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E. -M. Ilgenfritz

Publications and source records attributed to E. -M. Ilgenfritz.

At least 145 records · Page 8Linked to original sources
arXiv2002

Parallel tempering in full QCD with Wilson fermions

We study the performance of QCD simulations with dynamical Wilson fermions by combining the Hybrid Monte Carlo algorithm with parallel tempering on $10^4$ and $12^4$ lattices. In order to compare tempered with standard simulations, covariance matrices between sub-ensembles have to be formulated and evaluated using the general properties of autocorrelations of the parallel tempering algorithm. We find that rendering the hopping parameter $κ$ dynamical does not lead to an essential improvement. We point out possible reasons for this observation and discuss more suitable ways of applying parallel tempering to QCD.

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arXiv2001

Classical solutions with nontrivial holonomy in SU(2) LGT at T \ne 0

We generate SU(2) lattice gauge fields at finite temperature and cool them in order to characterize the two phases by the occurrence of specific classical solutions.We apply two kinds of spatial boundary conditions: fixed holonomy and standard periodic b.c. For T < T_c our findings concerning classical configurations semi-quantitatively agree for both types of boundary conditions. We find in the confinement phase a mixture of undissociated calorons with lumps of positive or negative half-integer topological charges.

hep-lat↗
arXiv2001

Topics of monopole dynamics in gluodynamics

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.

hep-lat↗
arXiv2001

Singular gauge potentials and the gluon condensate at zero temperature

We consider a new cooling procedure which separates gluon degrees of freedom from singular center vortices in SU(2) LGT in a gauge invariant way. Restricted by a cooling scale $κ^4/σ^2$ fixing the residual SO(3) gluonic action relative to the string tension, the procedure is RG invariant. In the limit $κ\to 0$ a pure Z(2) vortex texture is left. This {\it minimal} vortex content does not contribute to the string tension. It reproduces, however, the lowest glueball states. With an action density scaling like $a^4$ with $β$, it defines a finite contribution to the action density at T=0 in the continuum limit. We propose to interpret this a mass dimension 4 condensate related to the gluon condensate. Similarly, this vortex texture is revealed in the Landau gauge.

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arXiv2001

Monopoles, confinement and deconfinement in lattice compact QED in (2+1)D with external fields

Finite temperature compact electrodynamics in (2+1) dimensions is studied in the presence of external electromagnetic fields. The deconfinement temperature is found to be insensitive to the external fields. This result corroborates our observation that external fields create additional small--size magnetic dipoles from the vacuum which do not spoil the confining properties of the model at low temperature. However, the Polyakov loop is not an order parameter of confinement. It can vanish in deconfinement in the presence of external field. This does not mean the restoration of confinement for certain external field fluxes. As a next step in the study of (2+1)D QED, the influence of monopoles on the photon propagator is studied. First results are presented showing this connection in the confining phase (without external field).

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arXiv2001

Gauge potential singularities and the gluon condensate at finite temperatures

The continuum limit of SU(2) lattice gauge theory is carefully investigated at zero and at finite temperatures. It is found that the continuum gauge field has singularities originating from center degrees of freedom being discovered in Landau gauge. Our numerical results show that the density of these singularities properly extrapolates to a non-vanishing continuum limit. The action density of the non-trivial Z_2 links is tentatively identified with the gluon condensate. We find for temperatures larger than the deconfinement temperature that the thermal fluctuations of the embedded Z_2 gauge theory result in an increase of the gluon condensate with increasing temperature.

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arXiv2001

Monopoles, confinement and deconfinement of (2+1)D compact lattice QED in external fields

The compact Abelian model in three space--time dimensions is studied in the presence of external electromagnetic fields at finite temperatures. We show that the deconfinement phase transition is independent on the strength of the external fields. This result is in agreement with our observation that the external fields create small--size magnetic dipoles from the vacuum which do not influence the confining properties of the model. Contrary to the deconfinement phase, the internal field in the direction of the applied external field is attenuated in the confinement phase, this screening becomes stronger with decreasing temperature.

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arXiv2001

A lattice study of 3D compact QED at finite temperature

We study the deconfinement phase transition and monopole properties in the finite temperature 3D compact Abelian gauge model on the lattice. We predict the critical coupling as function of the lattice size in a simplified model to describe monopole binding. We demonstrate numerically that the monopoles are sensitive to the transition. In the deconfinement phase the monopoles appear in the form of a dilute gas of magnetic dipoles. In the confinement phase both monopole density and string tension differ from semiclassical estimates if monopole binding is neglected. However, the analysis of the monopole clusters shows that the relation between the string tension and the density of monopoles in charged clusters is in reasonable agreement with those predictions. We study the cluster structure of the vacuum in both phases of the model.

