438 research outputs found
Scalar-gauge dynamics in (2+1) dimensions at small and large scalar couplings
We present the results of a detailed calculation of the excitation spectrum
of states with quantum numbers J^{PC}=0++, 1-- and 2++ in the three-dimensional
SU(2) Higgs model at two values of the scalar self-coupling and for fixed gauge
coupling. In the context of studies of the electroweak phase transition at
finite temperature these couplings correpond to tree-level, zero temperature
Higgs masses of 35 GeV and 120 GeV, respectively. We also study the properties
of Polyakov loop operators, which serve to test the confining properties of the
model in the symmetric phase. At both values of the scalar coupling we obtain
masses of bound states consisting entirely of gauge degrees of freedom
("W-balls"), which are very close to those obtained in the pure gauge theory.
We conclude that the previously observed, approximate decoupling of the scalar
and gauge sectors of the theory persists at large scalar couplings. We study
the crossover region at large scalar coupling and present a scenario how the
confining properties of the model in the symmetric phase are lost inside the
crossover by means of flux tube decay. We conclude that the underlying dynamics
responsible for the observed dense spectrum of states in the Higgs region at
large couplings must be different from that in the symmetric phase.Comment: 36 pages, LaTeX, 13 postscript files, to be included with epsf;
improved presentation, updated references, conclusions unchanged; version to
appear in Nucl. Phys.
Detailed Phase Transition Study at M_H <= 70 GeV in a 3-dimensional --Higgs Model
We study the electroweak phase transition in an effective 3-dimensional
theory for a Higgs mass of about 70 GeV by Monte Carlo simulations. The
transition temperature and jumps of order parameters are obtained and
extrapolated to the continuum using multi-histogram techniques and finite size
analysis.Comment: Talk presented at LATTICE96(electroweak), 4 pages, 5 figure
A lattice determination of g_A and <x> from overlap fermions
We present results for the nucleon's axial charge g_A and the first moment
of the unpolarized parton distribution function from a simulation of
quenched overlap fermions.Comment: Talk presented at Lattice2004(chiral), 4 pages, 4 figure
Physics of the Electroweak Phase Transition at M_H <= 70 GeV in a 3-dimensional SU(2)-Higgs Model
Physical parameters of the electroweak phase transition in a 3d effective
lattice SU(2)-Higgs model are presented. The phase transition temperatures,
latent heats and continuum condensate discontinuities are measured at Higgs
masses of about 70 and 35 GeV. Masses and Higgs condensates are compared to
perturbation theory in the broken phase. In the symmetric phase bound states
and the static force are determined.Comment: Talk presented at LATTICE96(electroweak), 4 pages, 5 figure
The costs of preventing and treating chagas disease in Colombia
Background: The objective of this study is to report the costs of Chagas disease in Colombia, in terms of vector disease control programmes and the costs of providing care to chronic Chagas disease patients with cardiomyopathy.
Methods: Data were collected from Colombia in 2004. A retrospective review of costs for vector control programmes carried out in rural areas included 3,084 houses surveyed for infestation with triatomine bugs and 3,305 houses sprayed with insecticide. A total of 63 patient records from 3 different hospitals were selected for a retrospective review of resource use. Consensus methodology with local experts was used to estimate care seeking behaviour and to complement observed data on utilisation. Findings: The mean cost per house per entomological survey was of 2004), whereas the mean cost of spraying a house with insecticide was 46.4 and 1,028, whereas lifetime costs averaged $11,619 per patient. Chronic Chagas disease patients have limited access to healthcare, with an estimated 22% of patients never seeking care. Conclusion: Chagas disease is a preventable condition that affects mostly poor populations living in rural areas. The mean costs of surveying houses for infestation and spraying infested houses were low in comparison to other studies and in line with treatment costs. Care seeking behaviour and the type of insurance affiliation seem to play a role in the facilities and type of care that patients use, thus raising concerns about equitable access to care. Preventing Chagas disease in Colombia would be cost-effective and could contribute to prevent inequalities in health and healthcare.Wellcome Trus
Renormalisation of one-link quark operators for overlap fermions with L\"uscher-Weisz gauge action
We compute lattice renormalisation constants of one-link quark operators
