Two nucleons on a lattice (original) (raw)

Two nucleon systems atmπ∼450 MeVfrom lattice QCD

Physical Review D, 2015

Nucleon-nucleon systems are studied with lattice quantum chromodynamics at a pion mass of m π ∼ 450 MeV in three spatial volumes using n f = 2 + 1 flavors of light quarks. At the quark masses employed in this work, the deuteron binding energy is calculated to be B d = 14.4 +3.2 −2.6 MeV, while the dineutron is bound by B nn = 12.5 +3.0 −5.0 MeV. Over the range of energies that are studied, the S-wave scattering phase shifts calculated in the 1 S 0 and 3 S 1-3 D 1 channels are found to be similar to those in nature, and indicate repulsive shortrange components of the interactions, consistent with phenomenological nucleon-nucleon interactions. In both channels, the phase shifts are determined at three energies that lie within the radius of convergence of the effective range expansion, allowing for constraints to be placed on the inverse scattering lengths and effective ranges. The extracted phase shifts allow for matching to nuclear effective field theories, from which low energy counterterms are extracted and issues of convergence are investigated. As part of the analysis, a detailed investigation of the single hadron sector is performed, enabling a precise determination of the violation of the Gell-Mann-Okubo mass relation.

Nucleon-Nucleon Scattering from Fully Dynamical Lattice QCD

Physical Review Letters, 2006

We present results of the first fully-dynamical lattice QCD determination of hyperon-nucleon scattering. One s-wave phase shift was determined for nΛ scattering in both spin-channels at pion masses of 350, 490, and 590 MeV, and for nΣ − scattering in both spin channels at pion masses of 490, and 590 MeV. The calculations were performed with domain-wall valence quarks on dynamical, staggered gauge configurations with a lattice spacing of b ∼ 0.125 fm.

Nucleon Structure from Lattice QCD Using a Nearly Physical

2012

We report the first Lattice QCD calculation using the almost physical pion mass mpi=149 MeV that agrees with experiment for four fundamental isovector observables characterizing the gross structure of the nucleon: the Dirac and Pauli radii, the magnetic moment, and the quark momentum fraction. The key to this success is the combination of using a nearly physical pion mass and excluding the contributions of excited states. An analogous calculation of the nucleon axial charge governing beta decay has inconsistencies indicating a source of bias at low pion masses not present for the other observables and yields a result that disagrees with experiment.

Exploring the nucleon structure from first principles of QCD

Journal of Physics: Conference Series, 2010

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions.

Spectra and scattering of light lattice nuclei from effective field theory

Physical Review C, 2015

The vast number of phenomena of the nuclear chart depend on a relatively small set of quantum chromodynamics (QCD) parameters -in the low energies relevant for nuclear physics, a mass scale M QCD associated to the strong coupling constant, the masses m q of the two lightest quarks, the electromagnetic coupling strength, and the vacuum angle. Lattice QCD (LQCD) is a numerical framework which enables us, at least in principle, to relate nuclear and QCD parameters, once effects due to finite lattice spacing and size are removed. The last few years have witnessed significant progress in predicting the properties of light nuclei with nucleon number A ≤ 4, but at relatively large quark masses and neglecting time-reversal and isospin violation. (See Ref.

A variational study of two-nucleon systems with lattice QCD

arXiv (Cornell University), 2021

The low-energy spectrum and scattering of two-nucleon systems are studied with lattice quantum chromodynamics using a variational approach. A wide range of interpolating operators are used: dibaryon operators built from products of planewave nucleons, hexaquark operators built from six localized quarks, and quasi-local operators inspired by two-nucleon bound-state wavefunctions in low-energy effective theories. Sparsening techniques are used to compute the timeslice-to-all quark propagators required to form correlation-function matrices using products of these operators. Projection of these matrices onto irreducible representations of the cubic group, including spin-orbit coupling, is detailed. Variational methods are applied to constrain the low-energy spectra of two-nucleon systems in a single finite volume with quark masses corresponding to a pion mass of 806 MeV. Results for Sand D-wave phase shifts in the isospin singlet and triplet channels are obtained under the assumption that partial-wave mixing is negligible. Tests of interpolatingoperator dependence are used to investigate the reliability of the energy spectra obtained and highlight both the strengths and weaknesses of variational methods. These studies and comparisons to previous studies using the same gauge-field ensemble demonstrate that interpolating-operator dependence can lead to significant effects on the two-nucleon energy spectra obtained using both variational and nonvariational methods, including missing energy levels and other discrepancies. While this study is inconclusive regarding the presence of two-nucleon bound states at this quark mass, it provides robust upper bounds on two-nucleon energy levels that can be improved in future calculations using additional interpolating operators and is therefore a step toward reliable nuclear spectroscopy from the underlying Standard Model of particle physics.

Probing nucleon structure on the lattice

European Physical Journal A, 2007

The QCDSF/UKQCD Collaboration has an ongoing program to calculate nucleon matrix elements with two flavours of dynamical O(a) improved Wilson fermions. Here we present recent results on the electromagnetic form factors, the quark momentum fraction 〈x〉 and the first three moments of the nucleon's spin-averaged and spin-dependent generalised parton distributions, including preliminary results with pion masses as low as 320MeV.

Hyperon–nucleon scattering from fully-dynamical lattice QCD

Nuclear Physics A, 2007

Progress towards a lattice determination of (moments of) nucleon structure functions

Nuclear Physics B - Proceedings Supplements, 2002

Using unimproved and non-perturbatively O(a) improved Wilson fermions, results are given for the three lowest moments of unpolarised nucleon structure functions. Renormalisation, chiral extrapolation and the continuum limit of the matrix elements are briefly discussed. The simulations are performed for both quenched and two flavours of unquenched fermions. No obvious sign of deviation from linearity in the chiral extrapolations are found. (This is most clearly seen in our quenched unimproved data, which extends to lighter quark mass.) Possible quenching effects also seem to be small. The lowest moment thus remains too large, so it seems to be necessary to reach smaller quark masses in numerical simulations.

Effective Field Theory for Lattice Nuclei

Physical Review Letters, 2015

We show how nuclear effective field theory (EFT) and ab initio nuclear-structure methods can turn input from lattice quantum chromodynamics (LQCD) into predictions for the properties of nuclei. We argue that pionless EFT is the appropriate theory to describe the light nuclei obtained in recent LQCD simulations carried out at pion masses much heavier than the physical pion mass. We solve the EFT using the effective-interaction hyperspherical harmonics and auxiliary-field diffusion Monte Carlo methods. Fitting the three leading-order EFT parameters to the deuteron, dineutron and triton LQCD energies at mπ ≈ 800 MeV, we reproduce the corresponding alpha-particle binding and predict the binding energies of mass-5 and 6 ground states.

Two nucleons on a lattice (original) (raw)

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