In a recent study of the $\mathrm{\ensuremath{\Lambda}}(1405)$ the suppression of the strange-quark contribution to the magnetic form factor was interpreted as the discovery of a dominant antikaon-nucleon composition for this low-lying state. We confirm this result by calculating the light $u$ and $d$ quark contributions to the $\mathrm{\ensuremath{\Lambda}}(1405)$ magnetic form factor in lattice QCD in order to determine the extent to which their contributions support this exotic molecular description. Drawing on the recent graded-symmetry approach for the flavor-singlet components of the $\mathrm{\ensuremath{\Lambda}}(1405)$, the separation of connected and disconnected contributions is performed in both the flavor-octet and -singlet representations. In both cases, the disconnected-loop contributions are found to be large. The relationship between light-quark contributions to the $\mathrm{\ensuremath{\Lambda}}(1405)$ magnetic form factor and the connected contributions of the nucleon magnetic form factors is established and compared with lattice calculations of the same quantities, confirming the $\overline{K}N$ molecular structure of the $\mathrm{\ensuremath{\Lambda}}(1405)$ in lattice QCD.

The light-quark sector of the Lambda(1405) baryon is examined in the context of the recent discovery of a dominant antikaon-nucleon composition at low quark masses. Further evidence for this interpretation of the Lambda(1405) is presented, by calculating the u and d quark contributions to the Lambda(1405) magnetic form factors in lattice QCD. The extent to which these quantities are consistent with the exotic molecular description can then be quantified by comparing the results with the equivalent nucleon form factors. Drawing on a recent extension of the graded-symmetry approach for the flavor-singlet components of the Lambda(1405), the separation of the connected and disconnected contributions is performed in both the flavor-octet and singlet representations. In both cases, the disconnected loop contributions are found to be unexpectedly large. The relationship between the light-quark contributions to the Lambda(1405) magnetic form factor and the connected contributions of the nucleon magnetic form factors is thus confirmed in the case of lattice QCD, establishing compelling evidence for a KN molecular structure of the Lambda(1405) near the physical point.

With the widespread adoption of cloud computing, high-performance computing (HPC) is no longer limited to organisations with the funds and manpower necessary to house and run a supercomputer. However, the performance of large-scale scientific applications in the cloud has in the past been constrained by latency and bandwidth. The main reasons for these constraints are the design decisions of cloud providers, primarily focusing on high-density applications such as web services and data hosting.In this paper, we provide an overview of a high performance OpenStack cloud implementation at the National Computational Infrastructure (NCI). This cloud is targeted at high-performance scientific applications, and enables scientists to build their own clusters when their demands and software stacks conflict with traditional bare-metal HPC environments. In this paper, we present the architecture of our 56 GbE cloud and a preliminary set of HPC benchmark results against the more traditional cloud and native InfiniBand HPC environments.Three different network interconnects and configurations were tested as part of the Cloud deployment. These were 10G Ethernet, 56G Fat-tree Ethernet and native FDR Full Fat-tree InfiniBand (IB). In this paper, these three solutions are discussed from the viewpoint of on-demand HPC clusters focusing on bandwidth, latency and security. A detailed analysis of these metrics in the context of micro-benchmarks and scientific applications is presented, including the affects of using TCP and RDMA on scientific applications. (C) 2016 The Authors. Published by Elsevier B.V.

Jonathan M. M. Halla, Waseem Kamleh∗a†, Derek B. Leinwebera, Benjamin J. Menaduea,b, Benjamin J. Owena, Anthony W. Thomasa,c, Ross D. Younga,c a Special Research Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, South Australia 5005, Australia b National Computational Infrastructure (NCI), Australian National University, Australian Capital Territory 0200, Australia c ARC Centre of Excellence for Particle Physics at the Terascale (CoEPP), Department of Physics, University of Adelaide, South Australia 5005, Australia

We review recent lattice QCD results from the CSSM using the variational method to isolate the Λ(1405) and explore its structure.The behaviour of the electric and magnetic form factors as the up and down quark masses approach their physical values, together with a Hamiltonian effectivefield-theory model analysis of the lattice QCD energy levels, reveal that the structure is dominated by a bound antikaon-nucleon component [1].

