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T. Streuer

Publications and source records attributed to T. Streuer.

At least 37 records · Page 2Linked to original sources
arXiv2007

Exploring the structure of the quenched QCD vacuum with overlap fermions

Overlap fermions have an exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects of quenched gauge field configurations. This includes the localization and chiral properties of the eigenmodes, the local structure of the ultraviolet filtered field strength tensor, as well as the structure of topological charge fluctuations. We conclude that the vacuum has a multifractal structure.

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arXiv2006

Vacuum structure as seen by overlap fermions

Three complementary views on the QCD vacuum structure, all based on eigenmodes of the overlap operator, are reported in their interrelation: (i) spectral density, localization and chiral properties of the modes, (ii) the possibility of filtering the field strength with the aim to detect selfdual and antiselfdual domains and (iii) the various faces of the topological charge density, with and without a cutoff λ_{\rm cut} = O(Λ_{QCD}). The techniques are tested on quenched SU(3) configurations.

hep-lat↗
arXiv2006

The QCD vacuum probed by overlap fermions

We summarize different uses of the eigenmodes of the Neuberger overlap operator for the analysis of the QCD vacuum, here applied to quenched configurations simulated by means of the Luescher-Weisz action. We describe the localization and chiral properties of the lowest modes. The overlap-based topological charge density (with and without UV-filtering) is compared with the results of UV-filtering for the field strength tensor. The latter allows to identify domains of good (anti-)selfduality. All these techniques together lead to a dual picture of the vacuum, unifying the infrared instanton picture with the presence of singular defects co-existent at different scales.

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arXiv2006

Probing the topological structure of the QCD vacuum with overlap fermions

Overlap fermions implement exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects on Luescher-Weisz-type quenched gauge field configurations using overlap fermions as a probe. Particular emphasis is placed upon the analysis of the spectral density and the localisation properties of the eigenmodes as well as on the local structure of topological charge fluctuations.

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arXiv2006

Simulating at Realistic Quark Masses: Light quark masses

We present new results for light quark masses. The calculations are performed using two flavours of $O(a)$ improved Wilson fermions. We have reached lattice spacings as small as $a \sim 0.07$fm and pion masses down to $m_π \sim 340$MeV in our simulations. This gives us significantly better control on the chiral and continuum extrapolations.

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arXiv2006

Simulating at Realistic Quark Masses: Pseudoscalar Decay Constants and Chiral Logarithms

Due to improvements in computer performance and algorithms, the rapidly increasing cost for unquenched Wilson-type fermions with lighter quarks has been ameliorated and new simulations are now possible. Here we present results using two flavours of O(a)-improved Wilson fermions for meson decay constants at pseudoscalar masses down to 320MeV. Results are at several lattice spacings down to about 0.07fm and include a non-perturbative determination of the renormalisation constant. This enables us to attempt contact with (partially quenched) chiral perturbation theory.

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arXiv2006

Hadron spectrum, quark masses and decay constants from light overlap fermions on large lattices

We present results from a simulation of quenched overlap fermions with Lüscher-Weisz gauge field action on lattices up to $24^3 48$ and for pion masses down to $\approx 250$ MeV. Among the quantities we study are the pion, rho and nucleon masses, the light and strange quark masses, and the pion decay constant. The renormalization of the scalar and axial vector currents is done nonperturbatively in the $RI-MOM$ scheme. The simulations are performed at two different lattice spacings, $a \approx 0.1$ fm and $\approx 0.15$ fm, and on two different physical volumes, to test the scaling properties of our action and to study finite volume effects. We compare our results with the predictions of chiral perturbation theory and compute several of its low-energy constants. The pion mass is computed in sectors of fixed topology as well.

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arXiv2005

Nucleon Structure from Quenched Overlap Fermions

We compute the lowest moments of the nucleon's structure functions using quenched overlap fermions at two different lattice spacings. The renormalisation is done nonperturbatively in the RI'-MOM-scheme.

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arXiv2005

Probing the chiral phase transition of N_f=2 clover fermions with valence overlap fermions

Overlap fermions are a powerful tool for investigating the chiral and topological structure of the vacuum and the thermal states of QCD. We study various chiral and topological aspects of the finite temperature phase transition of N_f=2 flavours of O(a) improved Wilson fermions, using valence overlap fermions as a probe. Particular emphasis is placed upon the analysis of the spectral density and the localisation properties of the eigenmodes as well as on the local structure of topological charge fluctuations in the vicinity of the chiral phase transition. The calculations are done on 16^3x8 lattices generated by the DIK collaboration.

