Smooth vortex precession in superfluid 4He

We have measured a precessing superfluid vortex line, stretched from a wire to the wall of a cylindrical cell. By contrast to previous experiments with a similar geometry, the motion along the wall is smooth. The key difference is probably that our wire is substantially off center. We verify several numerical predictions about the motion, including an asymmetry in the precession signature, the behavior of pinning events, and the temperature dependence of the precession.Comment: 8 pages, 8 figure

Adjoint "quarks" on coarse anisotropic lattices: Implications for string breaking in full QCD

A detailed study is made of four dimensional SU(2) gauge theory with static adjoint ``quarks'' in the context of string breaking. A tadpole-improved action is used to do simulations on lattices with coarse spatial spacings $a_s$, allowing the static potential to be probed at large separations at a dramatically reduced computational cost. Highly anisotropic lattices are used, with fine temporal spacings $a_t$, in order to assess the behavior of the time-dependent effective potentials. The lattice spacings are determined from the potentials for quarks in the fundamental representation. Simulations of the Wilson loop in the adjoint representation are done, and the energies of magnetic and electric ``gluelumps'' (adjoint quark-gluon bound states) are calculated, which set the energy scale for string breaking. Correlators of gauge-fixed static quark propagators, without a connecting string of spatial links, are analyzed. Correlation functions of gluelump pairs are also considered; similar correlators have recently been proposed for observing string breaking in full QCD and other models. A thorough discussion of the relevance of Wilson loops over other operators for studies of string breaking is presented, using the simulation results presented here to support a number of new arguments.Comment: 22 pages, 14 figure

Milagro limits and HAWC sensitivity for the rate-density of evaporating Primordial Black Holes

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Observation of quantized circulation in rotating superfluid /sup 4/He

The quantized circulation of rotating superfluid helium 4 was measured by monitoring the time rate of precession of the plane of vibration of a vibrating wire lying along the cylindrical axis of the container. (GHT

OBSERVATION OF QUANTUM STEPS IN THE SUPERFLUID CIRCULATION AROUND A FINE WIRE IN LIQUID 4He II IN ROTATION

Nous avons mesuré par la méthode de Vinen la circulation superfluide autour d'un fil fin dans l'hélium II à ~ 0,4 K en fonction de la vitesse angulaire de rotation de l'appareil. Ces résultats présentent l'évidence définitive d'étapes de circulation quantique. Cependant, la grandeur de l'étape observée a varié d'une expérience à l'autre.Measurements by the Vinen method of the superfluid circulation aroud a 25 µm diameter wire in liquid helium II at ~ 0.4 K as a function of angular velocity of rotation of the apparatus show clear evidence for quantum steps in the range of ± 4 quantum units. However, the observed size of the circulation step has varied from run to run

Sensitivity of the high altitude water Cherenkov detector to sources of multi-TeV gamma rays

The High Altitude Water Cherenkov (HAWC) observatory is an array of large water Cherenkov detectors sensitive to gamma rays and hadronic cosmic rays in the energy band between 100 GeV and 100 TeV. The observatory will be used to measure high-energy protons and cosmic rays via detection of the energetic secondary particles reaching the ground when one of these particles interacts in the atmosphere above the detector. HAWC is under construction at a site 4100 meters above sea level on the northern slope of the volcano Sierra Negra, which is located in central Mexico at 19 N latitude. It is scheduled for completion in 2014. In this paper we estimate the sensitivity of the HAWC instrument to point-like and extended sources of gamma rays. The source fluxes are modeled using both unbroken power laws and power laws with exponential cutoffs. HAWC, in one year, is sensitive to point sources with integral power-law spectra as low as 5×10-13 cm-2sec-1 above 2 TeV (approximately 50 mCrab) over 5 sr of the sky. This is a conservative estimate based on simple event parameters and is expected to improve as the data analysis techniques are refined. We discuss known TeV sources and the scientific contributions that HAWC can make to our understanding of particle acceleration in these sources. © 2013 Elsevier B.V. All rights reserved