The nonzero-momentum infrared gluon also has a sizable contribution to the chiral condensate. From the Banks-Casher relation, this result reflects the nontrivial relation between the infrared gluon and the zero-mode quark.

hep-lat↗

arXiv2009

Lattice QCD Analysis for Gluons

Nonperturbative properties of gluons are studied in SU(3) lattice QCD at the quenched level. The first subject is a functional-form analysis of the gluon propagator $D_{μν}^{ab}(x)$ in the Landau gauge. We find that the gluon propagator $D_{μμ}^{aa}(r)$ obtained in lattice QCD is well described by the four-dimensional (4D) Yukawa-type function $e^{-mr}/r$ with $m \simeq 600$MeV for the Euclidean 4D distance $r = 0.1 \sim 1.0$ fm. In momentum space, the gluon propagator $\tilde D_{μμ}^{aa}(p^2)$ ($p= 0.5 \sim 3$ GeV) is found to be well approximated with a new-type propagator of $(p^2+m^2)^{-3/2}$, which corresponds to 4D Fourier image of the Yukawa-type function. Associated with the Yukawa-type gluon propagator, we derive analytical expressions for the zero-spatial-momentum propagator $D_0(t)$, the effective mass $M_{\rm eff}(t)$, and the spectral function $ρ(ω)$ of the gluon field. The mass parameter $m$ turns out to be the infrared effective mass of gluons. The obtained gluon spectral function $ρ(ω)$ is almost negative-definite for $ω>m$, except for a positive $δ$-functional peak at $ω=m$. The second subject is a lattice-QCD determination of the relevant gluonic momentum-component for color confinement. As a remarkable fact, the string tension is found to be almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV in the Landau gauge. In fact, the relevant gluonic scale for color confinement is concluded to be below 1.5 GeV.

hep-lat↗

arXiv2009

Relevant energy scale of color confinement from lattice QCD

We propose a new lattice framework to extract the relevant gluonic energy scale of QCD phenomena which is based on a "cut" on link variables in momentum space. This framework is expected to be broadly applicable to all lattice QCD calculations. Using this framework, we quantitatively determine the relevant energy scale of color confinement, through the analyses of the quark-antiquark potential and meson masses. The relevant energy scale of color confinement is found to be below 1.5 GeV in the Landau gauge. In fact, the string tension is almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV. When the relevant low-energy region is cut, the quark-antiquark potential is approximately reduced to a Coulomb-like potential, and each meson becomes a quasi-free quark pair. As an analytical model calculation, we also investigate the dependence of the Richardson potential on the cut, and find the consistent behavior with the lattice result.

hep-lat↗

arXiv2008

Lattice analysis for the energy scale of QCD phenomena

We formulate a new framework in lattice QCD to study the relevant energy scale of QCD phenomena. By considering the Fourier transformation of link variable, we can investigate the intrinsic energy scale of a physical quantity nonperturbatively. This framework is broadly available for all lattice QCD calculations. We apply this framework for the quark-antiquark potential and meson masses in quenched lattice QCD. The gluonic energy scale relevant for the confinement is found to be less than 1 GeV in the Landau or Coulomb gauge.

hep-lat↗

arXiv2008

Lattice QCD study of the heavy-heavy-light quark potential

We study the heavy-heavy-light quark ($QQq$) potential in SU(3) quenched lattice QCD, and discuss one of the roles of the finite-mass valence quark in the inter-quark potential. Monte Carlo simulations are performed with the standard gauge action on the $16^4$ lattice at $β=6.0$ and the $O(a)$-improved Wilson fermion action at four hopping parameters. For statistical improvement, the gauge configuration is fixed with the Coulomb gauge. We calculate the potential energy of $QQq$ systems as a function of the inter-heavy-quark distance $R$ in the range of $R \le$ 0.8 fm. The $QQq$ potential is well described with a Coulomb plus linear potential, and the effective string tension between the two heavy quarks is significantly smaller than the string tension $σ\simeq 0.89$ GeV/fm. It would generally hold that the effect of the finite-mass valence quark reduces the inter-two-quark confinement force in baryons.

hep-lat↗

arXiv2008

Heavy-heavy-light quark potential in SU(3) lattice QCD

We perform the first study for the heavy-heavy-light quark (QQq) potential in SU(3) lattice QCD. The calculations are done with the standard gauge and $O(a)$-improved Wilson fermion action on the $16^4$ lattice at $β=6.0$ at the quenched level. We calculate the energy of QQq systems as the function of the distance between the two heavy quarks, and find that the QQq potential is well described with a Coulomb plus linear potential form. Compared to the static three-quark case, the Coulomb term does not change but the effective string tension between the heavy quarks is significantly reduced by the light-quark effect. We also investigate the light-quark mass dependence of the QQq potential using the four hopping parameters, $κ=0.1200,0.1300,0.1340$, and 0.1380. The reduction of the effective string tension is considered to be a general property for baryons and multi-quark hadrons.

hep-lat↗

arXiv2008

Heavy-heavy-light quark potential in two approaches

We perform the first study about the heavy-heavy-light quark potential in lattice QCD and a potential model. We find that the inter-two-quark confining force is reduced by valence quark motional effects compared to the string tension.

hep-ph↗

arXiv2008

Quark motional effects on the interquark potential in baryons

We study the heavy-heavy-light quark ($QQq$) system in a non-relativistic potential model, and investigate the quark motional effect on the inter-two-quark potential in baryons. We adopt the Hamiltonian with the static three-quark potential which is obtained by the first-principle calculation of lattice QCD, rather than the two-body force in ordinary quark models. Using the renormalization-group inspired variational method in discretized space, we calculate the ground-state energy of $QQq$ systems and the light-quark spatial distribution. We find that the effective string tension between the two heavy quarks is reduced compared to the static three-quark case. This reduction of the effective string tension originates from the geometrical difference between the inter-quark distance and the flux-tube length, and is conjectured to be a general property for baryons.

hep-ph↗