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arXiv2005

Non-perturbative renormalisation for overlap fermions

Using non-perturbative techniques we have found the renormalisation factor, Z, in the RI-MOM scheme for quark bilinear operators in quenched QCD. We worked with overlap fermions using the Luescher-Weisz gauge action. Our calculation was performed at beta=8.45 at a lattice spacing of 1/a=2.1 GeV using a value of rho=1.4. Our results show good agreement between the vector and the axial vector in the zero mass limit. This shows that overlap fermions have good chiral properties. To attempt to improve the discretisation errors in our results we subtracted the O(a^2) terms in one-loop lattice perturbation theory from the Monte Carlo Green functions. In particular we paid attention to the operators for the observable . We found a value for the renormalisation constants Z^msbar_(v_2b) and Z^msbar_(v_2a) just less than 1.9 at mu=1/a=2.1 GeV.

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arXiv2005

Localization properties of the topological charge density and the low lying eigenmodes of overlap fermions

Overlap fermions, which preserve exact chiral symmetry on the lattice, provide a powerful tool for investigating the topological structure of the vacuum. Applying this formulation to zero-temperature quenched SU(3) configurations generated by means of the Luescher-Weisz action, we define the topological charge density with and without UV filtering and study its properties by looking at the density profile and the two-point correlation function. We observe that the density possesses global sign coherent structures, which get increasingly tangled as more and more modes are included. This change of the structure is also detected by the increasing negative tail of the two-point function. We also study the inverse participation ratio of the eigenmodes and discuss their dimensionality.

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arXiv2004

Baryonic Flux in Quenched and Two-Flavor Dynamical QCD after Abelian projection

We study the distribution of color electric flux of the three-quark system in quenched and full QCD (with N_f = 2 flavors of dynamical quarks) at zero and finite temperature. To reduce ultra-violet fluctuations, the calculations are done in the abelian projected theory fixed to the maximally abelian gauge. In the confined phase we find clear evidence for a Y--shape flux tube surrounded and formed by the solenoidal monopole current, in accordance with the dual superconductor picture of confinement. In the deconfined, high temperature phase monopoles cease to condense, and the distribution of the color electric field becomes Coulomb--like.

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arXiv2004

Structure functions and form factors close to the chiral limit from lattice QCD

Results for nucleon matrix elements (arising from moments of structure functions) and form factors from a mixture of runs using Wilson, clover and overlap fermions (both quenched and unquenched) are presented and compared in an effort to explore the size of the chiral `regime', lattice spacing errors and quenching artefacts. While no run covers this whole range of effects the partial results indicate a picture of small lattice spacing errors, small quenching effects and only reaching the chiral regime at rather light quark masses.

hep-lat↗
arXiv2004

Quark spectra and light hadron phenomenology from overlap fermions with improved gauge field action

We present first results from a simulation of quenched overlap fermions with improved gauge field action. Among the quantities we study are the spectral properties of the overlap operator, the chiral condensate and topological charge, quark and hadron masses, and selected nucleon matrix elements. To make contact with continuum physics, we compute the renormalization constants of quark bilinear operators in perturbation theory and beyond.

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arXiv2003

Dynamics of Monopoles and Flux Tubes in Two-Flavor Dynamical QCD

We investigate the confining properties of the QCD vacuum with $N_f=2$ flavors of dynamical quarks, and compare the results with the properties of the quenched theory. We use non-perturbatively $\mathcal{O}(a)$ improved Wilson fermions to keep cut-off effects small. We focus on color magnetic monopoles. Among the quantities we study are the monopole density and the monopole screening length, the static potential and the profile of the color electric flux tube. We furthermore derive the low-energy effective monopole action. Marked differences between the quenched and dynamical vacuum are found.

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arXiv2002

Flux Tubes of Two- and Three-Quark System in Full QCD

We study the abelian color flux of two- and three-quark systems in the maximally abelian gauge in lattice QCD with dynamical fermions. We find that the abelian flux tube formed between quark and antiquark is very much the same as in quenched QCD up to quark separations of $R$$\sim$ 2fm. The profile of the color electric field in three-quark system suggests $Y$ ansatz, which might be interpreted as the result of the vacuum pressure in the confined phase. In order to clarify the flux structure, we investigate the color electric field of the three-quark system splittting the abelian gauge field into the monopole and photon parts.

hep-lat↗
arXiv2002

The flux distribution of the three quark system in SU(3)

We study the abelian color-flux distribution of the three quark system in the maximally abelian gauge on SU(3) lattices. The distribution of the color electric field suggests $Y Ansatz$, which might be interpreted through the dual superconductor picture as the result of the vacuum pressure in the confined phase. In order to clarify the flux structure, we investigate the color electric field in the three quark system also in the monopole part and in the photon part.

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