1,296 research outputs found
On the characterization of isotropic Gaussian fields on homogeneous spaces of compact groups
Let T be a random field invariant under the action of a compact group G We
give conditions ensuring that independence of the random Fourier coefficients
is equivalent to Gaussianity. As a consequence, in general it is not possible
to simulate a non-Gaussian invariant random field through its Fourier expansion
using independent coefficients
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An empirical investigation of the relationship between market share and the competitive market position of a firm.
Van der Waerden calculus with commuting spinor variables and the Hilbert-Krein structure of the superspace
Working with anticommuting Weyl(or Mayorana) spinors in the framework of the
van der Waerden calculus is standard in supersymmetry. The natural frame for
rigorous supersymmetric quantum field theory makes use of operator-valued
superdistributions defined on supersymmetric test functions. In turn this makes
necessary a van der Waerden calculus in which the Grassmann variables
anticommute but the fermionic components are commutative instead of being
anticommutative. We work out such a calculus in view of applications to the
rigorous conceptual problems of the N=1 supersymmetric quantum field theory.Comment: 14 page
A quantum logical and geometrical approach to the study of improper mixtures
We study improper mixtures from a quantum logical and geometrical point of
view. Taking into account the fact that improper mixtures do not admit an
ignorance interpretation and must be considered as states in their own right,
we do not follow the standard approach which considers improper mixtures as
measures over the algebra of projections. Instead of it, we use the convex set
of states in order to construct a new lattice whose atoms are all physical
states: pure states and improper mixtures. This is done in order to overcome
one of the problems which appear in the standard quantum logical formalism,
namely, that for a subsystem of a larger system in an entangled state, the
conjunction of all actual properties of the subsystem does not yield its actual
state. In fact, its state is an improper mixture and cannot be represented in
the von Neumann lattice as a minimal property which determines all other
properties as is the case for pure states or classical systems. The new lattice
also contains all propositions of the von Neumann lattice. We argue that this
extension expresses in an algebraic form the fact that -alike the classical
case- quantum interactions produce non trivial correlations between the
systems. Finally, we study the maps which can be defined between the extended
lattice of a compound system and the lattices of its subsystems.Comment: submitted to the Journal of Mathematical Physic
The Minkowski and conformal superspaces
We define complex Minkowski superspace in 4 dimensions as the big cell inside
a complex flag supermanifold. The complex conformal supergroup acts naturally
on this super flag, allowing us to interpret it as the conformal
compactification of complex Minkowski superspace. We then consider real
Minkowski superspace as a suitable real form of the complex version. Our
methods are group theoretic, based on the real conformal supergroup and its
Lie superalgebra.Comment: AMS LaTeX, 44 page
On SUSY curves
In this note we give a summary of some elementary results in the theory of
super Riemann surfaces (SUSY curves)
On a certain class of semigroups of operators
We define an interesting class of semigroups of operators in Banach spaces,
namely, the randomly generated semigroups. This class contains as a remarkable
subclass a special type of quantum dynamical semigroups introduced by
Kossakowski in the early 1970s. Each randomly generated semigroup is
associated, in a natural way, with a pair formed by a representation or an
antirepresentation of a locally compact group in a Banach space and by a
convolution semigroup of probability measures on this group. Examples of
randomly generated semigroups having important applications in physics are
briefly illustrated.Comment: 11 page
Charge Order Superstructure with Integer Iron Valence in Fe2OBO3
Solution-grown single crystals of Fe2OBO3 were characterized by specific
heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific
heat at 340 K indicates the onset of charge order. Evidence for a doubling of
the unit cell at low temperature is presented. Combining structural refinement
of diffraction data and Mossbauer spectra, domains with diagonal charge order
are established. Bond-valence-sum analysis indicates integer valence states of
the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest
example of ionic charge order so far.Comment: 4 pages, 5 figures. Fig. 3 is available in higher resolution from the
authors. PRL in prin
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