Towards a precision computation of f_Bs in quenched QCD

We present a computation of the decay constant f_Bs in quenched QCD. Our strategy is to combine new precise data from the static approximation with an interpolation of the decay constant around the charm quark mass region. This computation is the first step in demonstrating the feasability of a strategy for f_B in full QCD. The continuum limits in the static theory and at finite mass are taken separately and will be further improved.Comment: Lattice2003(heavy), 3 pages, 2 figure

Investigation of the fine structure of antihydrogen.

At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2-5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2-2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2-2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system

String breaking and lines of constant physics in the SU(2) Higgs model

We present results for the ground state and first excited state static potentials in the confinement "phase" of the SU(2) Higgs model. String breaking and the crossing of the energy levels are clearly visible. We address the question of the cut-off effects in our results and observe a remarkable scaling of the static potentials.Comment: LATTICE99(Higgs), 3 pages, 4 figure

A strategy for implementing non-perturbative renormalisation of heavy-light four-quark operators in the static approximation

We discuss the renormalisation properties of the complete set of $\Delta B = 2$ four-quark operators with the heavy quark treated in the static approximation. We elucidate the role of heavy quark symmetry and other symmetry transformations in constraining their mixing under renormalisation. By employing the Schroedinger functional, a set of non-perturbative renormalisation conditions can be defined in terms of suitable correlation functions. As a first step in a fully non-perturbative determination of the scale-dependent renormalisation factors, we evaluate these conditions in lattice perturbation theory at one loop. Thereby we verify the expected mixing patterns and determine the anomalous dimensions of the operators at NLO in the Schroedinger functional scheme. Finally, by employing twisted-mass QCD it is shown how finite subtractions arising from explicit chiral symmetry breaking can be avoided completely.Comment: 41 pages, 6 figure

A perturbative study of two four-quark operators in finite volume renormalization schemes

Starting from the QCD Schroedinger functional (SF), we define a family of renormalization schemes for two four-quark operators, which are, in the chiral limit, protected against mixing with other operators. With the appropriate flavour assignments these operators can be interpreted as part of either the $\Delta F=1$ or $\Delta F=2$ effective weak Hamiltonians. In view of lattice QCD with Wilson-type quarks, we focus on the parity odd components of the operators, since these are multiplicatively renormalized both on the lattice and in continuum schemes. We consider 9 different SF schemes and relate them to commonly used continuum schemes at one-loop order of perturbation theory. In this way the two-loop anomalous dimensions in the SF schemes can be inferred. As a by-product of our calculation we also obtain the one-loop cutoff effects in the step-scaling functions of the respective renormalization constants, for both O(a) improved and unimproved Wilson quarks. Our results will be needed in a separate study of the non-perturbative scale evolution of these operators.Comment: 22 pages, 4 figure

Controlling turbulent drag across electrolytes using electric fields

Reversible in operando control of friction is an unsolved challenge crucial to industrial tribology. Recent studies show that at low sliding velocities, this control can be achieved by applying an electric field across electrolyte lubricants. However, the phenomenology at high sliding velocities is yet unknown. In this paper, we investigate the hydrodynamic friction across electrolytes under shear beyond the transition to turbulence. We develop a novel, highly parallelised, numerical method for solving the coupled Navier-Stokes Poisson-Nernest-Planck equation. Our results show that turbulent drag cannot be controlled across dilute electrolyte using static electric fields alone. The limitations of the Poisson-Nernst-Planck formalism hints at ways in which turbulent drag could be controlled using electric fields.Comment: Accepted by the Faraday Discussions on Chemical Physics of Electroactive Material

How Public Is the Internet? A Conversation on the Nature of Human Interactions On-line and the Implications for Research Methods

In the past decade, ???virtual??? research???empirical investigations conducted via the Internet???has increased dramatically across a variety of disparate disciplines. Areas such as cybersecurity and encryption, digital government and citizenship, consumer health informatics, and user behavior in online spaces have emerged to become signature iSchool research areas, often shared with particular disciplinary heritages (e.g., computer science, political science and communication, public health, and sociology???respectively, but not exclusively). In addition, the field of Information Science is dominated by research developing or using emerging technologies. These new technologies often occupy a gray area in which ethical issues either have not been sufficiently well-defined or push against existing definitions. Questions surrounding the ???public??? nature of the internet and Web 2.0-era information technologies have also emerged and have become increasingly urgent given the tightening of federal, state and University regulations as they relate to the protection of human subjects. At the convergence of multiple disciplinary and methodological perspectives, Information Science researchers are well-positioned to become more active participants in both scholarly and institutional conversations regarding the appropriate risks and benefits that participants in online research studies might be subject to. Critiques of IRB inconsistencies exist, what we need is a thoughtful and thorough community response to the innately complex nature of virtual research and a map which can guide us towards the future and the study of twenty-first century systems, selves and societies. Our goal for this wildcard event, is to generate a lively and rigorous debate which accomplishes the following three goals: 1) extends the dialogue within the Information Science field concerning the beneficence and respect for participants in online research; 2) enumerates a set of best practices for iSchool researchers in relation to conducting approved research on-line and; 3) moves us towards the process of drafting an iSchool set of ethical guidelines related to virtual research

Effective heavy-light meson energies in small-volume quenched QCD

We study effective energies of heavy-light meson correlation functions in lattice QCD and a small volume of (0.2 fm)^4 to non-perturbatively calculate their dependence on the heavy quark mass in the continuum limit. Our quenched results obtained here constitute an essential intermediate step of a first fully non-perturbative computation of the b-quark's mass in the static approximation that has recently been presented as an application of a new proposal to non-perturbatively renormalize the Heavy Quark Effective Theory. The renormalization constant and the improvement coefficients relating the renormalized current and subtracted quark mass are determined in the relevant parameter region at weak couplings, which allows to perform the numerical simulations at several, precisely fixed values of the renormalization group invariant heavy quark mass in a range from 3 GeV to 15 GeV.Comment: 24 pages including figures and tables, latex2e; version published in JHEP, small additions, results unchange