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## Publications

Publications (67)

This talk summarizes the progress made since Lattice 2021 in understanding and controlling the contributions of towers of multihadron excited states with mass gaps starting lower than of radial excitations, and in increasing our confidence in the extraction of ground state nucleon matrix elements. The most clear evidence for multihadron excited sta...

We present a high statistics study of the isovector nucleon charges and form factors using seven ensembles of 2+1-flavor Wilson-clover fermions. The axial vector and pseudoscalar form factors obtained on each of these ensembles satisfy the partially conserved axial current relation between them once the lowest energy Nπ excited state is included in...

The exponentially falling signal-to-noise ratio in all nucleon correlation functions, and the presence of towers of multihadron excited states with relatively small mass gaps makes extraction of matrix elements of various operators within the ground state nucleon challenging. Theoretically, the allowed positive parity states with the smallest mass...

We present our recent high precision calculations (Phys. Rev. D102 (2020) no.5, 054512 and JHEP 04 (2021) 044, JHEP 21 (2020) 004) of the first moment of nucleon isovector polarized, unpolarized and transversity distributions, i.e., momentum fraction, helicity and transversity moment, respectively. We use the standard method for the calculation of...

The fraction of the longitudinal momentum of He3 that is carried by the isovector combination of u and d quarks is determined using lattice QCD for the first time. The ratio of this combination to that in the constituent nucleons is found to be consistent with unity at the few-percent level from calculations with quark masses corresponding to mπ∼80...

The axial charge of the triton is investigated using lattice quantum chromodynamics (QCD). Extending previous work at heavier quark masses, calculations are performed using three ensembles of gauge field configurations generated with quark masses corresponding to a pion mass of 450 MeV and a single value of the lattice spacing. Finite-volume energy...

A bstract
A detailed analysis of the systematic uncertainties in the calculation of the isovector momentum fraction, 〈 x 〉 u − d , helicity moment, 〈 x 〉 Δ u − Δ d , and the transversity moment, 〈 x 〉 δu − δd , of the nucleon is presented using high-statistics data on seven ensembles of gauge configurations generated by the JLab/W&M/LANL/MIT collab...

The interactions between two octet baryons are studied at low energies using lattice quantum chromodynamics (LQCD) with larger-than-physical quark masses corresponding to a pion mass of mπ∼450 MeV and a kaon mass of mK∼596 MeV. The two-baryon systems that are analyzed range from strangeness S=0 to S=−4 and include the spin-singlet and triplet NN, Σ...

Systems with the quantum numbers of up to 12 charged and neutral pseudoscalar mesons, as well as one-, two-, and three-nucleon systems, are studied using dynamical lattice quantum chromodynamics and quantum electrodynamics (QCD+QED) calculations and effective field theory. QED effects on hadronic interactions are determined by comparing systems of...

We present a high statistics study of the isovector nucleon charges and form factors using seven ensembles of 2+1-flavor Wilson-clover fermions. The axial vector and pseudoscalar form factors obtained on including the lower energy $N \pi$ excited state in the spectral decomposition of correlation functions satisfy the partially conserved axial curr...

The axial charge of the triton is investigated using lattice quantum chromodynamics (QCD). Extending previous work at heavier quark masses, calculations are performed using three ensembles of gauge field configurations generated with quark masses corresponding to a pion mass of 450 MeV. Finite-volume energy levels for the triton, as well as for the...

High statistics results for the isovector momentum fraction, $\langle x \rangle_{u-d}$, helicity moment, $\langle x \rangle_{\Delta u-\Delta d}$, and the transversity moment, $\langle x\rangle_{\delta u-\delta d}$, of the nucleon are presented using seven ensembles of gauge configurations generated by the JLab/W&M/LANL/MIT collaborations using $2+1...

The interactions between two octet baryons are studied at low energies using lattice QCD (LQCD) with larger-than-physical quark masses corresponding to a pion mass of $m_{\pi}\sim 450$ MeV and a kaon mass of $m_{\pi}\sim 596$ MeV. The two-baryon systems that are analyzed range from strangeness $S=0$ to $S=-4$ and include the spin-singlet and triple...

The fraction of the longitudinal momentum of ${}^3\text{He}$ that is carried by the isovector combination of $u$ and $d$ quarks is determined using lattice QCD for the first time. The ratio of this combination to that in the constituent nucleons is found to be consistent with unity at the few-percent level from calculations with quark masses corres...

Systems with the quantum numbers of up to twelve charged and neutral pseudoscalar mesons, as well as one-, two-, and three-nucleon systems, are studied using dynamical lattice quantum chromodynamics and quantum electrodynamics (QCD+QED) calculations and effective field theory. QED effects on hadronic interactions are determined by comparing systems...

Complete flavor decompositions of the matrix elements of the scalar, axial, and tensor currents in the proton, deuteron, diproton, and He3 at SU(3)-symmetric values of the quark masses corresponding to a pion mass mπ∼806 MeV are determined using lattice quantum chromodynamics. At the physical quark masses, the scalar interactions constrain mean-fie...

