4,073 research outputs found
Long range order for lattice dipoles
We consider a system of classical Heisenberg spins on a cubic lattice in
dimensions three or more, interacting via the dipole-dipole interaction. We
prove that at low enough temperature the system displays orientational long
range order, as expected by spin wave theory. The proof is based on reflection
positivity methods. In particular, we demonstrate a previously unproven
conjecture on the dispersion relation of the spin waves, first proposed by
Froehlich and Spencer, which allows one to apply infrared bounds for estimating
the long distance behavior of the spin-spin correlation functions.Comment: 9 page
KMS, etc
A general form of the ``Wick rotation'', starting from imaginary-time Green
functions of quantum-mechanical systems in thermal equilibrium at positive
temperature, is established. Extending work of H. Araki, the role of the KMS
condition and of an associated anti-unitary symmetry operation, the ``modular
conjugation'', in constructing analytic continuations of Green functions from
real- to imaginary times, and back, is clarified.
The relationship between the KMS condition for the vacuum with respect to
Lorentz boosts, on one hand, and the spin-statistics connection and the PCT
theorem, on the other hand, in local, relativistic quantum field theory is
recalled.
General results on the reconstruction of local quantum theories in various
non-trivial gravitational backgrounds from ``Euclidian amplitudes'' are
presented. In particular, a general form of the KMS condition is proposed and
applied, e.g., to the Unruh- and the Hawking effects.
This paper is dedicated to Huzihiro Araki on the occasion of his seventieth
birthday, with admiration, affection and best wishes.Comment: 56 pages, submitted to J. Math. Phy
Spectral Geometry of Heterotic Compactifications
The structure of heterotic string target space compactifications is studied
using the formalism of the noncommutative geometry associated with lattice
vertex operator algebras. The spectral triples of the noncommutative spacetimes
are constructed and used to show that the intrinsic gauge field degrees of
freedom disappear in the low-energy sectors of these spacetimes. The quantum
geometry is thereby determined in much the same way as for ordinary superstring
target spaces. In this setting, non-abelian gauge theories on the classical
spacetimes arise from the K-theory of the effective target spaces.Comment: 14 pages LaTe
Infraparticle Scattering States in Non-Relativistic QED: II. Mass Shell Properties
We study the infrared problem in the usual model of QED with non-relativistic
matter. We prove spectral and regularity properties characterizing the mass
shell of an electron and one-electron infraparticle states of this model. Our
results are crucial for the construction of infraparticle scattering states,
which are treated in a separate paper.Comment: AMS Latex, 45 pages, 2 figure
The Anderson Model as a Matrix Model
In this paper we describe a strategy to study the Anderson model of an
electron in a random potential at weak coupling by a renormalization group
analysis. There is an interesting technical analogy between this problem and
the theory of random matrices. In d=2 the random matrices which appear are
approximately of the free type well known to physicists and mathematicians, and
their asymptotic eigenvalue distribution is therefore simply Wigner's law.
