Quantum Vibrational Impurity Embedded in a One-dimensional Chain

We perform a fully quantum mechanical numerical calculation for the problem of a single electron (or excitation) propagating in a N-site one-dimensional chain in the presence of a single Holstein impurity. We compute the long-time averaged probability for finding the electron on the impurity site as a function of the nonlinearity parameter, defined in terms of the electron-phonon coupling strength and the oscillator frequency. The results, in the intermediate nonlinearity parameter range, differ substantially from the ones obtained through the use of the discrete nonlinear Schroedinger equation, even in the high-frequency regime.Comment: 8 pages, 4 figure

Quartic Gauge Couplings and the Radiation Zero in pp to l nu gamma gamma events at the LHC

We report a study of the process pp to l nu gamma gamma at CERN's Large Hadron Collider, using a leading order partonic-level event generator interfaced to the Pythia program for showering and hadronisation and a with a generic detector simulation. The process is sensitive to possible anomalous quartic gauge boson couplings of the form W W gamma gamma. It is shown how unitarity-safe limits may be placed on these anomalous couplings by applying a binned maximum likelihood fit to the distribution of the two-photon invariant mass, M(gamma gamma), below a cutoff of 1TeV. Assuming 30fb-1 of integrated luminosity, the expected limits are two orders of magnitude tighter than those available from LEP. It is also demonstrated how the Standard Model radiation zero feature of the qq to W gamma gamma process may be observed in the difference between the two-photon and charged lepton pseudo-rapidities.Comment: 9 pages, 7 figure

Generalized resummation of QCD final-state observables

The resummation of logarithmically-enhanced terms to all perturbative orders is a prerequisite for many studies of QCD final-states. Until now such resummations have always been performed by hand, for a single observable at a time. In this letter we present a general `master' resummation formula (and applicability conditions), suitable for a large class of observables. This makes it possible for next-to-leading logarithmic resummations to be carried out automatically given only a computer routine for the observable. To illustrate the method we present the first next-to-leading logarithmic resummed prediction for an event shape in hadronic dijet production.Comment: 9 pages, 1 figure; v2 includes substantial amplifications and clarification

Giant Alcohol: A Worthy Opponent for the Children of the Band of Hope

From its foundation in 1847, the temperance organisation the Band of Hope addressed its young members as consumers, victims, and agents. In the first two roles they encountered the effects of drink of necessity, but in the third role they were encouraged to seek it out, attempting to influence individuals and wider society against 'Giant Alcohol'. With an estimated membership of half the school-age population by the early twentieth century, well over three million, the Band of Hope also acted more directly to influence policy, and encouraged young people to consider issues of policy and politics. With its wide range of activities and material to educate, entertain and empower millions of children, and its radical view of the place of the child, the Band of Hope not only mobilised its child members to lobby for legal change, including prohibition, but took an active part in pointing out the cost of alcohol to society, particularly during the 14-18 war. The organisation began to decline post 1918, and this paper focuses on the address made to children by the Band of Hope in the late nineteenth and early twentieth centuries, at a time when its innovative view of children as able to understand and influence policy decisions reflected developments in the construction of childhood. This article draws on the archive of the British National Temperance League, over 50,000 items located in the Livesey Collection, University of Central Lancashire

Distinguishing the dimensions of the original dysfunctional attitude scale in an archival clinical sample

The Dysfunctional Attitude Scale measures depression related enduring beliefs and is one of the central measures of cognitive behavioral (CBT) research and theory. It has been the central marker of etiological claims of CBT, and so any change to the understanding of the composition of the DAS would have potentially far-reaching implications for a large body of literature. We sought to capitalize on advances in psychometric techniques since the original 100-item DAS was last analyzed in a sufficiently large clinical sample to provide a definitive measurement model of this important instrument. Beyond the two dimensions usually found on the shorter forms of the scale, we identified the following subscales: imperatives, cognitive flexibility, and negative expectancy. This richer and more precise DAS structure renews its potential to meet the challenge of predicting who is prone to develop depression or experience a recurrence

