301,406 research outputs found
Effective Hamiltonians for holes in antiferromagnets: a new approach to implement forbidden double occupancy
A coherent state representation for the electrons of ordered antiferromagnets
is used to derive effective Hamiltonians for the dynamics of holes in such
systems. By an appropriate choice of these states, the constraint of forbidden
double occupancy can be implemented rigorously. Using these coherent states,
one arrives at a path integral representation of the partition function of the
systems, from which the effective Hamiltonians can be read off. We apply this
method to the t-J model on the square lattice and on the triangular lattice. In
the former case, we reproduce the well-known fermion-boson Hamiltonian for a
hole in a collinear antiferromagnet. We demonstrate that our method also works
for non-collinear antiferromagnets by calculating the spectrum of a hole in the
triangular antiferromagnet in the self-consistent Born approximation and by
comparing it with numerically exact results.Comment: 9 pages, Latex, 6 figure
Subleading Soft Factor for String Disk Amplitudes
We investigate the behavior of superstring disk scattering amplitudes in the
presence of a soft external momentum at finite string tension. We prove that
there are no -corrections to the field theory form of the subleading
soft factor . At the end of this work, we also comment on the
possibility to find the corresponding subleading soft factors in closed string
theory using our result and the KLT relations.Comment: 15 pages, v2: minor changes, new references, version accepted by JHE
Spin-polarized states of nuclear matter
The equations of state of spin-polarized nuclear matter and pure neutron
matter are studied in the framework of the Brueckner-Hartree-Fock theory
including a three-body force. The energy per nucleon calculated
in the full range of spin polarization for symmetric nuclear matter
and pure neutron matter fulfills a parabolic law. In both cases the
spin-symmetry energy is calculated as a function of the baryonic density along
with the related quantities such as the magnetic susceptibility and the Landau
parameter . The main effect of the three-body force is to strongly reduce
the degenerate Fermi gas magnetic susceptibility even more than the value with
only two body force. The EOS is monotonically increasing with the density for
all spin-aligned configurations studied here so that no any signature is found
for a spontaneous transition to a ferromagnetic state.Comment: Contribution to GISELDA Meeting, 14-18 January, 2002 (Frascati), to
appear in World Scientific (Singapore
The role of incident reporting in continuous quality improvement in the intensive care setting
Publisher's copy made available with the permission of the publisherU. Beckman, W.B. Runcimanhttp://www.aaic.net.au/Article.asp?D=199606
Retardation of Particle Evaporation from Excited Nuclear Systems Due to Thermal Expansion
Particle evaporation rates from excited nuclear systems at equilibrium matter
density are studied within the Harmonic-Interaction Fermi Gas Model (HIFGM)
combined with Weisskopf's detailed balance approach. It is found that thermal
expansion of a hot nucleus, as described quantitatively by HIFGM, leads to a
significant retardation of particle emission, greatly extending the validity of
Weisskopf's approach. The decay of such highly excited nuclei is strongly
influenced by surface instabilities
KLEVER: An experiment to measure \boldmath{} at the CERN SPS
The KLEVER experiment aims to measure , supplementing the ongoing NA62 measurement of , to provide new input on CKM unitarity and
potentially new physics. KLEVER is undergoing continuous development, with
particular efforts focused on the design of the target and the beamline. As
described here, adaptations are required relative to the K12 beamline in its
current format, and a series of simulations has been performed to ensure that
an adequate particle flux can be achieved while simultaneously suppressing
problematic backgrounds.Comment: Published under licence CC-BY in Journal of Physics: Conference
Series (JPCS) by IOP Publishing Ltd, proceedings of 6th Symposium on
Prospects in the Physics of Discrete Symmetries, DISCRETE 2018, 26-30 Nov.
2018, Vienna, Austri
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