Here we present preliminary results for the evaluation of the electromagnetic form factors for the lowest-lying negative-parity, spin-$\frac{1}{2}$ nucleons, namely the $S_{11}(1535)$ and $S_{11}(1650)$, through the use of the variational method. We find that the characteristics of the electric form factor, $G_{E}$, are similar between these states, however significant differences are observed between the quark-sector contributions to the magnetic form factor, $G_{M}$. Within simple constituent quark models, these states are understood to be admixtures of $s=\frac{1}{2}$ and $s=\frac{3}{2}$ states coupled to orbital angular momentum $\ell = 1$. Our results reveal a qualitative difference in the manner in which the singly-represented quark sector contributes to these baryon magnetic form factors.

With the ongoing experimental interest in exploring the excited hadron spectrum, evaluations of the matrix elements describing the formation and decay of such states via radiative processes provide us with an important connection between theory and experiment. In particular, determinations obtained via the lattice allow for a direct comparison of QCD-expectation with experimental observation. Here we present the first light quark determination of the ρ→πγ transition form factor from lattice QCD using dynamical quarks. Using the PACS-CS 2+1 flavour QCD ensembles we are able to obtain results across a range of masses, to the near physical value of m_π = 157 MeV. An important aspect of our approach is the use of variational methods to isolate the desired QCD eigenstate. For low-lying states, such techniques facilitate the removal of excited state contributions. In principle the method enables one to consider arbitrary eigenstates. We find our results are in accord with the non-relativistic quark model for heavy masses. In moving towards the light-quark regime we observe an interesting quark mass dependence, contrary to the quark model expectation. Comparison of our light-quark result with experimental determinations highlights a significant discrepancy suggesting that disconnected sea-quark loop contributions may play a significant role in fully describing this process.

For almost 50 years the structure of the Λ(1405) resonance has been a mystery. Even though it contains a heavy strange quark and has odd parity, its mass is lower than any other excited spin-1/2 baryon. Dalitz and co-workers speculated that it might be a molecular state of an antikaon bound to a nucleon. However, a standard quark-model structure is also admissible. Although the intervening years have seen considerable effort, there has been no convincing resolution. Here we present a new lattice QCD simulation showing that the strange magnetic form factor of the Λ(1405) vanishes, signaling the formation of an antikaon-nucleon molecule. Together with a Hamiltonian effective-field-theory model analysis of the lattice QCD energy levels, this strongly suggests that the structure is dominated by a bound antikaon-nucleon component. This result clarifies that not all states occurring in nature can be described within a simple quark model framework and points to the existence of exotic molecular meson-nucleon bound states.

In recent years, the use of variational analysis techniques in lattice QCD has been demonstrated to be successful in the investigation of the rest-mass spectrum of many hadrons. However, due to parity-mixing, more care must be taken for investigations of boosted states to ensure that the projected correlation functions provided by the variational analysis correspond to the same states at zero momentum. In this paper we present the Parity-Expanded Variational Analysis (PEVA) technique, a novel method for ensuring the successful and consistent isolation of boosted baryons through a parity expansion of the operator basis used to construct the correlation matrix.

With the ongoing experimental interest in exploring the excited hadron spectrum, evaluations of the matrix elements describing the formation and decay of such states via radiative processes provide us with an important connection between theory and experiment. In particular, determinations obtained via the lattice allow for a direct comparison of QCD-expectation with experimental observation. Here we present the first light quark determination of the $ρ\rightarrow πγ$ transition form factor from lattice QCD using dynamical quarks. Using the PACS-CS 2+1 flavour QCD ensembles we are able to obtain results across a range of masses, to the near physical value of $m_π= 157$ MeV. An important aspect of our approach is the use of variational methods to isolate the desired QCD eigenstate. For low-lying states, such techniques facilitate the removal of excited state contributions. In principle the method enables one to consider arbitrary eigenstates. We find our results are in accord with the non-relativistic quark model for heavy masses. In moving towards the light-quark regime we observe an interesting quark mass dependence, contrary to the quark model expectation. Comparison of our light-quark result with experimental determinations highlights a significant discrepancy suggesting that disconnected sea-quark loop contributions may play a significant role in fully describing this process.

