Higher order curvature generalisations of Bartnick-McKinnon and coloured black hole solutions in d=5d=5

We construct globally regular as well as non-abelian black hole solutions of a higher order curvature Einstein-Yang-Mills (EYM) model in $d=5$ dimensions. This model consists of the superposition of the first two members of the gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with the superposition of the first two members of the $SO(d)$ Yang--Mills hierarchy.Comment: 13 Revtex pages, 5 PS figures; discussions extended, reference adde

Constraining the Cosmic Star Formation Rate with the MeV Background

The Cosmic Gamma-ray Background (CGB) in the MeV regime has been measured with COMPTEL and SMM. The origin of the CGB in this energy regime is believed to be dominated by gamma-rays from Type Ia supernovae. We calculate the CGB spectrum within the framework of FRW cosmology as a function of the cosmic star formation rate, SFR(z). Several estimates of the SFR(z) have been reported since the pioneering work of Madau et al. Here we discuss observational constraints on SFR(z) derived from models of the CGB. In particular, we consider the SFR obtained from Gamma-Ray Burst observations, which increases dramatically with redshift beyond z ~ 1 in contrast to most estimates which saturate or show a mild increase with redshift. Gamma-ray bursts may be the most powerful tracers of star formation in the early universe and thus provide signposts of the initial epoch of element synthesis. The star formation rate implied by GRB statistics results in a gamma-ray background that matches the observations more closely than that inferred from other tracers of star formation. This may provide some support for the GRB/SFR-paradigm, which in turn promises a powerful diagnostic of star formation, and thus cosmic chemical evolution, from the era of Population III stars to the present

Magnetohydrodynamic Effects in Propagating Relativistic Ejecta: Reverse Shock and Magnetic Acceleration

We solve the Riemann problem for the deceleration of arbitrarily magnetized relativistic ejecta injected into a static unmagnetized medium. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization s (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when s exceeds a critical value, sc, defined by the balance between the magnetic pressure in the ejecta and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value. This acceleration mechanism is due to the strong magnetic pressure in the ejecta

Scaling analysis of a divergent prefactor in the metastable lifetime of a square-lattice Ising ferromagnet at low temperatures

We examine a square-lattice nearest-neighbor Ising quantum ferromagnet coupled to $d$-dimensional phonon baths. Using the density-matrix equation, we calculate the transition rates between configurations, which determines the specific dynamic. Applying the calculated stochastic dynamic in Monte Carlo simulations, we measure the lifetimes of the metastable state. As the magnetic field approaches $|H|/J=2$ at low temperatures, the lifetime prefactor diverges because the transition rates between certain configurations approaches zero under these conditions. Near $|H|/J=2$ and zero temperature, the divergent prefactor shows scaling behavior as a function of the field, temperature, and the dimension of the phonon baths. With proper scaling, the simulation data at different temperatures and for different dimensions of the baths collapse well onto two master curves, one for $|H|/J>2$ and one for $|H|/J<2$.Comment: published versio

The Supernova Relic Neutrino Background

An upper bound to the supernova relic neutrino background from all past Type II supernovae is obtained using observations of the Universal metal enrichment history. We show that an unambiguous detection of these relic neutrinos by the Super-Kamiokande detector is unlikely. We also analyze the event rate in the Sudbury Neutrino Observatory (where coincident neutrons from anti-nu_e + D --> n + n + e+ might enhance background rejection), and arrive at the same conclusion. If the relic neutrino flux should be observed to exceed our upper bound and if the observations of the metal enrichment history (for z<1) are not in considerable error, then either the Type II supernova rate does not track the metal enrichment history or some mechanism may be responsible for transforming anti-nu_{mu,tau} --> anti-nu_e.Comment: Matches version accepted for publication in Phys. Rev.

Observation of Scaling Violations in Scaled Momentum Distributions at HERA

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of $x$ and $Q^2$ using the ZEUS detector. The evolution of the scaled momentum, $x_p$, with $Q^2,$ in the range 10 to 1280 $GeV^2$, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of $Q^2$.Comment: 21 pages including 4 figures, to be published in Physics Letters B. Two references adde

D* Production in Deep Inelastic Scattering at HERA

This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+$ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.Comment: 17 pages including 4 figure

A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays

The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Lambda_b are selected by the presence of energetic Lambda particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the Lambda particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))% Combined with a previous OPAL measurement, one obtains f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European Physical Journal

Search for Higgs Bosons in e+e- Collisions at 183 GeV

The data collected by the OPAL experiment at sqrts=183 GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54pb-1. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA > 72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European Physical Journal

Time-integrated luminosity recorded by the BABAR detector at the PEP-II e+e- collider

This article is the Preprint version of the final published artcile which can be accessed at the link below.We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the ϒ(4S), ϒ(3S), and ϒ(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e-→e+e- and (for the ϒ(4S) only) e+e-→μ+μ- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross-sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross-sections of e+e-→e+e- and e+e-→μ+μ-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross-sections. For data collected on the ϒ(3S) and ϒ(2S) resonances, an additional uncertainty arises due to ϒ→e+e-X background. For data collected off the ϒ resonances, we estimate an additional uncertainty due to time dependent efficiency variations, which can affect the short off-resonance runs. The relative uncertainties on the luminosities of the on-resonance (off-resonance) samples are 0.43% (0.43%) for the ϒ(4S), 0.58% (0.72%) for the ϒ(3S), and 0.68% (0.88%) for the ϒ(2S).This work is supported by the US Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat à l’Energie Atomique and Institut National de Physique Nucléaire et de Physiquedes Particules (France), the Bundesministerium für Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (The Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Ciencia e Innovación (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation (USA)