Searcharxiv⌕ Search

arXiv subjects

Manfried Faber

Publications and source records attributed to Manfried Faber.

At least 55 records · Page 3Linked to original sources
arXiv2005

Lattice QCD at finite density via a new canonical approach

We carry out a finite density calculation based on a canonical approach which is designed to address the overlap problem. Two degenerate flavor simulations are performed using Wilson gauge action and Wilson fermions on $4^4$ lattices, at temperatures close to the critical temperature $T_c\approx 170\MeV$ and large densities (5 to 20 times nuclear matter density). In this region, we find that the algorithm works well. We compare our results with those from other approaches.

hep-lat↗
arXiv2004

Progress on a canonical finite density algorithm

We test the finite density algorithm in the canonical ensemble which combines the HMC update with the accept/reject step according to the ratio of the fermion number projected determinant to the unprojected one as a way of avoiding the determinant fluctuation problem. We report our preliminary results on the Polyakov loop in different baryon number sectors which exhibit deconfinement transitions on small lattices. The largest density we obtain around $T_c$ is an order of magnitude larger than that of nuclear matter. From the conserved vector current, we calculate the quark number and verify that the mixing of different baryon sectors is small.

hep-lat↗
arXiv2004

Electrodynamic Limit in a Model for Charged Solitons

We consider a model of topological solitons where charged particles have finite mass and the electric charge is quantised already at the classical level. In the electrodynamic limit, which physically corresponds to electrodynamics of solitons of zero size, the Lagrangian of this model has two degrees of freedom only and reduces to the Lagrangian of the Maxwell field in dual representation. We derive the equations of motion and discuss their relations with Maxwell's equations. It is shown that Coulomb and Lorentz forces are a consequence of topology. Further, we relate the U(1) gauge invariance of electrodynamics to the geometry of the soliton field, give a general relation for the derivation of the soliton field from the field strength tensor in electrodynamics and use this relation to express homogeneous electric fields in terms of the soliton field.

hep-th↗
arXiv2003

Center Dominance in SU(2) Gauge-Higgs Theory

We study the SU(2) gauge-Higgs system in D=4 dimensions, and analyze the influence of the fundamental-representation Higgs field on the vortex content of the gauge field. It is shown that center projected Polyakov lines, at low temperature, are finite in the infinite volume limit, which means that the center vortex distribution is consistent with color screening. In addition we confirm and further investigate the presence of a "Kertesz-line" in the strong-coupling region of the phase diagram, which we relate to the percolation properties of center vortices. It is shown that this Kertesz-line separates the gauge-Higgs phase diagram into two regions: a confinement-like region, in which center vortices percolate, and a Higgs region, in which they do not. The free energy of the gauge-Higgs system, however, is analytic across the Kertesz line.

hep-lat↗
arXiv2003

New Family of Exotic $Θ$-Baryons

From the interpretation of the $Θ^+$ baryon resonance as an excitation of the ``skyrmion liquid'' with SU(3) flavor symmetry $\bar{10}$ we deduce a new series of baryons, $Θ_1^{++}$, $Θ_1^{+}$ and $Θ_1^0$, situated at the top of the 27-plet of SU(3) flavor, with hypercharge Y=2, isospin T=1 and spin $J=\frac32$. The mass of $Θ_1$ is estimated 55 MeV/c^2 higher then the mass of $Θ^+$ and its width at 80 MeV. We also discuss the other baryons from the 27-plet.

hep-ph↗
arXiv2002

Vortices, Confinement and Higgs fields

We review lattice evidence for the vortex mechanism of quark confinement and study the influence of charged matter fields on the vortex distribution.

hep-lat↗
arXiv2001

Vortices in the SU(2)-Higgs model -- Vortices and the covariant adjoint Laplacian

Vortices in the SU(2)--Higgs model: The presence of a fundamental Higgs in the SU(N)-Higgs model yields color screening at some finite distance. Whereas the transition to the Higgs "phase" is accompanied by a suppression of projected center vortices, there is nearly no influence of color screening on the vortex properties in the confined "phase". Hence the behavior of the Wilson loop can be described in both phases within the vortex picture of confinement. Vortices and the covariant adjoint Laplacian: Laplacian center gauge is a method to localize center vortices in SU(N) gauge theory. We show that the eigenvectors of the covariant adjoint Laplacian identify vortices for a special class of gauge field configurations. However, for Monte Carlo generated configurations, modified approaches are required.

hep-lat↗
arXiv2001

Susceptibility of Monte-Carlo Generated Projected Vortices

We determine the topological susceptibility from center projected vortices and demonstrate that the topological properties of the SU(2) Yang-Mills vacuum can be extracted from the vortex content. We eliminate spurious ultraviolet fluctuations by two different smoothing procedures. The extracted susceptibility is comparable to that obtained from full field configurations.

