Non-abelian dynamics in first-order cosmological phase transitions

Bubble collisions in cosmological phase transitions are explored, taking the non-abelian character of the gauge fields into account. Both the QCD and electroweak phase transitions are considered. Numerical solutions of the field equations in several limits are presented.Comment: 8 pages, 2 figures. Contribution to the CosPA 2003 Cosmology and Particle Astrophysics Symposium. Typos correcte

Phason elasticity of a three-dimensional quasicrystal: transfer-matrix method

We introduce a new transfer matrix method for calculating the thermodynamic properties of random-tiling models of quasicrystals in any number of dimensions, and describe how it may be used to calculate the phason elastic properties of these models, which are related to experimental measurables such as phason Debye-Waller factors, and diffuse scattering wings near Bragg peaks. We apply our method to the canonical-cell model of the icosahedral phase, making use of results from a previously-presented calculation in which the possible structures for this model under specific periodic boundary conditions were cataloged using a computational technique. We give results for the configurational entropy density and the two fundamental elastic constants for a range of system sizes. The method is general enough allow a similar calculation to be performed for any other random tiling model.Comment: 38 pages, 3 PostScript figures, self-expanding uuencoded compressed tar file, LaTeX using RevTeX macros and epsfig.st

The "supporting kids, avoiding problems" (SKIP) study: Relationships between school exclusion, psychopathology, development and attainment - Case control study

PublishedJournal ArticlePurpose - The purpose of this paper is to explore the association between children who are at risk of being or who have been excluded from school between the ages of 4 and 12 years and the role of psychopathology, development and attainment. Design/methodology/approach - A case-control approach was conducted. Cases were children who had been excluded from school compared to those who had no reported exclusions and normative data where possible. A range of measures were used to collect information from the parent, child and teacher on areas covering the child's mental health and well-being. Findings - The findings showed the number of difficulties faced by children who are at risk of being or who have been excluded from school compared to gender- nd age-matched controls and normative data increased. Behavioural difficulties were apparent in the majority of the cases and an alarming number of children reported self-harm. Interestingly nearly all the cases had recognised needs, but not all of them were accessing appropriate services. Practical implications - There have been a number of changes regarding the identification and support of children's mental health and well-being. This study highlights gaps in resources and provision, particularly around behavioural difficulties for children who are presenting as not coping in school. Originality/value - The findings from the SKIP study indicate the complexities and compounded difficulties faced by children who are experiencing exclusion from school. By implementing a systematic group of assessments the study was able to identify these complexities of need across a vulnerable group of children.The authors would like to thank all the children, their families and the schools for taking part in the study. The authors are grateful for all the support that has been provided by a number of services and individuals across the county. The authors are grateful to the Peninsula CLAHRC for funding Claire Parker’s doctoral studentship. This paper presents independent research funded by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) for the South West Peninsula. The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health in England

An SU(4) Model of High-Temperature Superconductivity and Antiferromagnetism

We present an SU(4) model of high-temperature superconductivity having many similarities to dynamical symmetries known to play an important role in microscopic nuclear structure physics and in elementary particle physics. Analytical solutions in three dynamical symmetry limits of this model are found: an SO(4) limit associated with antiferromagnetic order; an SU(2) X SO(3) limit that may be interpreted as a d-wave pairing condensate; and an SO(5) limit that may be interpreted as a doorway state between the antiferromagnetic order and the superconducting order. The model suggests a phase diagram in qualitative agreement with that observed in the cuprate superconductors. The relationship between the present model and the SO(5) unification of superconductivity and antiferromagnetic order proposed by Zhang is discussed.Comment: A long paper extended from the early version cond-mat/9903150; accepted by Phys. Rev.

Aspirin reduces cardiovascular events in patients with pneumonia: a prior event rate ratio analysis in a large primary care database

This is the author accepted manuscript. The final version is available from the European Respiratory Society via the DOI in this recordData sharing and dissemination: Unfortunately, CPRD does not allow direct data-sharing due to patient confidentiality issues. The lead author would welcome informal and formal contact if required. It is not feasible to disseminate results back to individual patients within the CPRD.BACKGROUND: Ischaemic stroke and myocardial infarction (MI) are common after pneumonia and are associated with long-term mortality. Aspirin may attenuate this risk and should be explored as a therapeutic option. METHODS: We extracted all patients with pneumonia, aged over 50, from the Clinical Practice Research Datalink (CPRD), a large UK primary care database, from inception until January 2019. We then performed a prior event rate ratio analysis (PERR) with propensity score matching, an approach that allows for control of measured and unmeasured confounding, with aspirin usage as the exposure, and ischaemic events as the outcome. The primary outcome was the combined outcome of ischaemic stroke and myocardial infarction. Secondary outcomes were ischaemic stroke and myocardial infarction individually. Relevant confounders were included in the analysis (smoking, comorbidities, age, gender). FINDINGS: 48 743 patients were eligible for matching. 8099 of these were aspirin users who were matched to 8099 non-users. Aspirin users had a reduced risk of the primary outcome (adjusted hazard ratio, HR 0.64; 95% confidence interval 0.52-0.79) in the PERR analysis. For both secondary outcomes, aspirin use was also associated with a reduced risk HR 0.46 (0.30-0.72) and HR 0.70 (0.55-0.91) for myocardial infarction and stroke respectively). INTERPRETATION: This study provides supporting evidence that aspirin use is associated with reduced ischaemic events after pneumonia in a primary care setting. This drug may have a future clinical role in preventing this important complication.National Institute for Health Research (NIHR