Complete flavour decompositions of the scalar, axial and tensor charges of the proton, deuteron, diproton and $^3$He at SU(3)-symmetric values of the quark masses corresponding to a pion mass $m_\pi\sim806$ MeV are determined using lattice QCD. At the physical quark masses, the scalar charges constrain mean-field models of nuclei and the low-energy...

The role of gluons in the structure of the nucleon and light nuclei is investigated using lattice quantum chromodynamics (QCD) calculations. The first moment of the unpolarised gluon distribution is studied in nuclei up to atomic number $A=3$ at quark masses corresponding to pion masses of $m_\pi\sim 450$ and $806$ MeV. Nuclear modification of this...

Lattice quantum chromodynamics is used to constrain the interactions of two octet baryons at the SU(3) flavor-symmetric point, with quark masses that are heavier than those in nature (equal to that of the physical strange quark mass and corresponding to a pion mass of $\approx 806~\tt{MeV}$). Specifically, the S-wave scattering phase shifts of two-...

In this comment, we address a number of erroneous discussions and conclusions presented in the recent preprint arXiv:1703.07210. In particular, we show that lattice QCD determinations of bound states at quark masses corresponding to a pion mass of $m_\pi = 806$ MeV are robust, and that the extracted phases shifts for these systems pass all of the "...

A lattice quantum chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\to ppee\overline{\nu}_e\overline{\nu}_e$ transition is described in detail, expanding on the results presented in Ref. [1]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological det...

The potential importance of short-distance nuclear effects in double-$\beta$ decay is assessed using a lattice QCD calculation of the $nn\rightarrow pp$ transition and effective field theory methods. At the unphysical quark masses used in the numerical computation, these effects, encoded in the isotensor axial polarisability, are found to be of sim...

We present high-statistics estimates of the isovector charges of the nucleon from four 2+1-flavor ensembles generated using Wilson-clover fermions with stout smearing and tree-level tadpole improved Symanzik gauge action at lattice spacings $a=0.114$ and $0.080$ fm and with $M_\pi \approx 315$ and 200 MeV. The truncated solver method with bias corr...

I present results from the first lattice QCD calculations of axial-current matrix elements in light nuclei, performed by the NPLQCD collaboration. Precision calculations of these matrix elements, and the subsequent extraction of multi-nucleon axial-current operators, are essential in refining theoretical predictions of the proton-proton fusion cros...

The nuclear matrix element determining the $pp\to d e^+ \nu$ fusion cross section and the Gamow-Teller matrix element contributing to tritium $\beta$-decay are calculated with lattice Quantum Chromodynamics (QCD) for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3)-flavor-symmet...

We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.0...

Computing platforms equipped with accelerators like GPUs have proven to
provide great computational power. However, exploiting such platforms for
existing scientific applications is not a trivial task. Current GPU programming
frameworks such as CUDA C/C++ require low-level programming from the developer
in order to achieve high performance code. As...

Over the past years GPUs have been successfully applied to the task of
inverting the fermion matrix in lattice QCD calculations. Even strong scaling
to capability-level supercomputers, corresponding to O(100) GPUs or more has
been achieved. However strong scaling a whole gauge field generation algorithm
to this regim requires significantly more fun...

By introducing an additional operator into the action and using the
Feynman-Hellmann theorem we describe a method to determine both the quark line
connected and disconnected terms of matrix elements. As an illustration of the
method we calculate the gluon contribution (chromo-electric and chromo-magnetic
components) to the nucleon mass.

We present the first determination of charge symmetry violation (CSV) in the
spin-dependent parton distribution functions of the nucleon. This is done by
determining the first two Mellin moments of the spin-dependent parton
distribution functions of the octet baryons from N_f = 2 + 1 lattice
simulations. The results are compared with predictions fr...

QCD lattice simulations determine hadron masses as functions of the quark masses. From the gradients of these masses and using the Feynman-Hellmann theorem the hadron sigma terms can then be determined. We use here a novel approach of keeping the singlet quark mass constant in our simulations which upon using an SU(3) flavor symmetry breaking expan...

QPACE is a novel massively parallel architecture optimized for lattice QCD simulations. A single QPACE node is based on the IBM PowerXCell 8i processor. The nodes are interconnected by a custom 3-dimensional torus network implemented on an FPGA. The compute power of the processor is provided by 8 Synergistic Processing Units. Making effcient use of...

QCD lattice simulations yield hadron masses as functions of the quark masses.
From the gradients of the hadron masses the sigma terms can then be determined.
We consider here dynamical 2+1 flavour simulations, in which we start from a
point of the flavour symmetric line and then keep the singlet or average quark
mass fixed as we approach the physic...

Extensions to the C++ implementation of the QCD Data Parallel Interface are
provided enabling acceleration of expression evaluation on NVIDIA GPUs. Single
expressions are off-loaded to the device memory and execution domain leveraging
the Portable Expression Template Engine and using Just-in-Time compilation
techniques. Memory management is automat...