hep-lat↗
arXiv2000

A Model for Topological Fermions

We introduce a model designed to describe charged particles as stable topological solitons of a field with values on the internal space S^3. These solitons behave like particles with relativistic properties like Lorentz contraction and velocity dependence of mass. This mass is defined by the energy of the soliton. In this sense this model is a generalisation of the sine-Gordon model from 1+1 dimensions to 3+1 dimensions, from S^1 to S^3. (We do not chase the aim to give a four-dimensional generalisation of Coleman's isomorphism between the Sine-Gordon model and the Thirring model which was shown in 2-dimensional space-time.) For large distances from the center of solitons this model tends to a dual U(1)-theory with freely propagating electromagnetic waves. Already at the classical level it describes important effects, which usually have to be explained by quantum field theory, like particle-antiparticle annihilation and the running of the coupling.

hep-th↗
arXiv2000

Center vortices in MCG - finite-size and gauge-copy effects

In SU(2) lattice gauge theory in maximal center gauge, we investigate the dependence of center-projected Creutz ratios and the vortex density on lattice size and the number of gauge copies. The dependence on the number of copies is rather strong on small lattices, but almost disappears on lattices sufficiently large compared to the expected average vortex thickness. The center-projected string tension, evaluated on sufficiently large lattices, is in good agreement with the full asymptotic string tension, and the vortex density scales according to the second-order asymptotic-freedom formula.

hep-lat↗
arXiv1998

Dual lattice simulations of flux tubes

Abelian gauge theories formulated on a space-time lattice can be used as a prototype for investigating the confinement mechanism. In U(1) lattice gauge theory it is possible to perform a dual transformation of the path integral. Simulating the obtained dual theory (which corresponds to a certain limit of a dual Higgs model) including external sources, we perform a very accurate analysis of flux tubes with respect to the dual superconductor picture. Dual flux tube simulations are also performed in the full Abelian Higgs model, in order to obtain non-perturbative control over quantum and string fluctuations, and for a comparison to the results of dual QCD.

hep-lat↗
arXiv1997

Flux tubes and their interaction in U(1) lattice gauge theory

We investigate singly and doubly charged flux tubes in U(1) lattice gauge theory. By simulating the dually transformed path integral we are able to consider large flux tube lengths, low temperatures, and multiply charged systems without loss of numerical precision. We simulate flux tubes between static sources as well as periodically closed flux tubes, calculating flux tube profiles, the total field energy and the free energy. Our main results are that the string tension in both three and four dimensions scales proportionally to the charge -- which is in contrast to previous lattice results -- and that in four-dimensional U(1) there is an attractive interaction between flux tubes for beta approaching the phase transition.

hep-lat↗
arXiv1997

Investigating Confinement in Dually Transformed U(1) Lattice Gauge Theory

The dually transformed path integral of four-dimensional U(1) lattice gauge theory is used for the calculation of expectation values in the presence of external charges. Applying the dual simulation to flux tubes for charge distances up to around 20 lattice spacings, we find a deviation from the behaviour of a dual type-II superconductor in the London limit at large distances. The roughening of the flux tube agrees with the effective string picture of confinement. Further we show that finite temperature effects are negligible for time extents larger than the charge distance. Finally we analyze the different contributions to the total energy of the electromagnetic field. The parallel component of the magnetic field turns out to have the strongest influence on the deviation from the linear behaviour at small charge distances.

hep-lat↗
arXiv1996

Field Strength and Monopoles in Dual U(1) Lattice Gauge Theory

In any Abelian gauge theory with an action periodic in the link variables one can perform a duality transformation not only in the partition function, but also in correlation functions including Polyakov loops. The calculation of expectation values in the confinement phase, like electric field strength or monopole currents in the presence of external charges, becomes significantly more efficient simulating the dual theory. We demonstrate this using the ordinary Wilson action. This approach also allows a quantitative analysis of the dual superconductor model, because the dual transformed U(1) theory can be regarded as limit of a dual non-compact Abelian Higgs model. In this way we also try to interpret the behaviour of monopole condensate and string fluctuations. Finally we present some applications for simulating the dual U(1) gauge theory.

hep-lat↗
arXiv1996

Magnetic Monopoles and the Dual London Equation in SU(3) Lattice Gauge Theory

We propose a method for the determination of magnetic monopole currents in non-Abelian gauge theories which does not need a projection to Abelian degrees of freedom. With this definition we are able to determine the distribution of magnetic currents and electric fields for the gluonic flux tube between a pair of static charges. Further we check the validity of the Gauss law and the dual London equation in a gauge invariant formulation.

hep-lat↗
arXiv1995

Monopole Currents in U(1) Lattice Gauge Theory: A Comparison to an Effective Model based on Dual Superconductivity

We compare U(1) lattice gauge theory to an effective model of Maxwell and London equations. In the effective model there is only one free parameter, the London penetration depth lambda. It turns out that one can get good agreement between both models if one modifies the usual definition of magnetic monopole currents in U(1) lattice gauge theory. This comparison also shows that already at small distances fluctuations of the occuring string are important. Further, we investigate the beta-dependence of the penetration depth and determine the suppression of the monopole condensate in flux tubes.

hep-lat↗