25,592 research outputs found
Axiom System and Completeness Expression for Quantum Mechanics
The standard axiomatization of quantum mechanics (QM) is not fully explicit
about the role of the time-parameter. Especially, the time reference within the
probability algorithm (the Born Rule, BR) is unclear. Using a plausible
principle P1, about the role of probability in a physical theory, and a second
principle P2 affording a most natural way to make BR precise, a logical
conflict with the standard expression for the completeness of QM can be
derived. Rejecting P1 is implausible. Rejecting P2 leads to unphysical results
and to a conflict with a generalization of P2, a principle P3. It is thus made
plausible that the standard expression of QM completeness must be revised. An
absolutely explicit form of the axioms is provided, including a precise form of
the projection postulate. An appropriate expression for QM completeness,
reflecting the restrictions of the Gleason and Kochen-Specker theorems is
proposed.Comment: 20 pages, no figure
Localization of strongly correlated electrons as Jahn-Teller polarons in manganites
A realistic modeling of manganites should include the Coulomb repulsion
between electrons, the Hund's rule coupling to spins, and
Jahn-Teller phonons. Solving such a model by dynamical mean field theory, we
report large magnetoresistances and spectra in good agreement with experiments.
The physics of the unusual, insulating-like paramagnetic phase is determined by
correlated electrons which are-due to strong correlations-easily trapped as
Jahn-Teller polarons.Comment: 4 pages, 3 figure
Dwarf galaxies in the Local Group: the VLT perspective
Recent results on the evolution of Local Group dwarf galaxies obtained from
VLT imaging and spectroscopy are briefly reviewed, and prospects for dwarf
galaxy research at the VLT are discussed in the light of the current and
forthcoming instrumentation. Some aspects of future instrument developments,
such as deep wide-field imaging at both optical and near-infrared wavelengths
that may be of advantage for research on the evolution of dwarf galaxies, are
briefly discussed.Comment: 6 pages, 3 figures. To be published in the Proceedings of the ESO
Workshop Scientific Drivers for ESO Future VLT/VLTI Instrumentation, J.
Bergeron and G. Monnet, Eds., Springer Verlag 200
Microscopic conditions favoring itinerant ferromagnetism: Hund's rule coupling and orbital degeneracy
The importance of Hund's rule coupling for the stabilization of itinerant
ferromagnetism is investigated within a two-band Hubbard model. The magnetic
phase diagram is calculated by finite-temperature quantum Monte Carlo
simulations within the dynamical mean-field theory. Ferromagnetism is found in
a broad range of electron fillings whereas antiferromagnetism exists only near
half filling. The possibility of orbital ordering at quarter filling is also
analyzed.Comment: 5 pages, 6 figures, RevTeX, final version contains an additional
phase diagram for smaller Hund's rule coupling. to appear in Eur. Phys. J. B
(1998
Higgs stability-bound and fermionic dark matter
Higgs-portal interactions of fermionic dark matter -- in contrast to fermions
coupled via Yukawa interactions -- can have a stabilizing effect on the
standard-model Higgs potential. A non-perturbative renormalization-group
analysis reveals that, similar to higher-order operators in the Higgs potential
itself, the fermionic portal coupling can increase the metastability scale by
only about one order of magnitude. Furthermore, this regime of very weakly
coupled dark matter is in conflict with relic-density constraints. Conversely,
fermionic dark matter with the right relic abundance requires either a low
cutoff scale of the effective field theory or a strongly interacting scalar
sector. This results in a triviality problem in the scalar sector which
persists at the non-perturbative level. The corresponding breakdown of the
effective field theory suggests a larger dark sector to be present not too far
above the dark-fermion mass-scale.Comment: 12 pages; 3 figure
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