arXiv subjects
Publications and source records attributed to Y. Koma.
The multi-level algorithm allows, at least for pure gauge theories, reliable measurement of exponentially small expectation values. The implementation of the algorithm depends strongly on the observable one wants to measure. Here we report measurement of glueball masses using the multi-level algorithm in 4 dimensional compact U(1) theory as a case study.
The structure of the flux-tube profile in Abelian-projected (AP) SU(2) gauge theory in the maximally Abelian gauge is studied. The connection between the AP flux tube and the classical flux-tube solution of the U(1) dual Abelian Higgs (DAH) model is clarified in terms of the path-integral duality transformation. This connection suggests that the electric photon and the magnetic monopole parts of the Abelian Wilson loop can act as separate sources creating the Coulombic and the solenoidal electric field inside a flux tube. The conjecture is confirmed by a lattice simulation which shows that the AP flux tube is composed of these two contributions.
The finite temperature lattice QCD with N_f=2 nonperturbatively improved Wilson fermions is studied on 16^3 8 lattice. Using abelian projection after fixing to MA gauge we determine the transition temperature for m_π/m_ρ \sim 0.8.
Results of the study of lattice QCD with two flavors of nonperturbatively improved Wilson fermions at finite temperature are presented. The transition temperature for m_π/m_ρ \sim 0.8 and lattice spacing a \sim 0.12 fm is determined. A two-exponent ansatz is successfully applied to describe the heavy quark potential in the confinement phase.
We study the profile of the broken string (flux tube) in the maximally abelian gauge below and above the finite temperature phase transition in full QCD. In the deconfinement phase, the flux tube disappears and the electric field apperas to be Coulomb-like. In the confinement phase, but near $T_c$, at shorter distances a flux tube is formed like at zero temperature, while at larger distances the tube disappears similar to the deconfinement phase.
We reconsider the properties of the $Q\bar{Q}$ flux tube within Abelian-projected SU(2) lattice gauge theory in terms of electric field and monopole current. In the maximal Abelian gauge we assess the influence of the Gribov copies on the apparent flux-tube profile. For the optimal gauge fixing we study the independence of the profile on the lattice spacing for $β=$ 2.3, 2.4, and 2.5115 on a $32^4$ lattice. We decompose the Abelian Wilson loop into monopole and photon parts and compare the electric and monopole profile emerging from different sources with the field strength and monopole current within the dual Ginzburg-Landau theory.
We study N_f=2 lattice QCD with nonperturbatively improved Wilson fermions at finite temperature on 16^3 \cdot 8 lattices. We determine the transition temperature at m_π/m_ρ \sim 0.8 and lattice spacing as small as 0.12fm. The string breaking at T < T_c is also studied. We find that the static potential can be fitted by a simple expression involving string model potential at finite temperature.
We present first results on the dynamics of monopoles in full QCD with N_f=2 flavors of dynamical quarks. Among the quantities being studied are the monopole density and the monopole screening length, the static potential as well as the profile of the color electric flux tube. Furthermore, we derive the low-energy effective monopole action.
Three topics of monopole dynamics in gluodynamics are presented. 1)Gauge (in)dependence of the monopole effective action (S.Ito, T.W.Park, T.Suzuki): Four different abelian projections are studied. MA and Laplacian abelian gauges show almost the same renormalization flow and renormalized trajectory. 2)The quantized dual abelian Higgs model (DAH) derived from SU(2) gluodynamics and its vacuum structure (Y.Koma, E.-M.Ilgenfritz, T.Suzuki,M.I.Polikarpov): Monte-Carlo analysis of DAH is done. The quantum average of the dual field strength shows a flux tube profile similar to the color-electric field profile measured in SU(2) gluodynamics. 3)Lattice instanton action from 3D SU(2) Georgi-Glashow model (GG)$_3$ (T.Yazawa, T.Suzuki): (GG)$_3$ is studied on the lattice in the London limit. We determine an effective instanton action both in unitary and MA gauges. For some range of parameters, we obtain almost perfect actions which look the same in both gauges (gauge independence) and which reproduce well the string tension.
The string tensions of flux tubes associated with static charges in various SU(3) representations are studied within the dual Ginzburg-Landau (DGL) theory. The ratios of the string tensions between higher and fundamental representations, $d_{D} \equiv σ_{D}/σ_{F}$, are found to depend only on the Ginzburg-Landau (GL) parameter, $κ= m_χ/m_{B}$, the mass ratio between monopoles $m_χ$ and dual gauge bosons $m_B$. In the case of the Bogomol'nyi limit ($κ=1$), analytical values of $d_{D}$ are easily obtained by adopting the manifestly Weyl invariant formulation of the DGL theory, which are provided simply by the number of color-electric Dirac strings inside the flux tube. A numerical investigation of the ratio for various GL-parameter cases is also performed, which suggests that the Casimir scaling is obtained in the type-II parameter range within the interval $κ=5 \sim 9$ for various ratios $d_D$.
Hadronic flux-tube solutions describing the mesonic and the baryonic states within the dual Ginzburg-Landau (DGL) theory are investigated by using the dual lattice formulation in the Weyl-symmetric approach. The shape of the flux tubes is determined by placement of the color-electric Dirac-string singularity treated as a connected stack of quantized plaquettes in the dual lattice formulation. The Weyl symmetric profiles of the hadronic flux tubes are obtained by using the manifestly Weyl invariant representation of the dual gauge field.
We study abelian dominance and monopole condensation for the quark confinement physics using the lattice QCD simulations in the MA gauge. These phenomena are closely related to the dual superconductor picture of the QCD vacuum, and enable us to construct the dual Ginzburg-Landau (DGL) theory as an useful effective theory of nonperturbative QCD. We then apply the DGL theory to the studies of the low-lying hadron structure and the scalar glueball properties.
We study the nonperturbative QCD in terms of topological objects, i.e., QCD-monopoles and instantons. In the 't Hooft abelian gauge, QCD is reduced into an abelian gauge theory with QCD-monopoles, and the confinement mechanism can be understood with the dual superconductor picture. Regarding the flux-tube ring as the glueball, we study the glueball properties by combining the dual Ginzburg-Landau theory and the Nambu-Goto action. We find the strong correlations between instantons and monopole world-lines both in the continuum theory and in the lattice QCD. The nonperturbative QCD vacuum is filled with instantons and monopoles, and dense instantons generate a macroscopic network of the monopole world-line, which would be responsible for the confinement force in the infrared region.