4,182 research outputs found
Non-Gaussian wave functionals in Coulomb gauge Yang--Mills theory
A general method to treat non-Gaussian vacuum wave functionals in the
Hamiltonian formulation of a quantum field theory is presented. By means of
Dyson--Schwinger techniques, the static Green functions are expressed in terms
of the kernels arising in the Taylor expansion of the exponent of the vacuum
wave functional. These kernels are then determined by minimizing the vacuum
expectation value of the Hamiltonian. The method is applied to Yang--Mills
theory in Coulomb gauge, using a vacuum wave functional whose exponent contains
up to quartic terms in the gauge field. An estimate of the cubic and quartic
interaction kernels is given using as input the gluon and ghost propagators
found with a Gaussian wave functional.Comment: 27 pages, 21 figure
Octet and Decuplet Baryons in a Confining and Covariant Diquark-Quark Model
We treat baryons as bound states of scalar or axialvector diquarks and a
constituent quark which interact through quark exchange. We obtain fully
four-dimensional wave functions for both octet and decuplet baryons as
solutions of the corresponding Bethe-Salpeter equation. Applications currently
under investigation are: electromagnetic and strong form factors and
strangeness production processes.Comment: 4 pages, 1 figure; talk given by R. Alkofer at PANIC 9
Potencial da fruticultura irrigada nos tabuleiros costeiros.
O Nordeste brasileiro apresenta condicoes excelente para a producao de frutas tropicais de boa qualidade, considerando-se seus aspectos ecologicos, a disponibilidade de area e mao-de-obra, alem das perspectivas favoraveis dos mercados internos e externos de frutas. Por muito tempo, a fruticultura do Nordeste concentrou-se nos Tabuleiros Costeiros, em grande parte situados na Zona da Mata e representando cerca de 8% do territorio nordestino. Nesta regiao, o cultivo de fruteiras e as acoes de pesquisa voltada para a fruticultura tradicionalmente nao lancavam mao da irrigacao. So a partir da decada de 1990 este recurso tecnologico passou a ser usado com frequencia cada vez maior, dada a ocorrencia de um periodo mais ou menos prolongado de deficiencia hidrica duraante a primavera e o verao afetando a produtividade e a vida util dos pomares e a qualidade dos frutos, alem de dificultar o deslocamento da producao para o periodo de entressafra, com precos mais alto para os frutos. Neste trabalho e analisado o potencial da fruticultura irrigada para as regioes dos Tabuleiros Costeiros, a sua viabilidade ecologica e economica, abordando-se tambem a contribuicao do Brasil e do Nordeste para a producao de frutas, as vantagens e os fatores limitantes a fruticultura e as perspectivas de mercado para frutas.bitstream/item/81401/1/Potencial-da-frut-Domingo-Reinhardt-Documentos-69-1996.pd
Heat-kernel expansion and counterterms of the Faddeev-Popov determinant in Coulomb and Landau gauge
The Faddeev-Popov determinant of Landau gauge in d dimensions and Coulomb
gauge in d+1 dimensions is calculated in the heat-kernel expansion up to
next-to-leading order. The UV-divergent parts in d=3,4 are isolated and the
counterterms required for a non-perturbative treatment of the Faddeev-Popov
determinant are determined.Comment: 7 page
Quantum phase space picture of Bose-Einstein Condensates in a double well: Proposals for creating macroscopic quantum superposition states and a study of quantum chaos
We present a quantum phase space model of Bose-Einstein condensate (BEC) in a
double well potential. In a two-mode Fock-state analysis we examine the
eigenvectors and eigenvalues and find that the energy correlation diagram
indicates a transition from a delocalized to a fragmented regime. Phase space
information is extracted from the stationary quantum states using the Husimi
distribution function. It is shown that the quantum states are localized on the
known classical phase space orbits of a nonrigid physical pendulum, and thus
the novel phase space characteristics of a nonrigid physical pendulum such as
the motions are seen to be a property of the exact quantum states. Low
lying states are harmonic oscillator like libration states while the higher
lying states are Schr\"odinger cat-like superpositions of two pendulum rotor
states. To study the dynamics in phase space, a comparison is made between a
displaced quantum wavepacket and the trajectories of a swarm of points in
classical phase space. For a driven double well, it is shown that the classical
chaotic dynamics is manifest in the dynamics of the quantum states pictured
using the Husimi distribution. Phase space analogy also suggests that a
phase displaced wavepacket put on the unstable fixed point on a separatrix will
bifurcate to create a superposition of two pendulum rotor states - a
Schr\"odinger cat state (number entangled state) for BEC. It is shown that the
choice of initial barrier height and ramping, following a phase
imprinting on the condensate, can be used to generate controlled entangled
number states with tunable extremity and sharpness.Comment: revised version, 13 pages, 13 figure
Self-Consistent Pushing and Cranking Corrections to the Meson Fields of the Chiral Quark-Loop Soliton
We study translational and spin-isospin symmetry restoration for the
two-flavor chiral quark-loop soliton. Instead of a static soliton at rest we
consider a boosted and rotating hedgehog soliton. Corrected classical meson
fields are obtained by minimizing a corrected energy functional which has been
derived by semi-classical methods ('variation after projection'). We evaluate
corrected meson fields in the region 300 MeV \le M \le 600 MeV of constituent
quark masses M and compare them with the uncorrected fields. We study the
effect of the corrections on various expectation values of nuclear observables
such as the root-mean square radius, the axial-vector coupling constant,
magnetic moments and the delta-nucleon mass splitting.Comment: 19 pages, LaTeX, 7 postscript figures included using 'psfig.sty', to
appear in Int.J.Mod.Phys.
Determination of gamma-ray widths in N using nuclear resonance fluorescence
The stable nucleus N is the mirror of O, the bottleneck in the
hydrogen burning CNO cycle. Most of the N level widths below the proton
emission threshold are known from just one nuclear resonance fluorescence (NRF)
measurement, with limited precision in some cases. A recent experiment with the
AGATA demonstrator array determined level lifetimes using the Doppler Shift
Attenuation Method (DSAM) in O. As a reference and for testing the
method, level lifetimes in N have also been determined in the same
experiment. The latest compilation of N level properties dates back to
1991. The limited precision in some cases in the compilation calls for a new
measurement in order to enable a comparison to the AGATA demonstrator data. The
widths of several N levels have been studied with the NRF method. The
solid nitrogen compounds enriched in N have been irradiated with
bremsstrahlung. The -rays following the deexcitation of the excited
nuclear levels were detected with four HPGe detectors. Integrated
photon-scattering cross sections of ten levels below the proton emission
threshold have been measured. Partial gamma-ray widths of ground-state
transitions were deduced and compared to the literature. The photon scattering
cross sections of two levels above the proton emission threshold, but still
below other particle emission energies have also been measured, and proton
resonance strengths and proton widths were deduced. Gamma and proton widths
consistent with the literature values were obtained, but with greatly improved
precision.Comment: Final published version, minor grammar changes, 10 pages, 4 figures,
8 tables; An addendum is published where the last section is revised: T.
Sz\"ucs and P. Mohr, Phys. Rev. C 92, 044328 (2015) [arXiv:1510.04956
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