arXiv subjects

Simon Dinter

Publications and source records attributed to Simon Dinter.

10 recordsLinked to original sources

arXiv2013

Strangeness of the nucleon from Lattice Quantum Chromodynamics

We present a non-perturbative calculation of the strangeness of the nucleon $y_N$ within the framework of lattice QCD. This observable is known to be an important cornerstone to interpret results from direct dark matter detection experiments. We perform a lattice computation for $y_N$ with an analysis of systematic effects originating from discretization, finite size, chiral extrapolation and excited state effects leading to the value of $y_N= 0.173(50)$. The rather large uncertainty of this value of $y_N$ is dominated by systematic uncertainties which we were able to quantify in this work.

hep-lat↗

arXiv2013

A Stochastic Method for Computing Hadronic Matrix Elements

We present a stochastic method for the calculation of baryon three-point functions that is more versatile compared to the typically used sequential method. We analyze the scaling of the error of the stochastically evaluated three-point function with the lattice volume and find a favorable signal-to-noise ratio suggesting that our stochastic method can be used efficiently at large volumes to compute hadronic matrix elements.

hep-lat↗

arXiv2012

Application of Ewald's Method for Efficient Summation of Dyon Long-Range Potentials

We study a model of dyons for SU(2) Yang-Mills theory at finite temperature T < T_c, in particular its ability to generate a confining force between a static quark antiquark pair. The interaction between dyons corresponds to a long-range 1/r potential, which in naive treatments with a finite number of dyons typically gives rise to severe finite volume effects. To avoid such effects we apply the so-called Ewald method, which has its origin in solid state physics. The basic idea of Ewald's method is to consider a finite number of dyons inside a finite cubic volume and enforce periodicity of this volume. We explain the technicalities of Ewald's method and outline how the method can be applied to a wider class of 1/r^p long-range potentials.

hep-ph↗

arXiv2012

Sigma terms and strangeness content of the nucleon with $N_f=2+1+1$ twisted mass fermions

We study the nucleon matrix elements of the quark scalar-density operator using maximally twisted mass fermions with dynamical light ($u$,$d$), strange and charm degrees of freedom. We demonstrate that in this setup the nucleon matrix elements of the light and strange quark densities can be obtained with good statistical accuracy, while for the charm quark counterpart only a bound can be provided. The present calculation which is performed at only one value of the lattice spacing and pion mass serves as a benchmark for a future more systematic computation of the scalar quark content of the nucleon.

hep-lat↗

arXiv2011

Excited State Effects in Nucleon Matrix Element Calculations

We perform a high-statistics precision calculation of nucleon matrix elements using an open sink method allowing us to explore a wide range of sink-source time separations. In this way the influence of excited states of nucleon matrix elements can be studied. As particular examples we present results for the nucleon axial charge $g_A$ and for the first moment of the isovector unpolarized parton distribution $ _{u-d}$. In addition, we report on preliminary results using the generalized eigenvalue method for nucleon matrix elements. All calculations are performed using $N_f=2+1+1$ maximally twisted mass Wilson fermions.

hep-lat↗

arXiv2011

Dark matter Search and the Scalar Quark Contents of the Nucleon

We present lattice QCD simulation results from the European Twisted Mass Collaboration (ETMC) for the light, strange and charm quark contents of the nucleon. These quantities are important ingredients to estimate the cross-section for the detection of WIMPs as Dark Matter candidates. By employing a particular lattice QCD formulation, i.e. twisted mass fermions, accurate results of the light and strange scalar contents of the nucleon can be obtained. In addition, we provide a bound for the charm quark content of the nucleon.

hep-lat↗

arXiv2011

Confining dyon gas with finite-volume effects under control

As an approach to describe the long-range properties of non-Abelian gauge theories at non-zero temperature T < T_c, we consider a non-interacting ensemble of dyons (magnetic monopoles) with non-trivial holonomy. We show analytically, that the quark-antiquark free energy from the Polyakov loop correlator grows linearly with the distance, and how the string tension scales with the dyon density. In numerical treatments, the long-range tails of the dyon fields cause severe finite-volume effects. Therefore, we demonstrate the application of Ewald's summation method to this system. Finite-volume effects are shown to be under control, which is a crucial requirement for numerical studies of interacting dyon ensembles.

hep-ph↗

arXiv2011

Precision Study of Excited State Effects in Nucleon Matrix Elements

We present a dedicated analysis of the influence of excited states on the calculation of nucleon matrix elements. This calculation is performed at a fixed value of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, g_A, for which we use about 7,500 measurements, and on the average momentum of the unpolarized isovector parton distribution, _{u-d}, for which we use about 23,000 measurements. All computations are done employing N_f=2+1+1 maximally-twisted-mass Wilson fermions and using non-perturbatively calculated renormalization factors. Excited state effects are shown to be negligible for g_A whereas they lead to an O(10%) downward shift for _{u-d}.

hep-lat↗

arXiv2011

Nucleon matrix elements with $N_f=2+1+1$ maximally twisted fermions

We present the first lattice calculation of nucleon matrix elements using four dynamical flavors. We use the $N_f=2+1+1$ maximally twisted mass formulation. The renormalization is performed non-perturbatively in the RI$^\prime$-MOM scheme and results are given for the vector and axial vector operators with up to one-derivative. Our calculation of the average momentum of the unpolarized non-singlet parton distribution is presented and compared to our previous results obtained from the $N_f=2$ case.

hep-lat↗

arXiv2009

Cautionary remarks on the moduli space metric for multi-dyon simulations

We perform a detailed numerical investigation of the approximate moduli space metric proposed by Diakonov and Petrov [arXiv:0704.3181] for a confining model of dyons. Our findings strongly indicate that only for a small number of dyons at sufficiently low density this metric is positive definite - and, therefore, a valid moduli space metric - throughout a considerable part of configuration space. This poses strong limitations on results obtained by an unrestricted integration over collective coordinates in this model. It also indicates that strong correlations between collective coordinates will be essential for the physical content of a dyon model, which could be exhibited by a suitable simulation algorithm.

hep-ph↗