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arXiv2001

Casimir scaling in a dual superconducting scenario of confinement

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 $d_D$.

hep-ph↗
arXiv2001

Weyl symmetric representation of hadronic flux tubes in the dual Ginzburg-Landau theory

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.

hep-ph↗
arXiv2001

Gauge invariant Z_2 vortex vacuum textures and the SU(2) gluon condensate

For SU(2) lattice gauge theory, a new SO(3) cooling procedure is proposed which removes the SU(2)/Z(2) coset fields from the lattice configurations and reveals a Z(2) vortex vacuum texture different from the P-vortex content obtained in the maximal center gauge. Cooling can be restricted in a renormalization group invariant way by a parameter controlling the remaining SO(3) action density. A gauge invariant Z(2) vortex vacuum emerges asymptotically if cooling is not restricted. This ``vortex texture'' does not support the string tension or a finite part of it. The SU(2) action density associated with the new Z(2) vortex texture has a smooth extrapolation to the continuum limit. We propose an interpretation as a mass dimension four condensate related to the gluon condensate featuring in the operator product expansion.

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arXiv2001

Abelian Monopole and Center Vortex Views at the Multi-Instanton Gas

We consider full non-Abelian, Abelian and center projected lattice field configurations built up from random instanton gas configurations in the continuum. We study the instanton contribution to the $\bar{Q}Q$ force with respect to ({\it i}) instanton density dependence, ({\it ii}) Casimir scaling and ({\it iii}) whether various versions of Abelian dominance hold. We check that the dilute gas formulation for the interaction potential gives an reliable approximation only for densities small compared to the phenomenological value. We find that Casimir scaling does not hold, confirming earlier statements in the literature. We show that the lattice used to discretize the instanton gas configurations has to be sufficiently coarse ($a \approx 2\barρ$ compared with the instanton size $\barρ$) such that maximal Abelian gauge projection and center projection as well as the monopole gas contribution to the $\bar{Q}Q$ force reproduce the non-Abelian instanton-mediated force in the intermediate range of linear quasi-confinement. We demonstrate that monopole clustering also depends critically on the discretization scale confirming earlier findings based on monopole blocking.

hep-ph↗
arXiv2000

Half-integer topological charges below and above the deconfinement transition?

For pure SU(2) lattice gauge theory at finite T, by the help of the cooling method, we search for classical (approximate) solutions having non-trivial holonomy at the spatial boundary. We identify various typical objects and provide their relative frequency of occurence for the confinement and deconfinement phases. Among the configurations obtained we see also the dissociated BPS monopole pairs recently discussed by van Baal and collaborators.

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arXiv2000

Transverse QCD Dynamics Near the Light Cone

Starting from the QCD Hamiltonian in near-light cone coordinates, we study the dynamics of the gluonic zero modes. Euclidean 2+1 dimensional lattice simulations show that the gap at strong coupling vanishes at intermediate coupling. This result opens the possibility to synchronize the continuum limit with the approach to the light cone.

hep-ph↗
arXiv2000

Field strength correlators in the instanton gas: The importance of the two-instanton contribution

The field strength correlators at zero temperature are semi-classically evaluated fitting the random instanton liquid model to lattice data for quenched SU(3) lattice gauge theory. We restrict ourselves to the lowest order in an instanton density expansion necessary to explain the difference between transverse and longitudinal correlation functions. In the instanton-instanton and instanton-antiinstanton contributions the Schwinger line factors neglected in a previous analysis are numerically taken into account in a weighted Monte Carlo evaluation. This leads to different estimates for instanton size and density. A reasonable description of the correlators within the intermediate range from 0.4 fm to 1 fm is obtained.

hep-ph↗
arXiv1999

Embedded vortices and their interactions at electroweak crossover

We study properties of Z-vortices in the crossover region of the 3D SU(2) Higgs model. Correlators of the vortex currents with gauge field energy and Higgs field squared ("quantum vortex profile") reveal a structure that can be compared with a classical vortex. We define a core size and a penetration depth from the vortex profile. Z-vortices are found to interact with each other analogously to Abrikosov vortices in a type-I superconductor.

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