20,880 research outputs found
The Spin Stiffness and the Transverse Susceptibility of the Half-filled Hubbard Model
The spin stiffness and the transverse susceptibility of the square lattice half-filled Hubbard model are calculated as a
function of the Hubbard parameter ratio by series expansions around the
Ising limit. We find that the calculated spin-stiffness, transverse
susceptibility, and sublattice magnetization for the Hubbard model smoothly
approach the Heisenberg values for large . The results are compared for
different with RPA and other numerical studies.Comment: 9 Revtex pages, 3 Postscript figures, Europhys. Lett. in pres
Linear relations among 4-point functions in the high energy limit of string theory
The decoupling of zero-norm states leads to linear relations among 4-point
functions in the high energy limit of string theory. Recently it was shown that
the linear relations uniquely determine ratios among 4-point functions at the
leading order. The purpose of this paper is to extend the validity of the same
approach to the next-to-leading order and higher orders.Comment: 17 pages, references added, minor modificatio
Blandford-Znajek mechanism in black holes in alternative theories of gravity
According to the Blandford-Znajek mechanism, black hole jets are powered by
the rotational energy of the compact object. In this work, we consider the
possibility that the metric around black holes may not be described by the Kerr
solution and we study how this changes the Blandford-Znajek model. If the
Blandford-Znajek mechanism is responsible for the formation of jets, the
estimate of the jet power in combination with another measurement can test the
nature of black hole candidates and constrain possible deviations from the Kerr
solution. However, this approach might become competitive with respect to other
techniques only when it will be possible to have measurements much more precise
than those available today.Comment: 12 pages, 5 figures. v2: refereed versio
Evolution of Surface Deformations of Weakly-Bound Nuclei in the Continuum
We study weakly-bound deformed nuclei based on the coordinate-space Skyrme
Hartree-Fock-Bogoliubov approach, in which a large box is employed for treating
the continuum and surface diffuseness. Approaching the limit of core-halo
deformation decoupling, calculations found an exotic "egg"-like structure
consisting of a spherical core plus a prolate halo in Ne, in which the
resonant continuum plays an essential role. Generally the halo probability and
the decoupling effect in heavy nuclei are reduced compared to light nuclei, due
to denser level densities around Fermi surfaces. However, deformed halos in
medium-mass nuclei are possible with sparse levels of negative parity, for
example, in Ge. The surface deformations of pairing density
distributions are also influenced by the decoupling effect and are sensitive to
the effective pairing Hamiltonian.Comment: 5 pages and 5 figure
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