Angular Distribution of Decay Leptons from e^+e^- \to W^+W^- at Threshold

The reaction $e^+e^- \to W^+W^-$ produces a $W$-boson pair with a non-trivial spin correlation at threshold. This correlation leads to a characteristic angular correlation between the leptons produced in $W^{\pm} \to \ell ^{\pm} \nu$ (angles relative to the $e^-$ beam direction): $d \sigma /d \cos \theta_+ d \cos \theta_- \sim (1-\cos \theta_+) (1+ \cos \theta_-) (1+\cos \theta_- \cos \theta_+)$ . If only the $\ell^-$ is observed, its angular distribution is $d \sigma / d \cos \theta_- \sim (1+\cos \theta_-)(3-\cos \theta_-)$, implying a forward-backward asymmetry of 3/8. An analytic result is also given for the azimuthal correlation. These results are reproduced by a Monte Carlo program, that also enables us to study the effects of the $W$ decay width. The threshold behaviour, which stems from the dominance of $\nu$-exchange, is contrasted with that due to $\gamma$- and $Z$-exchange, which is relevant for annihilation in the helicity state $e^-_Re^+_L$.Comment: 10 pages, 6 figures, LaTeX, simpler derivation of main results, also added a comparison with Monte Carlo expectation

Investigation of nose bluntness and angle of attack effects on slender bodies in viscous hypersonic flows

Hypersonic flows over cones and straight biconic configurations are calculated for a wide range of free stream conditions in which the gas behind the shock is treated as perfect. Effect of angle of attack and nose bluntness on these slender cones in air is studied extensively. The numerical procedures are based on the solution of complete Navier-Stokes equations at the nose section and parabolized Navier-Stokes equations further downstream. The flow field variables and surface quantities show significant differences when the angle of attack and nose bluntness are varied. The complete flow field is thoroughly analyzed with respect to velocity, temperature, pressure, and entropy profiles. The post shock flow field is studied in detail from the contour plots of Mach number, density, pressure, and temperature. The effect of nose bluntness for slender cones persists as far as 200 nose radii downstream

Glueball Spin

The spin of a glueball is usually taken as coming from the spin (and possibly the orbital angular momentum) of its constituent gluons. In light of the difficulties in accounting for the spin of the proton from its constituent quarks, the spin of glueballs is reexamined. The starting point is the fundamental QCD field angular momentum operator written in terms of the chromoelectric and chromomagnetic fields. First, we look at the restrictions placed on the structure of glueballs from the requirement that the QCD field angular momentum operator should satisfy the standard commutation relationships. This can be compared to the electromagnetic charge/monopole system, where the quantization of the field angular momentum places restrictions (i.e. the Dirac condition) on the system. Second, we look at the expectation value of this operator under some simplifying assumptions.Comment: 11 pages, 0 figures; added references and some discussio

Oxidation of Zr-2.5 Nb Nuclear Reactor Pressure Tubes A New Model

The corrosion and associated deuterium (D) uptake of Zr alloy nuclear reactor pressure tubes have been studied for over 40 years. Zircaloy tubes exhibit rapid D ingress after a period of in-reactor exposure, and have been replaced with tubes fabricated from the more resistant Zr-2.5 wt % Nb alloy. Recently, however, a small percentage of Zr-2.5 Nb tubes have been found to contain high D contents. There is currently no clear understanding of the mechanism for this increased D uptake, and concern exists that an increasing number of high-D tubes will develop with time. A new model for Zr-2.5 Nb corrosion is presented in this paper. The rate of corrosion is shown to be dependent on the rate of transformation of the protective inner oxide layer (closer to the metal) to a porous outer layer. The mechanism of this transformation is not known and should be the subject of future investigations. It is assumed in the model that zirconia chemically dissolves into the solution at the pore bottom. The rate of this dissolution reaction depends on the local pH, which increases if there is a buildup of deuteroxyl ions generated in the cathodic part of the Zr corrosion reaction. A mathematical description of this model, containing several parameters with unknown values, is presented. Assigning certain values to these parameters results in predictions of oxide formation (and thus D buildup) that correspond well with observations.Support of this work by the Atomic Energy Control Board under AECB project no. 2.349.1 is gratefully acknowledged

Pair production and correlated decay of heavy Majorana neutrinos in e+e- collisions

We consider the process e^+e^-\to N_1N_2, where N_1 and N_2 are heavy Majorana particles, with relative CP given by \eta_{CP}=+1 or -1 decaying subsequently via N_1,N_2\to W^{\pm}e^{\mp}. We derive the energy and angle correlation of the dilepton final state, both for like-sign (e^{\mp}e^{\mp}) and unlike-sign (e^-e^+) configurations. Interesting differences are found between the cases \eta_{CP}=+1 and -1. The characteristics of unlike-sign e^+e^- dileptons originating from a Majorana pair N_1N_2 are contrasted with those arising from the reaction e^+e^-\to N\bar{N}\to W^+e^-W^-e^+, where N\bar{N} is a Dirac particle-antiparticle pair

CMB Lensing Power Spectrum Biases from Galaxies and Clusters using High-angular Resolution Temperature Maps

The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to ACT and SPT. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on sigma_8 and an uncertainty on the total neutrino mass of approximately 50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with masses above M_vir = 10^14 M_sun. To achieve such percent level bias, we find that only modes up to a maximum multipole of l_max ~ 2500 should be included in the lensing reconstruction. We also discuss ways to minimize additional bias induced by such aggressive foreground masking by, for example, exploring a two-step masking and in-painting algorithm.Comment: 14 pages, 14 figures, to be submitted to Ap

Bounds on Cross-sections and Lifetimes for Dark Matter Annihilation and Decay into Charged Leptons from Gamma-ray Observations of Dwarf Galaxies

We provide conservative bounds on the dark matter cross-section and lifetime from final state radiation produced by annihilation or decay into charged leptons, either directly or via an intermediate particle $\phi$. Our analysis utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf satellites: HESS observations of Sagittarius and VERITAS observations of Draco, Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the integrals over the dark matter distributions, we find that these constraints are largely unable to rule out dark matter annihilations or decays as an explanation of the PAMELA and ATIC/PPB-BETS excesses. However, if there is an additional Sommerfeld enhancement in dwarfs, which have a velocity dispersion ~10 to 20 times lower than that of the local Galactic halo, then the cross-sections for dark matter annihilating through $\phi$'s required to explain the excesses are very close to the cross-section upper bounds from Willman 1. Dark matter annihilation directly into $\tau$'s is also marginally ruled out by Willman 1 as an explanation of the excesses, and the required cross-section is only a factor of a few below the upper bound from Draco. Finally, we make predictions for the gamma-ray flux expected from the dwarf galaxy Segue 1 for the Fermi Gamma-ray Space Telescope. We find that for a sizeable fraction of the parameter space in which dark matter annihilation into charged leptons explains the PAMELA excess, Fermi has good prospects for detecting a gamma-ray signal from Segue 1 after one year of observation.Comment: 11 pages, 4 figures. References added. Final published versio