Search results for "Computation"

Nucleon matrix elements from lattice QCD with all-mode-averaging and a domain-decomposed solver: An exploratory study

2017

We study the performance of all-mode-averaging (AMA) when used in conjunction with a locally deflated SAP-preconditioned solver, determining how to optimize the local block sizes and number of deflation fields in order to minimize the computational cost for a given level of overall statistical accuracy. We find that AMA enables a reduction of the statistical error on nucleon charges by a factor of around two at the same cost when compared to the standard method. As a demonstration, we compute the axial, scalar and tensor charges of the nucleon in $N_f=2$ lattice QCD with non-perturbatively O(a)-improved Wilson quarks, using O(10,000) measurements to pursue the signal out to source-sink sepa…

The Weak-Magnetic Moment of Heavy Quarks

1997

With initial and final particles on-shell, the anomalous weak-magnetic dipole moments of b and c quarks are electroweak gauge invariant quantities of the effective couplings Zb\bar{b} and Zc\bar{c}, respectively, and good candidates to test the Standard Model and/or new physics. Here we present a complete computation of these quantities within the Standard Model. We show that decoupling properties with respect to heavy particles do take place in the weak magnetic moment. The obtained values, a_b(M_Z^2)=(2.98-1.56i)x10^(-4) and a_c(M_Z^2)=(-2.80+1.09i)x10^(-5) are dominated by one-gluon exchange diagrams. The electroweak corrections are less than 1% of the total magnitude.

Calculating loops without loop calculations: Next-to-leading order computation of pentaquark correlators

2012

We compute next-to-leading order (NLO) perturbative QCD corrections to the correlators of interpolating pentaquark currents and their absorptive parts. We employ modular techniques in configuration space which saves us from the onus of having to do loop calculations. The modular technique is explained in some detail. We present explicit NLO results for several interpolating pentaquark currents that have been written down in the literature. Our modular approach is easily adapted to the case of NLO corrections to multiquark correlators with an arbitrary number of quarks/antiquarks.

Mathematical models on the way from superstring to photon

2002

Tomographic image of the proton

2016

We determine, based on the latest experimental Deep Virtual Compton Scattering experimental data, the dependence of the spatial size of the proton on the quark's longitudinal momentum. This results in a three-dimensional momentum-space image and tomography of the proton.

Quark Contraction Tool -- QCT

2016

We present a Mathematica package for the calculation of Wick contractions in quantum field theories - QCT. Furthermore the package aims at automatically generating code for the calculation of physical matrix elements, suitable for numerical evaluation in a C++ program. To that end commonly used algebraic manipulations for the calculation of matrix elements in lattice QCD are implemented.

The SCET_II and factorization

2003

We reformulate the soft-collinear effective theory which includes the collinear quark and soft gluons. The quark form factor is used to prove that SCET$_{\rm II}$ reproduces the IR physics of the full theory. We give a factorization proof in deep inelastic lepton-hadron scattering by use of the position space formulation.

Determination of m¯b/m¯c and m¯b from nf=4 lattice QCD+QED

2021

We extend HPQCD's earlier ${n}_{f}=2+1+1$ lattice-QCD analysis of the ratio of $\overline{\mathrm{MS}}$ masses of the $b$ and $c$ quark to include results from finer lattices (down to 0.03 fm) and a new calculation of QED contributions to the mass ratio. We find that ${\overline{m}}_{b}(\ensuremath{\mu})/{\overline{m}}_{c}(\ensuremath{\mu})=4.586(12)$ at renormalization scale $\ensuremath{\mu}=3\text{ }\text{ }\mathrm{GeV}$. This result is nonperturbative. Combining it with HPQCD's recent lattice $\mathrm{QCD}+\mathrm{QED}$ determination of ${\overline{m}}_{c}(3\text{ }\text{ }\mathrm{GeV})$ gives a new value for the $b$-quark mass: ${\overline{m}}_{b}(3\text{ }\text{ }\mathrm{GeV})=4.513(2…

Renormalization of the effective theory for heavy quarks at small velocity

1995

The slope of the Isgur-Wise function at the normalization point, $\xi^{(1)}(1)$,is one of the basic parameters for the extraction of the $CKM$ matrix element $V_{cb}$ from exclusive semileptonic decay data. A method for measuring this parameter on the lattice is the effective theory for heavy quarks at small velocity $v$. This theory is a variant of the heavy quark effective theory in which the motion of the quark is treated as a perturbation. In this work we study the lattice renormalization of the slow heavy quark effective theory. We show that the renormalization of $\xi^{(1)}(1)$ is not affected by ultraviolet power divergences, implying no need of difficult non-perturbative subtraction…

Kaon mixing beyond the SM from N-f=2 tmQCD and model independent constraints from the UTA

2013

We present the first unquenched, continuum limit, lattice QCD results for the matrix elements of the operators describing neutral kaon oscillations in extensions of the Standard Model. Owing to the accuracy of our calculation on Delta S = 2 weak Hamiltonian matrix elements, we are able to provide a refined Unitarity Triangle analysis improving the bounds coming from model independent constraints on New Physics. In our non-perturbative computation we use a combination of N-f = 2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks in order to achieve both O(a)-improvement and continuum-like renormalization properties for the relevant four-fermion operators. The calculation of t…