({\it i.e.} operators with one covariant derivative) for overlap fermions and
L\"uscher-Weisz gauge action in one-loop perturbation theory. Among others,
such operators enter the calculation of moments of polarised and unpolarised
hadron structure functions. Results are given for \beta=8.45, \beta=8.0 and
mass parameter \rho=1.4, which are commonly used in numerical simulations. We
apply mean field (tadpole) improvement to our results.Comment: 13 pages, 1 figur
Photoionization of helium atoms irradiated with intense vacuum ultraviolet free-electron laser light. Part I. Experimental study of multiphoton and single-photon processes
Sem informaçãoThe interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with 100 fs pulses at 95 nm wavelength, which corresponds to similar to 13 eV photon energy. The ionization of He atoms is observed at a peak intensity of 10(10)-10(13) W/cm(2), which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schrodinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at 15.4 eV is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and He+ time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.The interaction of He atoms with intense vacuum-ultraviolet light of a free-electron laser is investigated using time-of-flight mass spectroscopy and photoelectron spectroscopy. The atoms were irradiated with 100 fs pulses at 95 nm wavelength, which corresponds to similar to 13 eV photon energy. The ionization of He atoms is observed at a peak intensity of 10(10)-10(13) W/cm(2), which is due both to nonlinear multiphoton ionization with the fundamental wavelength and single-photon ionization with third harmonic radiation of the free-electron laser. The observation of two sharp photoelectron peaks in the kinetic energy spectra, that are separated by the photon energy, is in agreement with the numerical solution of the time-dependent Schrodinger equation. The calculation was done using the fully quantized field and a limited but representative set of basis states. The ionization rate dependence on the laser peak intensity indicates that: (a) The low-energy peak in the photoelectron spectra is mainly due to two-photon absorption of the fundamental, but (b) the high-energy peak at 15.4 eV is probably due to third harmonic FEL radiation. The theoretically predicted contribution from three-photon absorption of the fundamental is of about the same order of magnitude and could not be separated from the third harmonic background signal. Particularly, the photoelectron spectra and He+ time-of-flight data give evidence that the intensity of third harmonic light is high enough to perform single-shot spectroscopy on gas phase samples.72218Sem informaçãoSem informaçãoSem informaçãoWe thank A. Swiderski for technical support in the design and construction of the experiment and the TTF team at DESY for running the accelerator, working on the FEL and the photon diagnostics. This work was supported by the DFG
Multiple ionization of rare gas atoms irradiated with intense VUV radiation
Sem informaçãoThe interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated. The ionization products of xenon and argon atomic beams are analyzed with time-of-flight mass spectroscopy. At 98 nm wavelength and similar to10(13) W/cm(2) multiple charged ions up to Xe6+ (Ar4+) are detected. From the intensity dependence of multiple charged ion yields the mechanisms of multiphoton processes were derived. In the range of similar to10(12)-10(13) W/cm(2) the ionization is attributed to sequential multiphoton processes. The production of multiple charged ions saturates at 5-30 times lower power densities than at 193 and 564 nm wavelength, respectively.The interaction of intense vacuum-ultraviolet radiation from a free-electron laser with rare gas atoms is investigated. The ionization products of xenon and argon atomic beams are analyzed with time-of-flight mass spectroscopy. At 98 nm wavelength and similar to10(13) W/cm(2) multiple charged ions up to Xe6+ (Ar4+) are detected. From the intensity dependence of multiple charged ion yields the mechanisms of multiphoton processes were derived. In the range of similar to10(12)-10(13) W/cm(2) the ionization is attributed to sequential multiphoton processes. The production of multiple charged ions saturates at 5-30 times lower power densities than at 193 and 564 nm wavelength, respectively.94214Sem informaçãoSem informaçãoSem informaçãoWe thank A. Swiderski for technical support in the design and construction of the cluster experiment and the TTF team at DESY for providing the FEL beam and the photon diagnostics. One of the authors (H.W.) is grateful to Peter Lambropoulos for helpful comments. In addition, we thank R. Santra for making calculations available prior to publication
- …