Mass renormalisation for improved staggered quarks

Improved staggered quark actions are designed to suppress flavour changing strong interactions. We discuss the perturbation theory for this type of actions and show the improvements to reduce the quark mass renormalisation compared to naive staggered quarks. The renormalisations are of similar size as for Wilson quarks.Comment: LaTeX, 3 pages, Lattice2001(spectrum

The Low-Lying Dirac Spectrum of Staggered Quarks

We investigate and clarify the role of topology and the issues surrounding the epsilon regime for staggered quarks. We study unimproved and improved staggered quark Dirac operators on quenched lattice QCD gluon backgrounds generated using a Symanzik-improved gluon action. For the improved Dirac operators we find a clear separation of the spectrum into would-be zero modes and others. The number of would-be zero modes depends on the topological charge as predicted by the continuum Index Theorem, and the expectation values of their chirality are large for the most improved actions (approx 0.7). The remaining modes have low chirality and show clear signs of clustering into quartets that become degenerate in the continuum limit. We demonstrate that the lattice spacing and volume dependence of the eigenvalues follow expectations. Furthermore, the non-zero modes follow the random matrix theory predictions for all topological charge sectors. The values of the chiral condensate extracted from fits to the theoretical distributions are consistent with each other, and with the results obtained from the total density of eigenvalues using the Banks-Casher relation. We conclude that staggered quarks respond correctly to QCD topology when both fermion and gauge actions are improved.Comment: 17 pages, a few typos corrected, part of one figure change

Accelerating Aggregation Efficiency: Using Postgres as a Cache with MongoDB

For decades now relational databases, namely SQL, have been the industry standard. However, recently MongoDB and other NoSQL databases have been growing in popularity due to their flexibility and scalability. SQL still has the upper hand in a variety of areas, including data consistency, advanced and established analytics functions, and efficient “JOIN” functions. This project focuses on MongoDB’s shortcomings when it comes to replicating “JOIN” operations using MongoDB’s aggregate functions. “JOIN” operations refer to the action of comparing data from one or more collections of data and joining similar data together in order to analyze and draw statistics from the combined data pool. MongoDB’s performance in regards to these expensive aggregate operations can be accelerated with the help of Postgres, an SQL database management system. By caching, or storing, the results of these MongoDB aggregate operations along with information about the aggregate queries themselves into Postgres, users can greatly improve the performance of MongoDB “JOIN” equivalents. Thus, users can enjoy the benefits of a NoSQL database system without sacrificing the ability to efficiently gather insightful statistics and analytics from the database

Interviews with Philip Barlow and Patrick Q. Mason

Editor\u27s interview with Philip Barlow and Patrick Q. Mason

Predictors of Participant Perceptions of Facilitated Individualized Education Program Meeting Success

Facilitated Individualized Education Program (FIEP) meetings present one option for early, alternative dispute resolution in special education. Although it has been suggested that this process may be useful in resolving disputes and improving relationships, these hypotheses have not been directly addressed. In this study, we used individual participant feedback data collected by a northwestern state over a 2-year period to answer the following research questions: (a) What are the perceived outcomes of FIEP meetings in terms of agreement, reduced future use of procedural safeguards, and improved relationships between school staff and family? and (b) What are the predictors of these positive participant perceptions of the outcomes of FIEP meetings? We found that respondents perceived FIEP meetings to be successful, with more than half of respondents reporting an outcome of full agreement by all team members, 44% reporting reduced future use of procedural safeguards, and 42% reporting an improved relationship between school staff and family following the meeting. Using multilevel models, we found that perceived facilitator quality was a significant predictor of all three positive outcomes, even after controlling for significant meeting characteristics such as region and year. Given these initial findings, we also provide implications for research, practice, and policy

Facilitated Individualized Education Planning: The State of Implementation and Evaluation