The ability for most hadrons to decay via strong interactions prevents the direct measurement of their electromagnetic properties. However, a detailed understanding of how these resonant states feature in scattering processes can allow one to disentangle such information from photo production processes. In particular, there has been increasing interest in the determination of magnetic dipole moments using such methods. In a recent study [1], Gudino et al. provide the first experimental determination of the magnetic dipole moment of the rho meson. To facilitate a comparison with this experimental determination, we present a calculation of the rho meson and pion electromagnetic form factors calculated in the framework of lattice QCD. Using the PACS-CS 2 + 1 flavor full QCD gauge field configurations, we are able to access low Q(2) values at near-physical quark masses. Through the use of variational techniques, we control excited state systematics in the matrix elements of the lowest-lying states and gain access to the matrix elements of the first excited state. Our determination of the rho meson g-factor g(rho) = 2.21(8) is in excellent agreement with this experimental determination, but with a significantly smaller uncertainty.

For almost 50 years the structure of the Lambda 1405 resonance has been a mystery. Recently, a new lattice QCD simulation showing that its strange magnetic form factor vanishes, together with a comprehensive Hamiltonian analysis of the lattice QCD energy levels, has unambiguously established that the structure is dominated by a bound anti-kaon--nucleon component [1]. Here we present supplementary information for Ref. [1] including a presentation of the relevant Hamiltonian effective field theory and an illustration of the volume dependence of the results and their connection to the infinite volume limit of Nature.

We present a first look at the application of variational techniques for the extraction of the electromagnetic properties of an excited nucleon system. In particular, we include preliminary results for charge radii and magnetic moments of the proton, its first even-parity excitation and the Δ^+.

Building on our successful technique to isolate the otherwise-elusive $\Lambda$(1405) using correlation matrix techniques and multiple source and sink smearings, we present calculations of the quark sector contributions to the electric form factors of the $\Lambda$(1405). Using the PACS-CS $(2+1)$-flavour full-QCD ensembles available through the ILDG, our calculations reveal behaviour consistent with the development of a non-trivial molecular $\overline{K}N$ bound-state component as one approaches the physical values of the $u$ and $d$ quark masses.

Building on our successful technique to isolate the otherwise-elusive Λ(1405) using correlation matrix techniques and multiple source and sink smearings, we present calculations of the quark sector contributions to the electric form factors of the Λ(1405). Using the PACS-CS (2+ 1)flavour full-QCD ensembles available through the ILDG, our calculations reveal behaviour consistent with the development of a non-trivial molecular KN bound-state component as one approaches the physical values of the u and d quark masses.

A long standing problem in lattice QCD has been the discrepancy between the experimental and calculated values for the axial charge of the nucleon, gA≡GA(Q2=0). Though finite volume effects have been shown to be large, it has also been suggested that excited state effects may also play a significant role in suppressing the value of gA. In this work, we apply a variational method to generate operators that couple predominantly to the ground state, thus systematically removing excited state contamination from the extraction of gA. The utility and success of this approach is manifest in the early onset of ground state saturation and the early onset of a clear plateau in the correlation function ratio proportional to gA. Through a comparison with results obtained via traditional methods, we show how excited state effects can suppress gA by as much as 8% if sources are not properly tuned or source–sink separations are insufficiently large.

Two measures are defined to evaluate the coupling strength of smeared interpolating operators to hadronic states at a variety of momenta. Of particular interest is the extent to which strong overlap can be obtained with individual high-momentum states. This is vital to exploring hadronic structure at high momentum transfers on the lattice and addressing interesting phenomena observed experimentally. We consider a novel idea of altering the shape of the smeared operator to match the Lorentz contraction of the probability distribution of the high-momentum state, and show a reduction in the relative error of the two-point function by employing this technique. Our most important finding is that the overlap of the states becomes very sharp in the smearing parameters at high momenta and fine tuning is required to ensure strong overlap with these states.

The odd-parity ground state of the Λ baryon lies surprisingly low in mass. At 1405 MeV, it lies lower than the odd-parity ground-state nucleon, even though it has a valence strange quark. Using the PACS-CS (2+1)-flavor full-QCD ensembles, we employ a variational analysis using source and sink smearing to isolate this elusive state. For the first time we reproduce the correct level ordering with respect to nearby scattering thresholds. With a partially quenched strange quark to produce the appropriate kaon mass, we find a low-lying, odd-parity mass trend consistent with the experimental value.

We review recent results for baryon properties from lattice QCD arising from the CSSM Lattice Collaboration. Resonance physics is of particular interest. We explore both the positive parity nucleon spectrum, including the N(1440) Roper state, and the negative parity Λ spectrum, which contains the low-lying Λ(1405). The electromagnetic properties of baryons are also of key interest, and we review the status of our calculations of the neutron magnetic moment obtained by measuring the reponse of the neutron to a uniform background field.