We calculate the disconnected contribution to the form factor for the
semileptonic decay of a D-meson into a final state, containing a flavor singlet
eta meson. We use QCDSF n_f=2+1 configurations at the flavor symmetric point
m_u=m_d=m_s and the partially quenched approximation for the relativistic charm
quark. Several acceleration and noise reduc...

QCD lattice simulations with 2+1 flavors (when two quark flavors are mass degenerate) typically start at rather large up-down and strange quark masses and extrapolate first the strange quark mass and then the up-down quark mass to its respective physical value. Here we discuss an alternative method of tuning the quark masses, in which the singlet q...

We study the spectra of heavy-light and heavy-heavy mesons containing charm
quarks, including higher spin states. We use two sets of $N_f = 2 + 1$ gauge
configurations, one set from QCDSF using the SLiNC action, and the other
configurations from the Budapest-Marseille-Wuppertal collaboration, using the
HEX smeared clover action. To extract informat...

We present a comprehensive analysis of the electromagnetic form factors of
the nucleon from a lattice simulation with two flavors of dynamical
O(a)-improved Wilson fermions. A key feature of our calculation is that we make
use of an extensive ensemble of lattice gauge field configurations with four
different lattice spacings, multiple volumes, and...

Graphic Processing Units (GPUs) are getting increasingly important as target
architectures in scientific High Performance Computing (HPC). NVIDIA
established CUDA as a parallel computing architecture controlling and making
use of the compute power of GPUs. CUDA provides sufficient support for C++
language elements to enable the Expression Template...

We present results from the QCDSF/UKQCD collaboration for the electromagnetic form factors, axial charges and momentum fractions for the hyperons. The simulations are performed on our new ensembles generated with 2+1 flavours of dynamical O(a)-improved Wilson fermions. A unique feature of these configurations is that the quark masses are tuned so t...

We report on recent results of the QCDSF/UKQCD Collaboration on
investigations of baryon structure using configurations generated with N_f=2+1
dynamical flavours of O(a) improved Wilson fermions. With the strange quark
mass as an additional dynamical degree of freedom in our simulations we avoid
the need for a partially quenched approximation when...

QCDSF–UKQCD Collaboration QCD lattice simulations with 2+1 flavours typically start at rather large up-down and strange quark masses and extrapolate first the strange quark mass to its physical value and then the up-down quark mass. An alternative method of tuning the quark masses is discussed here in which the singlet quark mass is kept fixed, whi...

We present results from the QCDSF/UKQCD collaboration for the electromagnetic
and semi-leptonic form factors for the hyperons. The simulations are performed
on our new ensembles generated with 2+1 flavours of dynamical O(a)-improved
Wilson fermions. A unique feature of these configurations is that the quark
masses are tuned so that the singlet quar...

We give an update on our ongoing efforts to compute the nucleon's form
factors and moments of structure functions using Nf=2 flavours of
non-perturbatively improved Clover fermions. We focus on new results obtained
on gauge configurations where the pseudo-scalar meson mass is in the range of
170-270 MeV. We will compare our results with various est...

By determining the quark momentum fractions of the octet baryons from N_f=2+1
lattice simulations, we are able to predict the degree of charge symmetry
violation in the parton distribution functions of the nucleon. This is of
importance, not only as a probe of our understanding of the non-perturbative
structure of the proton but also because such a...

QPACE is a novel massively parallel architecture optimized for lattice QCD simulations. Each node comprises an IBM PowerXCell 8i processor. The nodes are interconnected by a custom 3-dimensional torus network implemented on an FPGA. The architecture was systematically optimized with respect to power consumption. This put QPACE in the number one spo...

QPACE is a novel parallel computer which has been developed to be primarily used for lattice QCD simulations. The compute power is provided by the IBM PowerXCell 8i processor, an enhanced version of the Cell processor that is used in the Playstation 3. The QPACE nodes are interconnected by a custom, application optimized 3-dimensional torus network...

Application-driven computers for Lattice Gauge Theory simulations have often been based on system-on-chip designs, but the development costs can be prohibitive for academic project budgets. An alternative approach uses compute nodes based on a commercial processor tightly coupled to a custom-designed network processor. Preliminary analysis shows th...

We give an overview of the QPACE project, which is pursuing the development of a massively parallel, scalable supercomputer for LQCD. The machine is a three-dimensional torus of identical processing nodes, based on the PowerXCell 8i processor. The nodes are connected by an FPGA-based, application-optimized network processor attached to the PowerXCe...

The fractal structure of high-temperature graphs of the three-dimensional Ising and XY models is investigated by simulating these graphs directly on a cubic lattice and analyzing them with the help of percolation observables. The Ising graphs are shown to percolate right at the Curie critical point. The diverging length scale relevant to the graphs...

Contribution to a conf. proceeding (book/online)