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Wolfram Schroers

Publications and source records attributed to Wolfram Schroers.

11 recordsLinked to original sources
arXiv2010

Nucleon structure from mixed action calculations using 2+1 flavors of asqtad sea and domain wall valence fermions

We present high statistics results for the structure of the nucleon from a mixed-action calculation using 2+1 flavors of asqtad sea and domain wall valence fermions. We perform extrapolations of our data based on different chiral effective field theory schemes and compare our results with available information from phenomenology. We discuss vector and axial form factors of the nucleon, moments of generalized parton distributions, including moments of forward parton distributions, and implications for the decomposition of the nucleon spin.

hep-lat↗
arXiv2009

Nucleon form factors on the lattice with light dynamical fermions

The electromagnetic form factors provide important insight into the internal structure of the nucleon and continue to be of major interest for experiment and phenomenology. For an intermediate range of momenta the form factors can be calculated on the lattice. However, the reliability of the results is limited by systematic errors mostly due to the required extrapolation to physical quark masses. Chiral effective field theories predict a rather strong quark mass dependence in a range which was yet inaccessible for lattice simulations. We give an update on recent results from the QCDSF collaboration using gauge configurations with dynamical Nf=2, non-perturbatively O(a)-improved Wilson fermions at pion masses as low as 350 MeV.

hep-lat↗
arXiv2008

Hadronic structure from the lattice

In recent years the investigation of hadron structure using lattice techniques has attracted growing attention. In this talk we give an overview on recent work with a focus on results for nucleon spectrum and structure from the QCDSF collaboration.

hep-lat↗
arXiv2007

Understanding nucleon structure using lattice simulations

This review focuses on the discussion of three key results of nucleon structure calculations on the lattice. These three results are the quark contribution to the nucleon spin, J_q, the nucleon-Delta transition form factors, and the nucleon axial coupling, g_A. The importance for phenomenology and experiment is discussed and the requirements for future simulations are pointed out.

hep-lat↗
arXiv2005

What the lattice can tell us about nucleon structure

This review focuses on the current status of lattice calculations of three observables which are both phenomenologically and experimentally relevant and have been scrutinized recently. These three observables are the nucleon electromagnetic form factors, the momentum fraction, , and the nucleon axial coupling, gA.

hep-lat↗
arXiv2005

A study of the N to Delta transition form factors in full QCD

The N to Delta transition form factors GM1, GE2 and GC2 are evaluated using dynamical MILC configurations and valence domain wall fermions at three values of quark mass corresponding to pion mass 606 MeV, 502 MeV and 364 MeV on lattices of spatial size $20^3$ and $28^3$. The unquenched results are compared to those obtained at similar pion mass in the quenched theory.

hep-lat↗
arXiv2005

Hadron structure with light dynamical quarks

Generalized parton distributions encompass a wealth of information concerning the three-dimensional quark and gluon structure of the nucleon, and thus provide an ideal focus for the study of hadron structure using lattice QCD. The special limits corresponding to form factors and parton distributions are well explored experimentally, providing clear tests of lattice calculations, and the lack of experimental data for more general cases provides opportunities for genuine predictions and for guiding experiment. We present results from hybrid calculations with improved staggered (Asqtad) sea quarks and domain wall valence quarks at pion masses down to 350 MeV.

hep-lat↗
arXiv2005

Parton distributions from the lattice

I review the current status of lattice calculations for two selected observables related to nucleon structure: the second moment of the unpolarized parton distribution, (u-d), and the first moment of the polarized parton distribution, the non-singlet axial coupling gA. The major challenge is the requirement to extract them sufficiently close to the chiral limit. In the former case, there still remains a puzzling disagreement between lattice data and experiment. For the latter quantity, however, we may be close to obtaining its value from the lattice in the immediate future.

hep-ph↗
arXiv2003

Moments of Nucleon Generalized Parton Distributions in Lattice QCD

Calculation of moments of generalized parton distributions in lattice QCD requires more powerful techniques than those previously used to calculate moments of structure functions. Hence, we present a novel approach that exploits the full information content from a given lattice configuration by measuring an overdetermined set of lattice observables to provide maximal statistical constraints on the generalized form factors at a given virtuality, t. In an exploratory investigation using unquenched QCD configurations at intermediate sea quark masses, we demonstrate that our new technique is superior to conventional methods and leads to reliable numerical signals for the n=2 flavor singlet generalized form factors up to 3 GeV^2. The contribution from connected diagrams in the flavor singlet sector to the total quark angular momentum is measured to an accuracy of the order of one percent.

hep-lat↗
arXiv2003

Advanced Algorithms for the Simulation of Gauge Theories with Dynamical Fermionic Degrees of Freedom

This thesis is focused on the implementation and the application of a novel kind of algorithm which is expected to overcome the limitations of older schemes. This new algorithm is named Multiboson Method. It allows to simulate an arbitrary number of dynamical fermion flavors, which can in principle have different masses. It will be shown that it exhibits better scaling properties for light fermions than other methods. Therefore, it has the potential to become the method of choice.

hep-lat↗