Perturbative Improvement for Lattice QCD: An Update

Recent developments in the Symanzik improvement program for lattice QCD are reviewed.Comment: Invited talk at the workshop on "Lattice QCD on Parallel Computers" (Tsukuba, March 1997). One file producing 12 pages; LaTe

Anyons in discrete gauge theories with Chern-Simons terms

We study the effect of a Chern-Simons term in a theory with discrete gauge group H, which in (2+1)-dimensional space time describes (non-abelian) anyons. As in a previous paper, we emphasize the underlying algebraic structure, namely the Hopf algebra D(H). We argue on physical grounds that the addition of a Chern-Simons term in the action leads to a non-trivial 3-cocycle on D(H). Accordingly, the physically inequivalent models are labelled by the elements of the cohomology group H^3(H,U(1)). It depends periodically on the coefficient of the Chern-Simons term which model is realized. This establishes a relation with the discrete topological field theories of Dijkgraaf and Witten. Some representative examples are worked out explicitly.Comment: 18 page

A quark action for very coarse lattices

We investigate a tree-level O(a^3)-accurate action, D234c, on coarse lattices. For the improvement terms we use tadpole-improved coefficients, with the tadpole contribution measured by the mean link in Landau gauge. We measure the hadron spectrum for quark masses near that of the strange quark. We find that D234c shows much better rotational invariance than the Sheikholeslami-Wohlert action, and that mean-link tadpole improvement leads to smaller finite-lattice-spacing errors than plaquette tadpole improvement. We obtain accurate ratios of lattice spacings using a convenient ``Galilean quarkonium'' method. We explore the effects of possible O(alpha_s) changes to the improvement coefficients, and find that the two leading coefficients can be independently tuned: hadron masses are most sensitive to the clover coefficient, while hadron dispersion relations are most sensitive to the third derivative coefficient C_3. Preliminary non-perturbative tuning of these coefficients yields values that are consistent with the expected size of perturbative corrections.Comment: 22 pages, LaTe

Cosmic Electroweak Strings

We examine the Standard Model field configurations near cosmic strings in a particular class of models. This class is defined by the condition that the generator of the flux in the string, $T_s$, commutes with the Standard Model Lie algebra. We find that if the Standard Model Higgs carries a charge $F_h /2$ under $T_s$, cosmic string solutions have Z-flux $\Phi_Z =[n-F_h N/F_{\phi}]4\pi \cos \theta_w /g$, where $n$ is any integer and $4\pi N/qF_{\phi}$ is the flux of the gauge field associated with $T_s$. Only the configuration with the smallest value of $|n-F_h N/F_{\phi}|$ is stable, however. We argue that the instabilities found at higher $\Phi_Z$ are just associated with paths in configuration space reducing $|n-F_h N/F_{\phi}|$ by one unit. This contradicts recent claims that the instabilities in such models represent the spontaneous generation of current along the string. We also show that the stable strings have no Standard Model fermion zero modes: therefore there is no possibility of supercurrents carried by Standard Model particles in this class of models.Comment: Latex, 13 pages, 2 uuencoded figure

Improved SrTiO3 thin films using oxygen relaxation technique

Published versio

Flavor-Symmetry Restoration and Symanzik Improvement for Staggered Quarks

We resolve contradictions in the literature concerning the origins and size of unphysical flavor-changing strong interactions generated by the staggered-quark discretization of QCD. We show that the leading contributions are tree-level in \order(a^2) and that they can be removed by adding three correction terms to the link operator in the standard action. These corrections are part of the systematic Symanzik improvement of the staggered-quark action. We present a new improved action for staggered quarks that is accurate up to errors of \order(a^4,a^2\alpha_s) --- more accurate than most, if not all, other discretizations of light-quark dynamics.Comment: 7 page

The Genetic and Environmental Foundations of Political, Psychological, Social, and Economic Behaviors: A Panel Study of Twins and Families

Here we introduce the Genetic and Environmental Foundations of Political and Economic Behaviors: A Panel Study of Twins and Families (PIs Alford, Hatemi, Hibbing, Martin, and Smith). This study was designed to explore the genetic and environmental influences on social, economic, and political behaviors and attitudes. It involves identifying the psychological mechanisms that operate on these traits, the heritability of complex economic and political traits under varying conditions, and specific genetic correlates of attitudes and behaviors. In addition to describing the study, we conduct novel analyses on the data, estimating the heritability of two traits so far unexplored in the extant literature: Machiavellianism and Baron-Cohen’s Empathizing Quotient

Quantum mechanics of an electron in a homogeneous magnetic field and a singular magnetic flux tube

The eigenvalue problem of the Hamiltonian of an electron confined to a plane and subjected to a perpendicular time-independent magnetic field which is the sum of a homogeneous field and an additional field contributed by a singular flux tube, i.e. of zero width, is investigated. Since both a direct approach based on distribution-valued operators and a limit process starting from a non-singular flux tube, i.e. of finite size, fail, an alternative method is applied leading to consistent results. An essential feature is quantum mechanical supersymmetry at g=2 which imposes, by proper representation, the correct choice of "boundary conditions". The corresponding representation of the Hilbert space in coordinate space differs from the usual space of square-integrable 2-spinors, entailing other unusual properties. The analysis is extended to $g\ne 2$ so that supersymmetry is explicitly broken. Finally, the singular Aharonov-Bohm system with the same amount of singular flux is analysed by making use of the fact that the Hilbert space must be the same.Comment: 23 pages, LaTeX, minor change