Light hadrons with improved staggered quarks: Approaching the continuum limit

We present results for the static interquark potential, lightest glueballs, light hadron spectrum, and topological susceptibility using a nonperturbatively improved action on a ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units (\ensuremath{\sim}1.7 fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavors of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ${(M}_{\mathrm{PS}}{/M}_{V}>~0.58,$ where PS denotes pseudoscalar and $V$ denotes vector). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.

A comparison is made of the (quenched) light hadron spectrum and of simple matrix elements for a hypercubic fermion action (based on a fixed point action) and the clover action, both using fat links, at a lattice spacing a= 0.18 fm. Renormalization constants for the naive and improved vector current and the naive axial current are computed using Ward identities. The renormalization factors are very close to unity, and the spectroscopy of light hadrons and the pseudoscalar and vector decay constants agree well with simulations at smaller lattice spacings (and with experiment).

Through the embedding of superconformal quantum mechanics into AdS space, it is possible to construct an effective supersymmetric QCD light-front Hamiltonian for hadrons, which includes a spin-spin interaction between the hadronic constituents. A specific breaking of conformal symmetry determines a unique effective quark-confining potential for light hadrons, as well as remarkable connections between the meson, baryon, and tetraquark spectra. The pion is massless in the chiral limit and has no supersymmetric partner. The excitation spectra of relativistic light-quark meson, baryon and tetraquark bound states lie on linear Regge trajectories with identical slopes in the radial and orbital quantum numbers. Although conformal symmetry is strongly broken by the heavy quark mass, the basic underlying supersymmetric mechanism, which transforms mesons to baryons (and baryons to tetraquarks) into each other, still holds and gives remarkable connections across the entire spectrum of light, heavy-light and double-heavy hadrons. Here we show that all the observed hadrons can be related through this effective supersymmetric QCD, and that it can be used to identify the structure of the new charmonium states.

Light hadron spectrum and light quark masses from lattice QCD

Light hadron spectrum — MILC results with the Kogut-Susskind and Wilson actions

Deriving the light hadron spectrum from first principles of QCD has been a fundamental issue in elementary particle physics since the mid-1970s, when QCD was established. With this goal in mind, we have carried out large-scale simulations of lattice QCD on the CPPACS computer. In this article, we present results for the light hadron spectrum derived in the quenched approximation to lattice QCD. We find that although the global structure of the observed spectrum is reproduced, the quenched spectrum systematically deviates from experiment when examined with an accuracy at better than a 10% level. Results for light quark masses are also reported. Another simulation of full QCD done recently (also on the CP-PACS computer) shows indications that the discrepancy observed in quenched QCD is significantly reduced by the introduction of two flavors of light dynamical quarks.

We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at $\beta = 5.6$ on a $16^3 \times 32$ lattice. Four sets of sea quark masses corresponding to the range $.69 \leq m_\pi/m_\rho \leq .83$ are investigated. For reference we also ran a quenched simulation at $\beta_{\sf eff} = 6.0$, which is the point of equal lattice spacing, $a_{\rho}^{-1}$. In the light sector, we find the chiral extrapolation to physical u- and d- masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the $N_F = 2$ approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical $K-K^*$ splitting.

We construct high order symmetric volume-preserving methods for the relativistic dynamics of a charged particle by the splitting technique with processing. By expanding the phase space to include the time t, we give a more general construction of volume-preserving methods that can be applied to systems with time-dependent electromagnetic fields. The newly derived methods provide numerical solutions with good accuracy and conservative properties over long time of simulation. Furthermore, because of the use of an accuracy-enhancing processing technique, the explicit methods obtain high-order accuracy and are more efficient than the methods derived from standard compositions. The results are verified by the numerical experiments. Linear stability analysis of the methods shows that the high order processed method allows larger time step size in numerical integrations.

