Efficient operators for studying higher partial waves

An extended multi-hadron operator is developed to extract the spectra of irreducible representations in the finite volume. The irreducible representations of the cubic group are projected using a coordinate-space operator. The correlation function of this operator is computationally efficient to extract lattice spectra. In particular, this new formulation only requires propagator inversions from two distinct locations, at fixed physical separation. We perform a proof-of-principle study on a $24^3 \times 48$ lattice volume with $m_\pi\approx 900$~MeV by isolating the spectra of $A^+_1$, $E^+$ and $T^+_2$ of the $\pi\pi$ system with isospin-2 in the rest frame.Comment: 8 pages, 3 figures, Contribution to the conference Lattice201

The FLIC Overlap Quark Propagator

FLIC overlap fermions are a variant of the standard (Wilson) overlap action, with the FLIC (Fat Link Irrelevant Clover) action as the overlap kernel rather than the Wilson action. The structure of the FLIC overlap fermion propagator in momentum space is studied, and a comparison against previous studies of the Wilson overlap propagator in quenched QCD is performed. To explore the scaling properties of the propagator for the two actions, numerical calculations are performed in Landau Gauge across three lattices with different lattice spacing $a$ and similar physical volumes. We find that at light quark masses the acti ons agree in both the infrared and the ultraviolet, but at heavier masses some disagreement in the ultraviolet appears. This is attributed to the two action s having different discretisation errors with the FLIC overlap providing superior performance in this regime. Both actions scale reasonably, but some scaling violations are observed

Instanton contributions to the low-lying hadron mass spectrum

The role of instanton-like objects in the QCD vacuum on the mass spectrum of low-lying light hadrons is explored in lattice QCD. Using over-improved stout-link smearing, tuned to preserve instanton-like objects in the QCD vacuum, the evolution of the mass spectrum under smearing is examined. The calculation is performed using a $20^3\times40$ dynamical fat-link-irrelevant-clover (FLIC) fermion action ensemble with lattice spacing 0.126 fm. Through the consideration of a range of pion masses, the effect of the vacuum instanton content is compared at a common pion mass. While the qualitative features of ground-state hadrons are preserved on instanton-dominated configurations, the excitation spectrum experiences significant changes. The underlying physics revealed shows little similarity to the direct-instanton interaction predictions of the instanton liquid model.Comment: 11 pages, 17 figure

Quantifying the Risk of Wildfire Ignition by Power Lines under Extreme Weather Conditions

Utilities in California conduct Public Safety Power Shut-offs (PSPSs) to eliminate the elevated chances of wildfire ignitions caused by power lines during extreme weather conditions. We propose Wildfire Risk Aware operation planning Problem (WRAP), which enables system operators to pinpoint the segments of the network that should be de-energized. Sustained wind and wind gust can lead to conductor clashing, which could ignite surrounding vegetation. The 3D non-linear vibration equations of power lines are employed to generate a dataset that considers physical, structural, and meteorological parameters. With the help of machine learning techniques, a surrogate model is obtained which quantifies the risk of wildfire ignition by individual power lines under extreme weather conditions. The cases illustrate the superior performance of WRAP under extreme weather conditions in mitigating wildfire risk and serving customers compared to the naive PSPS approach and another method in the literature. Cases are also designated to sensitivity analysis of WRAP to critical load-serving control parameters in different weather conditions. Finally, a discussion is provided to explore our wildfire risk monetization approach and its implications for WRAP decisions

Lattice QCD Evidence that the Lambda(1405) Resonance is an Antikaon-Nucleon Molecule

For almost 50 years the structure of the Lambda(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 Lambda(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.Comment: Manuscript accepted for publication. 4 figures, 5 page

Improved determination of hadron matrix elements using the variational method

The extraction of hadron form factors in lattice QCD using the standard two- and three-point correlator functions has its limitations. One of the most commonly studied sources of systematic error is excited state contamination, which occurs when correlators are contaminated with results from higher energy excitations. We apply the variational method to calculate the axial vector current gA and compare the results to the more commonly used summation and two-exponential fit methods. The results demonstrate that the variational approach offers a more efficient and robust method for the determination of nucleon matrix elements.Comment: 7 pages, 6 figures, talk presented at Lattice 2015, PoS (LATTICE2015

Model reduction in computational homogenization for transient heat conduction

International audienceThis paper presents a computationally efficient homogenization method for transient heat conduction problems. The notion of relaxed separation of scales is introduced and the homogenization framework is derived. Under the assumptions of linearity and relaxed separation of scales, the microscopic solution is decomposed into a steady-state and a transient part. Static condensation is performed to obtain the global basis for the steady-state response and an eigenvalue problem is solved to obtain a global basis for the transient response. The macroscopic quantities are then extracted by averaging and expressed in terms of the coefficients of the reduced basis. Proof-of-principle simulations are conducted with materials exhibiting high contrast material properties. The proposed homogenization method is compared with the conventional steady-state homogenization and transient computational homogenization methods. Within its applicability limits, the proposed homogenization method is able to accurately capture the microscopic thermal inertial effects with significant computational efficiency

Genetic diversity of bacterial wilt caused by <i>Ralstonia solanacearum</i> as assessed by PCR

The current research was conducted to investigate genetic diversity of Ralstonia solanacearum for comparison of different strains that were collected mainly from Netherlands as well as from Bangladesh, Brazil, Kenya, Egypt, Pakistan and Palma. Forty six strains were included in contemporary studies whereas main biovars for these strains included biovar-2 except GMI1000 that belonged to biovar 3. Genetic diversity of bacterial wilt disease caused by R. solancearum was assessed by focusing mainly on three genes i.e. mutL, cbhA and dps. All the genes seem to be conserved but in case of mutL some strains showed divergence. Multi Locus Sequence Typing (MLST) scheme was used in this contemporary research. It was concluded that polymerized chain reaction (PCR) is the most imperative and appropriate modern tool of molecular biology to find genetic diversity in Ralstonia solanacearum causing bacterial wilt