Facilitated individualized education planning (FIEP) presents an alternative to formalized dispute resolution procedures, which can have damaging financial and relational consequences for families and schools. Although recommended as an alternative dispute resolution practice, minimal research has examined its implementation and evaluation. In this study, we described where and how FIEP was being implemented and what types of data state educational agencies (SEAs) implementing FIEP were collecting. In two phases, we contacted representatives of each SEA in the United States, asking them to complete a survey on their state’s use of FIEP, and then to share outcome and participant feedback data and data collection forms. From 43 responses in the first phase, we found that almost half of SEAs are using FIEPs (n = 24), and of those not currently using FIEP, 12 were considering implementing the practice in the future. In the second phase of the study, we found that six states that responded to the request for data captured similar content on meeting outcomes and participant feedback. Outcome data provided preliminary, initial evidence for the potential effectiveness of FIEP in achieving positive outcomes in the form of agreement or consensus regarding IEPs. Implications for practice, research, and policy are discussed

Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics

We use perturbative Symanzik improvement to create a new staggered-quark action (HISQ) that has greatly reduced one-loop taste-exchange errors, no tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading order in the quark's velocity v/c. We demonstrate with simulations that the resulting action has taste-exchange interactions that are at least 3--4 times smaller than the widely used ASQTAD action. We show how to estimate errors due to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate with simulations that such errors are no more than 1% when HISQ is used for light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4 errors also makes HISQ the most accurate discretization currently available for simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66, with full-QCD gluon configurations (from MILC). We obtain a result of~111(5) MeV which compares well with experiment. We discuss applications of this formalism to D physics and present our first high-precision results for D_s mesons.Comment: 21 pages, 8 figures, 5 table

High-precision determination of the light-quark masses from realistic lattice QCD

Three-flavor lattice QCD simulations and two-loop perturbation theory are used to make the most precise determination to date of the strange-, up-, and down-quark masses, $m_s$, $m_u$, and $m_d$, respectively. Perturbative matching is required in order to connect the lattice-regularized bare- quark masses to the masses as defined in the \msbar scheme, and this is done here for the first time at next-to-next-to leading (or two-loop) order. The bare-quark masses required as input come from simulations by the MILC collaboration of a highly-efficient formalism (using so-called ``staggered'' quarks), with three flavors of light quarks in the Dirac sea; these simulations were previously analyzed in a joint study by the HPQCD and MILC collaborations, using degenerate $u$ and $d$ quarks, with masses as low as $m_s/8$, and two values of the lattice spacing, with chiral extrapolation/interpolation to the physical masses. With the new perturbation theory presented here, the resulting \msbar\ masses are m^\msbar_s(2 {GeV}) = 87(0)(4)(4)(0) MeV, and \hat m^\msbar(2 {GeV}) = 3.2(0)(2)(2)(0) MeV, where \hat m = \sfrac12 (m_u + m_d) is the average of the $u$ and $d$ masses. The respective uncertainties are from statistics, simulation systematics, perturbation theory, and electromagnetic/isospin effects. The perturbative errors are about a factor of two smaller than in an earlier study using only one-loop perturbation theory. Using a recent determination of the ratio $m_u/m_d = 0.43(0)(1)(0)(8)$ due to the MILC collaboration, these results also imply m^\msbar_u(2 {GeV}) = 1.9(0)(1)(1)(2) MeV and m^\msbar_d(2 {GeV}) = 4.4(0)(2)(2)(2) MeV. A technique for estimating the next order in the perturbative expansion is also presented, which uses input from simulations at more than one lattice spacing

The B Meson Decay Constant from Unquenched Lattice QCD

We present determinations of the B meson decay constant f_B and of the ratio f_{B_s}/f_B using the MILC collaboration unquenched gauge configurations which include three flavors of light sea quarks. The mass of one of the sea quarks is kept around the strange quark mass, and we explore a range in masses for the two lighter sea quarks down to m_s/8. The heavy b quark is simulated using Nonrelativistic QCD, and both the valence and sea light quarks are represented by the highly improved (AsqTad) staggered quark action. The good chiral properties of the latter action allow for a much smoother chiral extrapolation to physical up and down quarks than has been possible in the past. We find f_B = 216(9)(19)(4) (6) MeV and f_{B_s} /f_B = 1.20(3)(1).Comment: 4 pages, 2 figure