367 research outputs found
Coherent States in Null-Plane Q.E.D
Light front field theories are known to have the usual infra-red divergences
of the equal time theories, as wellas new `spurious' infra-red divergences. The
formar kind of IR divergences are usually treated by giving a small mass to the
gauge particle. An alternative method to deal with these divergences is to
calculate the transition matrix elements in a coherent state basis. In this
paper we present, as a model calculation the lowest order correction to the
three point vertex in QED using a coherent state basis in the light cone
formalism. The relevant transition matrix element is shown to be free of the
true IR divergences up to .Comment: 20 pages and two figures, REVTEX, ITP-SB-93-7
Electrodeposition of zinc-manganese alloy coatings from ionic liquid electrolytes
Electrodeposited zinc-manganese alloys have been found to have potentially
attractive corrosion resisting characteristics for ferrous substrates. However,
researchers have found their formation problematic from aqueous
electrolytes, due particularly to the reactive nature of manganese and its low
reduction potentials. The present investigations examine the possibility of
electrodepositing this alloy utilising an ionic liquid electrolyte. In this manner
electrolytes based upon manganese and zinc chlorides and boric acid were
made by dissolution in a 2:1 molar ratio urea: choline chloride solvent.
Physical measurements of electrolyte characteristics as well as pertinent
electrochemical information on alloy electrodeposition were obtained to
examine the efficacy of this metal/electrolyte combination
The electrodeposition of zinc alloys from ionic liquid electrolytes
Electrodeposited zinc alloys have long been recognised as effective barrier and sacrificial coatings for
ferrous substrates. The effect of alloying zinc with, in the main, more noble metals, has produced
finishes of higher corrosion resistance than simply electrodeposited zinc. In this manner zinc alloys
such as zinc-nickel, zinc-cobalt and zinc-iron are routinely electrodeposited on an industrial scale. A
further zinc alloy, zinc-manganese, has shown a high level of promise in terms of corrosion resistance
but is difficult to electrodeposit from conventional aqueous solutions.
The present investigations are centred around examining the formation of zinc alloys, by
electrodeposition, from non-aqueous ionic liquids. These electrolytes are essentially molten salts
which maintain their liquid state at, or near, to room temperature. Being non-aqueous they are
unlikely to promote significant hydrogen evolution from active metal surfaces - a severe problem for
the electrodeposition of zinc-manganese alloys from aqueous electrolytes. Electrodeposition
conditions for the latter will be discussed in terms of electrolyte types, current density and solution
characteristics such as agitation type and temperature. Zinc-manganese alloy electrodeposits will be
characterised in terms of their composition and morphology. Finally corrosion resistance data will be
presented and this will be compared with other more conventionally deposited zinc alloys
Age Constraints on Brane Models of Dark Energy
Inspired by recent developments in particle physics, the so-called brane
world cosmology seems to provide an alternative explanation for the present
dark energy problem. In this paper, we use the estimated age of high-
objects to constrain the value of the cosmological parameters in some
particular scenarios based on this large scale modification of gravity. We show
that such models are compatible with these observations for values of the
crossover distance between the 4 and 5 dimensions of the order of .Comment: 4 pages, 2 figures, 1 table, to appear in Phys. Rev.
Variable-Speed-of-Light Cosmology from Brane World Scenario
We argue that the four-dimensional universe on the TeV brane of the
Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat,
with gravitons traveling faster than photons instead, while the radion varies
with time. We show that such brane world bimetric model can thereby solve the
flatness and the cosmological constant problems, provided the speed of a
graviton decreases to the present day value rapidly enough. The resolution of
other cosmological problems such as the horizon problem and the monopole
problem requires supplementation by inflation, which may be achieved by the
radion field provided the radion potential satisfies the slow-roll
approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.
Human toxocariasis: contribution by Brazilian researchers
In the present paper the main aspects of the natural history of human infection by Toxocara larvae that occasionally result in the occurrence of visceral and/or ocular larva migrans syndrome were reviewed. The contribution by Brazilian researchers was emphasized, especially the staff of the Tropical Medicine Institute of São Paulo (IMT)
A study of charged kappa in
Based on events collected by BESII, the decay
is studied. In the invariant mass
spectrum recoiling against the charged , the charged
particle is found as a low mass enhancement. If a Breit-Wigner function of
constant width is used to parameterize the kappa, its pole locates at MeV/. Also in this channel,
the decay is observed for the first time.
Its branching ratio is .Comment: 14 pages, 4 figure
Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using
data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000.
The corresponding integrated luminosity is 650 pb^{-1}. The values of the
cross-section obtained are found to be in agreement with QED predictions.
Limits on the anomalous magnetic and electric dipole moments of the tau lepton
are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
- …