Mass dependence of the hairpin vertex in quenched QCD

The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a key role in quenched chiral perturbation theory. Direct calculations using lattice simulations find that it has a significant dependence on quark mass. I show that this mass dependence can be used to determine the quenched Gasser-Leutwyler constant L5. This complements the calculation of L5 using the mass dependence of the axial decay constant of the pion. In an appendix, I discuss power counting for quenched chiral perturbation theory and describe the particular scheme used in this paper.Comment: 12 pages, 4 figures. Version to appear in Phys. Rev. D. Central result unchanged, but explanation of calculation improved and minor errors corrected. New appendix discusses power counting schemes in quenched chiral perturbation theor

Heterotic compactifications with principal bundles for general groups and general levels

We examine to what extent heterotic string worldsheets can describe arbitrary E8xE8 gauge fields. The traditional construction of heterotic strings builds each E8 via a Spin(16)/Z2 subgroup, typically realized as a current algebra by left-moving fermions, and as a result, only E8 gauge fields reducible to Spin(16)/Z2 gauge fields are directly realizable in standard constructions. However, there exist perturbatively consistent E8 gauge fields which can not be reduced to Spin(16)/Z2, and so cannot be described within standard heterotic worldsheet constructions. A natural question to then ask is whether there exists any (0,2) SCFT that can describe such E8 gauge fields. To answer this question, we first show how each ten-dimensional E8 partition function can be built up using other subgroups than Spin(16)/Z2, then construct ``fibered WZW models'' which allow us to explicitly couple current algebras for general groups and general levels to heterotic strings. This technology gives us a very general approach to handling heterotic compactifications with arbitrary principal bundles. It also gives us a physical realization of some elliptic genera constructed recently by Ando and Liu.Comment: 48 pages, LaTeX; v2: references added; v3: typos fixe

Nucleon-Nucleon Interactions on the Lattice

We consider the nucleon-nucleon potential in quenched and partially-quenched QCD. The leading one-meson exchange contribution to the potential is found to fall off exponentially at long-distances, in contrast with the Yukawa-type behaviour found in QCD. This unphysical component of the two-nucleon potential has important implications for the extraction of nuclear properties from lattice simulations.Comment: 6 pages LaTeX, 2 eps fig

Time management issues in COTS distributed simulation: A case study

Commercial off-the-shelf (COTS) simulation packages are widely used in industry. Several international groups are currently investigating techniques to integrate distributed simulation facilities in these packages. Through the use of a case study developed with the Ford Motor Company, this paper investigates time management issues in COTS simulation packages. Time management is classified on the basis of the ordering of events that are externally produced to a federate and the ordering of these with events that occur within a COTS simulation package federate. Several approaches to the latter are discussed and one approach is presented as the most effective. Finally the paper presents a bounded buffer problem and proposes the classification of information sharing with respect to the certification of solution

Enhanced chiral logarithms in partially quenched QCD

I discuss the properties of pions in ``partially quenched'' theories, i.e. those in which the valence and sea quark masses, $m_V$ and $m_S$, are different. I point out that for lattice fermions which retain some chiral symmetry on the lattice, e.g. staggered fermions, the leading order prediction of the chiral expansion is that the mass of the pion depends only on $m_V$, and is independent of $m_S$. This surprising result is shown to receive corrections from loop effects which are of relative size $m_S \ln m_V$, and which thus diverge when the valence quark mass vanishes. Using partially quenched chiral perturbation theory, I calculate the full one-loop correction to the mass and decay constant of pions composed of two non-degenerate quarks, and suggest various combinations for which the prediction is independent of the unknown coefficients of the analytic terms in the chiral Lagrangian. These results can also be tested with Wilson fermions if one uses a non-perturbative definition of the quark mass.Comment: 14 pages, 3 figures, uses psfig. Typos in eqs (18)-(20) corrected (alpha_4 is replaced by alpha_4/2

Matrix Elements of Twist-2 Operators in Quenched Chiral Perturbation Theory

We compute the leading non-analytic quark mass dependence of the matrix elements of isovector twist-2 operators between octet baryon states in quenched QCD using quenched chiral perturbation theory. There are contributions of the form m_q log m_q, in analogy with QCD, but there are also contributions of the form log m_q from hairpin interactions. The nucleon does not receive such hairpin contributions.Comment: 16 pages, 5 eps figs., late

GLSM realizations of maps and intersections of Grassmannians and Pfaffians

In this paper we give gauged linear sigma model (GLSM) realizations of a number of geometries not previously presented in GLSMs. We begin by describing GLSM realizations of maps including Veronese and Segre embeddings, which can be applied to give GLSMs explicitly describing constructions such as the intersection of one hypersurface with the image under some map of another. We also discuss GLSMs for intersections of Grassmannians and Pfaffians with one another, and with their images under various maps, which sometimes form exotic constructions of Calabi-Yaus, as well as GLSMs for other exotic Calabi-Yau constructions of Kanazawa. Much of this paper focuses on a specific set of examples of GLSMs for intersections of Grassmannians G(2,N) with themselves after a linear rotation, including the Calabi-Yau case N=5. One phase of the GLSM realizes an intersection of two Grassmannians, the other phase realizes an intersection of two Pfaffians. The GLSM has two nonabelian factors in its gauge group, and we consider dualities in those factors. In both the original GLSM and a double-dual, one geometric phase is realized perturbatively (as the critical locus of a superpotential), and the other via quantum effects. Dualizing on a single gauge group factor yields a model in which each geometry is realized through a simultaneous combination of perturbative and quantum effects.Comment: LaTeX, 50 pages; v2: typos fixed and a few comments on other dualities adde