Criticality, the area law, and the computational power of PEPS

The projected entangled pair state (PEPS) representation of quantum states on two-dimensional lattices induces an entanglement based hierarchy in state space. We show that the lowest levels of this hierarchy exhibit an enormously rich structure including states with critical and topological properties as well as resonating valence bond states. We prove, in particular, that coherent versions of thermal states of any local 2D classical spin model correspond to such PEPS, which are in turn ground states of local 2D quantum Hamiltonians. This correspondence maps thermal onto quantum fluctuations, and it allows us to analytically construct critical quantum models exhibiting a strict area law scaling of the entanglement entropy in the face of power law decaying correlations. Moreover, it enables us to show that there exist PEPS within the same class as the cluster state, which can serve as computational resources for the solution of NP-hard problems

Parity-Violating Interaction Effects in the np System

We investigate parity-violating observables in the np system, including the longitudinal asymmetry and neutron-spin rotation in np elastic scattering, the photon asymmetry in np radiative capture, and the asymmetries in deuteron photo-disintegration d(gamma,n)p in the threshold region and electro-disintegration d(e,e`)np in quasi-elastic kinematics. To have an estimate of the model dependence for the various predictions, a number of different, latest-generation strong-interaction potentials--Argonne v18, Bonn 2000, and Nijmegen I--are used in combination with a weak-interaction potential consisting of pi-, rho-, and omega-meson exchanges--the model known as DDH. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials is solved in both configuration and momentum space. The issue of electromagnetic current conservation is examined carefully. We find large cancellations between the asymmetries induced by the parity-violating interactions and those arising from the associated pion-exchange currents. In the np capture, the model dependence is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant E1 matrix elements. In quasi-elastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by gamma-Z interference on individual nucleons.Comment: 65 pages, 26 figures, submitted to PR

J1−J2J_1-J_2 quantum Heisenberg antiferromagnet on the triangular lattice: a group symmetry analysis of order by disorder

On the triangular lattice, for $J_2/J_1$ between $1/8$ and $1$, the classical Heisenberg model with first and second neighbor interactions presents four-sublattice ordered ground-states. Spin-wave calculations of Chubukov and Jolicoeur\cite{cj92} and Korshunov\cite{k93} suggest that quantum fluctuations select amongst these states a colinear two-sublattice order. From theoretical requirements, we develop the full symmetry analysis of the low lying levels of the spin-1/2 Hamiltonian in the hypotheses of either a four or a two-sublattice order. We show on the exact spectra of periodic samples ($N=12,16$ and $28$) how quantum fluctuations select the colinear order from the four-sublattice order.Comment: 15 pages, 4 figures (available upon request), Revte

Scaling laws and simulation results for the self--organized critical forest--fire model

We discuss the properties of a self--organized critical forest--fire model which has been introduced recently. We derive scaling laws and define critical exponents. The values of these critical exponents are determined by computer simulations in 1 to 8 dimensions. The simulations suggest a critical dimension $d_c=6$ above which the critical exponents assume their mean--field values. Changing the lattice symmetry and allowing trees to be immune against fire, we show that the critical exponents are universal.Comment: 12 pages, postscript uuencoded, figures included, to appear in Phys. Rev.

Testing the Meson Cloud Model in Inclusive Meson Production

We have applied the Meson Cloud Model to calculate inclusive momentum spectra of pions and kaons produced in high energy proton-proton and proton-nucleus collisions. For the first time these data are used to constrain the cloud cut-off parameters. We show that it is possible to obtain a reasonable description of data, especially the large $x_F$ ($x_F \geq 0.2$) part of the spectrum and at the same time describe (partially) the E866 data on $\bar d - \bar u$ and $\bar d / \bar u$. We also discuss the relative strength of the $\pi N$ and $\pi \Delta$ vertices. We find out that the corresponding cut-off parameters should be both soft and should not differ by more than 200 MeV from each other. An additional source (other than the meson cloud) of sea antiquark asymmetry, seems to be necessary to completely explain the data. A first extension of the MCM to proton nucleus collisions is discussed.Comment: 14 pages, Latex, 6 ps figures. Submitted to Phys. Rev.