Hadron masses in lattice QCD

Light hadron spectrum with two flavors of O(a) improved dynamical quarks: final results from JLQCD

In numerical integration, the integral function often encountered in some parts of the curve of rapid change than other parts, then use adaptive integration to solve. In this paper, adaptive five-point Boolean integration method, the theoretical formula is derived and the corresponding error estimation formula. This method is flexible and can automatically adjust the step length, deal with rapid change, curve, gentle conditions, so that the results meet the accuracy requirements. Finally, an example of how to use adaptive integration method, compared to the adaptive Boolean three five-point Simpson integral formula with the calculated results, concluded that the former is greatly superior to the latter.

We present results for the static interquark potential, light meson and baryon masses, and light pseudoscalar meson decay constants obtained from simulations of domain wall QCD with one dynamical flavour approximating the s quark, and two degenerate dynamical flavours with input bare masses ranging from m{sub s} to m{sub s}/4 approximating the u and d quarks. We compare these quantities obtained using the Iwasaki and DBW2 improved gauge actions, and actions with larger rectangle coefficients, on 16{sup 3}x32 lattices. We seek parameter values at which both the chiral symmetry breaking residual mass due to the finite lattice extent in the fifth dimension and the Monte Carlo time history for topological charge are acceptable for this set of quark masses at lattice spacings above 0.1 fm. We find that the Iwasaki gauge action is best, demonstrating the feasibility of using QCDOC to generate ensembles which are good representations of the QCD path integral on lattices of up to 3 fm in spatial extent with lattice spacings in the range 0.09-0.13 fm. Despite large residual masses and a limited number of sea quark-mass values with which to perform chiral extrapolations, our results for light hadronic physics scale and agree with experimental measurementsmore » within our statistical uncertainties.« less

This paper describes a methodology for estimating the numerical errors in real-time simulation based on comparing two real-time simulations, one with the nominal integration step size and the second with an augmented step size. Accurate interpolation formulas are then used to convert the outputs from the second simulation to outputs at the discrete times for the first simulation. This permits a direct computation of the difference between the two simulations at common discrete times. Assuming that the dynamic errors vary as hk, where h is the integration step size and k is known, a simple formula can then be used to calculate the deviation of either simulation from the solution for zero step size. While only approximate, this procedure results in dynamic error estimates that are surprisingly accurate, as demonstrated in the paper in example simulations that use both single and multi-rate integrations. It turns out that three simulations, each with a different integration step size, can be used to estimate the exponent k in the dependence of dynamic errors on hk. This in turn allows programming errors, such as the inadvertent introduction of a one-frame delay within the simulation code, to be identified. The author feels that the methodology described in the paper can play a major role in optimizing as well as verifying the dynamic fidelity of real-time, hardware-in-the-loop simulations.

The mixed-potential integral-equation approach, using spatial-domain closed-form Green's functions, and discretized with the method-of-moments, is a state-of-the-art method for the analysis of planar microstrip circuits. One of its most time-demanding tasks is the evaluation of the impedance matrix terms, which typically requires the numerical computation of two-dimensional integrals. A method based on suitable changes of coordinates and domains is introduced in this paper in order to reduce such integrals to a quasi-one-dimensional numerical integration, with a substantial enhancement in the efficiency of the analysis, without affecting the accuracy of the approach. Results are given demonstrating, for practical accuracy values, an improvement of typically one order of magnitude in simulation times.

This paper describes two novel methods for distributed simulation of nonlinear power system dynamics, which are named two-level integration and interaction-level integration. An underlying assumption is that the simulation of dynamic response is distributed spatially, i.e. each power system component and/or each group of components perform numerical integration of their own states while occasionally communicating relevant information with their neighbors. The novelty of the proposed methods is in exploiting the structure of dynamic equations of typical power system components to shorten the total simulation time in this distributed setting. The proposed methods consist of a number of state transformations on the dynamical power system model which bring this model into a form favored for distributed numerical integration. These transformations, proposed first in [1] and [2] for control design, separate internal component dynamics from dynamics of its interactions with neighboring components. It is further shown on a simple example that it is sufficient to exchange the information between components at a rate determined by the dynamics of the interaction variables to successfully perform numerical integration of the entire power system model with a significant improvement in simulation time. Since the proposed methods are based on the state transformation of the power system model, this approach could be used together with other numerical and machine-level programming optimization techniques to further enhance performance of the power system dynamics simulator.