Wavepacket Dynamics in Yang-Mills Theory

We discuss the results of numerical simulations of colliding wavepackets in $SU(2)$ Yang--Mills theory. We investigate their behavior as a function of amplitude and momentum distribution. We find regions in our parameter space in which initial wave packets scatter into final configurations with dramatically different momentum distributions. These results constitute new classical trajectories with multiparticle boundary conditions. We explain their relevance for the calculation of scattering amplitudes in the semiclassical approximation. Finally, we give directions for future work.Comment: 11 pgs. text, 11 optional figs using PiCTeX and epsf, new version contains improved discussion of scaling properties of results and one additional figure

Improving estimation of the prognosis of childhood psychopathology; combination of DSM-III-R/DISC diagnoses and CBCL scores [IF: 2.7]

Objective: To compare the predictive validity of the clinical-diagnostic and the empirical-quantitative approach to assessment of childhood psychopathology, and to investigate the usefulness of combining both approaches. Method: A referred sample (N=96), aged 6 to 12 years at initial assessment, was followed up across - on average - a period of 3.2 years. It was assessed to what extent DISC/DSM-III-R diagnoses - representing the clinical-diagnostic approach, and CBCL scores - representing the empirical-quantitative approach, predicted the following signs of poor outcome: outpatient/inpatient treatment, or parents' wish for professional help for the child at follow-up, disciplinary problems in school, and police/judicial contacts. Results: Both diagnostic systems added significantly to the prediction of poor outcome, and neither of the two systems was superior. Use of both systems simultaneously provided the most accurate estimation of the prognosis, reflected by the occurrence of future poor outcome. Even diagnostic concepts that are generally regarded as relatively similar, such as ADHD (DSM) and attention problems (CBCL), or conduct disorder (DSM) and delinquent behavior (CBCL), appeared to differ in their ability to predict poor outcome. Conclusions: The present study supports the use of the empirical-quantitative approach and the clinical-diagnostic approach simultaneously, both in research and in clinical settings, to obtain a comprehensive view of the prognosis of psychopathology in children. © Association for Child Psychology and Psychiatry, 2004

Bounds on the dipole moments of the tau-neutrino via the process e+e−→ννˉγe^{+}e^{-}\rightarrow \nu \bar \nu \gamma in a 331 model

We obtain limits on the anomalous magnetic and electric dipole moments of the $\nu_{\tau}$ through the reaction $e^{+}e^{-}\rightarrow \nu \bar \nu \gamma$ and in the framework of a 331 model. We consider initial-state radiation, and neglect $W$ and photon exchange diagrams. The results are based on the data reported by the L3 Collaboration at LEP, and compare favorably with the limits obtained in other models, complementing previous studies on the dipole moments.Comment: 13 pages, 4 figures, to be published in The European Physical J C. arXiv admin note: substantial text overlap with arXiv:hep-ph/060527

The decay Z -> neutrino antineutrino photon in the Standard Model

A complete study of the one-loop induced decay Z -> neutrino antineutrino photon is presented within the framework of the Standard Model. The advantages of using a nonlinear gauge are stressed. We have found that the main contributions come from the electric dipole and the magnetic dipole transitions of the Z gauge boson and the neutrino, respectively. We obtain a branching ratio B=7.16E-10, which is about four orders of magnitude smaller than the bound recentely obtained by the L3 collaboration and thus it leaves open a window to search for new physics effects in single-photon decays of the Z boson.Comment: REVTEX,15 pp, 5 eps figures, Approved for publication in Physical Review

Social Cohesion, Structural Holes, and a Tale of Two Measures

EMBARGOED - author can archive pre-print or post-print on any open access repository after 12 months from publication. Publication date is May 2013 so embargoed until May 2014.This is an author’s accepted manuscript (deposited at arXiv arXiv:1211.0719v2 [physics.soc-ph] ), which was subsequently published in Journal of Statistical Physics May 2013, Volume 151, Issue 3-4, pp 745-764. The final publication is available at link.springer.com http://link.springer.com/article/10.1007/s10955-013-0722-

Formation and Evolution of Supermassive Black Holes

The correlation between the mass of supermassive black holes in galaxy nuclei and the mass of the galaxy spheroids or bulges (or more precisely their central velocity dispersion), suggests a common formation scenario for galaxies and their central black holes. The growth of bulges and black holes can commonly proceed through external gas accretion or hierarchical mergers, and are both related to starbursts. Internal dynamical processes control and regulate the rate of mass accretion. Self-regulation and feedback are the key of the correlation. It is possible that the growth of one component, either BH or bulge, takes over, breaking the correlation, as in Narrow Line Seyfert 1 objects. The formation of supermassive black holes can begin early in the universe, from the collapse of Population III, and then through gas accretion. The active black holes can then play a significant role in the re-ionization of the universe. The nuclear activity is now frequently invoked as a feedback to star formation in galaxies, and even more spectacularly in cooling flows. The growth of SMBH is certainly there self-regulated. SMBHs perturb their local environment, and the mergers of binary SMBHs help to heat and destroy central stellar cusps. The interpretation of the X-ray background yields important constraints on the history of AGN activity and obscuration, and the census of AGN at low and at high redshifts reveals the downsizing effect, already observed for star formation. History appears quite different for bright QSO and low-luminosity AGN: the first grow rapidly at high z, and their number density decreases then sharply, while the density of low-luminosity objects peaks more recently, and then decreases smoothly.Comment: 31 pages, 13 figures, review paper for Astrophysics Update

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Spectral flow of chiral fermions in nondissipative Yang-Mills gauge field backgrounds

Real-time anomalous fermion number violation is investigated for massless chiral fermions in spherically symmetric SU(2) Yang-Mills gauge field backgrounds which can be weakly dissipative or even nondissipative. Restricting consideration to spherically symmetric fermion fields, the zero-eigenvalue equation of the time-dependent effective Dirac Hamiltonian is studied in detail. For generic spherically symmetric SU(2) gauge fields in Minkowski spacetime, a relation is presented between the spectral flow and two characteristics of the background gauge field. These characteristics are the well-known ``winding factor,'' which is defined to be the change of the Chern-Simons number of the associated vacuum sector of the background gauge field, and a new ``twist factor,'' which can be obtained from the zero-eigenvalue equation of the effective Dirac Hamiltonian but is entirely determined by the background gauge field. For a particular class of (weakly dissipative) Luscher-Schechter gauge field solutions, the level crossings are calculated directly and nontrivial contributions to the spectral flow from both the winding factor and the twist factor are observed. The general result for the spectral flow may be relevant to electroweak baryon number violation in the early universe.Comment: REVTeX, 43 pages, v4: final versio

Small Change: Economics and the British coin-tree

This is the accepted manuscript for the following article: Ceri Houlbrook, “Small Change: Economics and the British coin-tree”, Post Medieval Archaeology, Vol. 49(1), June 2015. The final published version can be found at: http://www.tandfonline.com/doi/full/10.1179/0079423615Z.00000000074 © Society for Post-Medieval Archaeology 2015Throughout the c.2000 year period coins have been circulated in Britain, they have also been ritually employed, most notably as votive deposits. Focusing specifically on the understudied custom of the British coin-tree, whereby coins are ritually embedded into the barks of trees, this paper considers the coin’s role and applicability as a deposit. It aims to demonstrate that our understanding of the coin’s past, present, and future ritual employment is not only aided by a consideration of economics and the coin’s secular function; it would be utterly incomplete without it.Peer reviewedFinal Accepted Versio