TASI Lectures on the Cosmological Constant

The energy density of the vacuum, Lambda, is at least 60 orders of magnitude smaller than several known contributions to it. Approaches to this problem are tightly constrained by data ranging from elementary observations to precision experiments. Absent overwhelming evidence to the contrary, dark energy can only be interpreted as vacuum energy, so the venerable assumption that Lambda=0 conflicts with observation. The possibility remains that Lambda is fundamentally variable, though constant over large spacetime regions. This can explain the observed value, but only in a theory satisfying a number of restrictive kinematic and dynamical conditions. String theory offers a concrete realization through its landscape of metastable vacua.Comment: 39 pages, 3 figure

Scale Setting in QCD and the Momentum Flow in Feynman Diagrams

We present a formalism to evaluate QCD diagrams with a single virtual gluon using a running coupling constant at the vertices. This method, which corresponds to an all-order resummation of certain terms in a perturbative series, provides a description of the momentum flow through the gluon propagator. It can be viewed as a generalization of the scale-setting prescription of Brodsky, Lepage and Mackenzie to all orders in perturbation theory. In particular, the approach can be used to investigate why in some cases the ``typical'' momenta in a loop diagram are different from the ``natural'' scale of the process. It offers an intuitive understanding of the appearance of infrared renormalons in perturbation theory and their connection to the rate of convergence of a perturbative series. Moreover, it allows one to separate short- and long-distance contributions by introducing a hard factorization scale. Several applications to one- and two-scale problems are discussed in detail.Comment: eqs.(51) and (83) corrected, minor typographic changes mad

Magnetic reversal processes and critical thickness in FePt/{\alpha}-Fe/FePt trilayers

Magnetic reversal processes of a FePt/{\alpha}-Fe/FePt trilayer system with in-plane easy axes have been investigated within a micromagnetic approach. It is found that the magnetic reversal process consists of three steps: nucleation of a prototype of domain wall in the soft phase, the evolution as well as the motion of the domain wall from the soft to the hard phase and finally, the magnetic reversal of the hard phase. For small soft layer thickness Ls, the three steps are reduced to one single step, where the magnetizations in the two phases reverse simultaneously and the hysteresis loops are square with nucleation as the coercivity mechanism. As Ls increases, both nucleation and pinning fields decrease. In the meantime, the single-step reversal expands to a standard three-step one and the coercivity mechanism changes from nucleation to pinning. The critical thickness where the coercivity mechanism alters, could be derived analytically, which is found to be inversely proportional to the square root of the crystalline anisotropy of the hard phase. Further increase of Ls leads to the change of the coercivity mechanism from pinning to nucleation.Comment: 21 pages, 5 figures, pdf file, figures include

Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions

We calculate the cross sections for the production of one and more electron-positron pairs due to the strong electromagnetic fields in relativistic heavy ion collisions. Using the generating functional of fermions in an external field we derive the N-pair amplitude. Neglecting the antisymmetrisation in the final state we find that the total probability to produce N pairs is a Poisson distribution. We calculate total cross sections for the production of one pair in lowest order and also include higher-order corrections from the Poisson distribution up to third order. Furthermore we calculate cross sections for the production of up to five pairs including corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may also be obtained from http://www.phys.washington.edu/~hencken

Nucleon Axial Form Factor from Lattice QCD

Results for the isovector axial form factors of the proton from a lattice QCD calculation are presented for both point-split and local currents. They are obtained on a quenched $16^{3} \times 24$ lattice at $\beta= 6.0$ with Wilson fermions for a range of quark masses from strange to charm. We determine the finite lattice renormalization for both the local and point-split currents of heavy quarks. Results extrapolated to the chiral limit show that the $q^2$ dependence of the axial form factor agrees reasonably well with experiment. The axial coupling constant $g_A$ calculated for the local and the point-split currents is about 6\% and 12\% smaller than the experimental value respectively.Comment: 8 pages, 5 figures (included in part 2), UK/93-0