However in d=3 the natural random matrices that appear have non-trivial
constraints of a geometrical origin. It would be interesting to develop a
general theory of these constrained random matrices, which presumably play an
interesting role for many non-integrable problems related to diffusion. We
present a first step in this direction, namely a rigorous bound on the tail of
the eigenvalue distribution of such objects based on large deviation and
graphical estimates. This bound allows to prove regularity and decay properties
of the averaged Green's functions and the density of states for a three
dimensional model with a thin conducting band and an energy close to the border
of the band, for sufficiently small coupling constant.Comment: 23 pages, LateX, ps file available at
http://cpth.polytechnique.fr/cpth/rivass/articles.htm
Expression and alternative splicing of the neural cell adhesion molecule NCAM in human granulosa cells during luteinization
Freshly aspirated human granulosa cells from pre-ovulatory follicles and granulosa cells luteinized in culture possess the neural cell adhesion molecule (NCAM) of approximate molecular mass of 140,000 and NCAM mRNA as confirmed by S1-nuclease protection assays and RT-PCR. Moreover, in the process of luteinization the NCAM isoform pattern is modified. Isoforms containing an insert of 10 amino acids (termed VASE) in the extracellular domain of NCAM were supplemented by alternatively spliced isoforms without this insert. NCAM immunoreactivity, at light and electron microscope levels, was associated with the cell membrane of most granulosa cells which formed clusters. During time in culture an increasing subpopulation of granulosa cells, devoid of NCAM immunoreactivity, spread out and formed monolayers. This differential expression and the alternative splicing of NCAM during luteinization of granulosa cells raise the possibility that NCAM could be involved in folliculogenesis and the formation of the corpus luteum in the human
Response-theory for nonresonant hole burning: Stochastic dynamics
Using non-linear response theory the time signals relevant for nonresonant
spectral hole burning are calculated. The step-reponse function following the
application of a high amplitude ac field (pump) and an intermediate waiting
period is shown to be the sum of the equilibrium integrated response and a
modification due to the preparation via ac irradiation. Both components are
calculated for a class of stochastic dipole reorientation models. The results
indicate that the method can be used for a clearcut distinction of
homogeneously and heterogeneously broadened susceptibilities as they occur in
the relaxation of supercooled liquids or other disordered materials. This is
because only in the heterogeneous case is a frequency selective modification of
the response possible.Comment: revised version, 7 pages, 2 figure
Spin - or, actually: Spin and Quantum Statistics
The history of the discovery of electron spin and the Pauli principle and the
mathematics of spin and quantum statistics are reviewed. Pauli's theory of the
spinning electron and some of its many applications in mathematics and physics
are considered in more detail. The role of the fact that the tree-level
gyromagnetic factor of the electron has the value g = 2 in an analysis of
stability (and instability) of matter in arbitrary external magnetic fields is
highlighted. Radiative corrections and precision measurements of g are
reviewed. The general connection between spin and statistics, the CPT theorem
and the theory of braid statistics are described.Comment: 50 pages, no figures, seminar on "spin
Recommended from our members
Changing European storm loss potentials under modified climate conditions according to ensemble simulations of the ECHAM5/MPI-OM1 GMC
A simple storm loss model is applied to an ensemble of ECHAM5/MPI-OM1 GCM simulations in order to estimate changes of insured loss potentials over Europe in the 21st century. Losses are computed based on the daily maximum wind speed for each grid point. The calibration of the loss model is performed using wind data from the ERA40-Reanalysis and German loss data. The obtained annual losses for the present climate conditions (20C, three realisations) reproduce the statistical features of the historical insurance loss data for Germany.
The climate change experiments correspond to the SRES-Scenarios A1B and A2, and for each of them three realisations are considered. On average, insured loss potentials increase for all analysed European regions at the end of the 21st century. Changes are largest for Germany and France, and lowest for Portugal/Spain. Additionally, the spread between the single realisations is large, ranging e.g. for Germany from −4% to +43% in terms of mean annual loss. Moreover, almost all simulations show an increasing interannual variability of storm damage. This assessment is even more pronounced if no adaptation of building structure to climate change is considered. The increased loss potentials are linked with enhanced values for the high percentiles of surface wind maxima over Western and Central Europe, which in turn are associated with an enhanced number and increased intensity of extreme cyclones over the British Isles and the North Sea
Design of the Pluto Event Generator
We present the design of the simulation package Pluto, aimed at the study of
hadronic interactions at SIS and FAIR energies. Its main mission is to offer a
modular framework with an object-oriented structure, thereby making additions
such as new particles, decays of resonances, new models up to modules for
entire changes easily applicable. Overall consistency is ensured by a plugin-
and distribution manager. Particular features are the support of a modular
structure for physics process descriptions, and the possibility to access the
particle stream for on-line modifications. Additional configuration and
self-made classes can be attached by the user without re-compiling the package,
which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High
Energy and Nuclear Physic
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