53,848 research outputs found
Fermions in the pseudoparticle approach
The pseudoparticle approach is a numerical technique to compute path
integrals without discretizing spacetime. The basic idea is to integrate over
those field configurations, which can be represented by a sum of a fixed number
of localized building blocks (pseudoparticles). In a couple of previous papers
we have successfully applied the pseudoparticle approach to pure SU(2)
Yang-Mills theory. In this work we discuss how to incorporate fermionic fields
in the pseudoparticle approach. To test our method, we compute the phase
diagram of the 1+1-dimensional Gross-Neveu model in the large-N limit.Comment: 11 pages, 10 figure
A formal theory of cubical complexes Formal report, 1 Sep. 1968 - 30 Apr. 1969
Algorithm for computation of test failures in cyclic circuit
The Dynamics of Child Poverty: Britain and Germany Compared
We compare patterns of movements into and out of poverty by children in Britain and Germany using data from the British Household Panel Survey and the German Socio- Economic Panel for the period 1992-7. Compared to Germany, in Britain poverty persistence is greater, and poverty exit rates in particular are lower. In both countries poverty is particularly persistent among children in lone parent households and households with a nonworking head. Events such as family formation and dissolution, and changes in household labour market attachment are associated with child poverty transitions in the direction expected, and in both countries. However a large fraction of the observed poverty transitions are not accounted for by these events.
Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial Films in Fields up to 50 T''
Recently Wagner et al. [Phys. Rev. Lett. Vol. 81, P. 3980 (1998)] proposed
that Mott's original model be modified to incorporate a hopping barrier which
depends on the misorientation between the spins of electrons at the initial and
the final states in an elementary process. They further claimed that using the
model they can explain the observed scaling behavior--
negative-magnetoresistivity scaling proportional to the Brillouin function
in the ferromagnetic state and to in the paramagnetic
state. In this comment we argue that the modification needed for Mott's
original model is different from that proposed by Wagner et al. and further
show that our picture will successfully explain the observed scaling in the two
regimes.Comment: 1 pag
Bose-Einstein condensates with attractive 1/r interaction: The case of self-trapping
Amplifying on a proposal by O'Dell et al. for the realization of
Bose-Einstein condensates of neutral atoms with attractive interaction,
we point out that the instance of self-trapping of the condensate, without
external trap potential, is physically best understood by introducing
appropriate "atomic" units. This reveals a remarkable scaling property: the
physics of the condensate depends only on the two parameters and
, where is the particle number, the scattering length,
the "Bohr" radius and the trap frequency in atomic units. We
calculate accurate numerical results for self-trapping wave functions and
potentials, for energies, sizes and peak densities, and compare with previous
variational results. As a novel feature we point out the existence of a second
solution of the extended Gross-Pitaevskii equation for negative scattering
lengths, with and without trapping potential, which is born together with the
ground state in a tangent bifurcation. This indicates the existence of an
unstable collectively excited state of the condensate for negative scattering
lengths.Comment: 7 pages, 7 figures, to appear in Phys. Rev.
Modeling Pressure-Ionization of Hydrogen in the Context of Astrophysics
The recent development of techniques for laser-driven shock compression of
hydrogen has opened the door to the experimental determination of its behavior
under conditions characteristic of stellar and planetary interiors. The new
data probe the equation of state (EOS) of dense hydrogen in the complex regime
of pressure ionization. The structure and evolution of dense astrophysical
bodies depend on whether the pressure ionization of hydrogen occurs
continuously or through a ``plasma phase transition'' (PPT) between a molecular
state and a plasma state. For the first time, the new experiments constrain
predictions for the PPT. We show here that the EOS model developed by Saumon
and Chabrier can successfully account for the data, and we propose an
experiment that should provide a definitive test of the predicted PPT of
hydrogen. The usefulness of the chemical picture for computing astrophysical
EOS and in modeling pressure ionization is discussed.Comment: 16 pages + 4 figures, to appear in High Pressure Researc
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