8,036 research outputs found
Covariance of Time-Ordered Products Implies Local Commutativity of Fields
We formulate Lorentz covariance of a quantum field theory in terms of
covariance of time-ordered products (or other Green's functions). This
formulation of Lorentz covariance implies spacelike local commutativity or
anticommutativity of fields, sometimes called microscopic causality or
microcausality. With this formulation microcausality does not have to be taken
as a separate assumption.Comment: 6 pages, section on non-local theories removed, published versio
Relations Between Graphs
Given two graphs G and H, we ask under which conditions there is a relation R
that generates the edges of H given the structure of graph G. This construction
can be seen as a form of multihomomorphism. It generalizes surjective
homomorphisms of graphs and naturally leads to notions of R-retractions,
R-cores, and R-cocores of graphs. Both R-cores and R-cocores of graphs are
unique up to isomorphism and can be computed in polynomial time.Comment: accepted by Ars Mathematica Contemporane
Heat transfer and Fourier's law in off-equilibrium systems
We study the most suitable procedure to measure the effective temperature in
off-equilibrium systems. We analyze the stationary current established between
an off-equilibrium system and a thermometer and the necessary conditions for
that current to vanish. We find that the thermometer must have a short
characteristic time-scale compared to the typical decorrelation time of the
glassy system to correctly measure the effective temperature. This general
conclusion is confirmed analyzing an ensemble of harmonic oscillators with
Monte Carlo dynamics as an illustrative example of a solvable model of a glass.
We also find that the current defined allows to extend Fourier's law to the
off-equilibrium regime by consistently defining effective transport
coefficients. Our results for the oscillator model explain why thermal
conductivities between thermalized and frozen degrees of freedom in structural
glasses are extremely small.Comment: 7 pages, REVTeX, 4 eps figure
Comparative Morphology of the Penis and Clitoris in Four Species of Moles (Talpidae).
The penile and clitoral anatomy of four species of Talpid moles (broad-footed, star-nosed, hairy-tailed, and Japanese shrew moles) were investigated to define penile and clitoral anatomy and to examine the relationship of the clitoral anatomy with the presence or absence of ovotestes. The ovotestis contains ovarian tissue and glandular tissue resembling fetal testicular tissue and can produce androgens. The ovotestis is present in star-nosed and hairy-tailed moles, but not in broad-footed and Japanese shrew moles. Using histology, three-dimensional reconstruction, and morphometric analysis, sexual dimorphism was examined with regard to a nine feature masculine trait score that included perineal appendage length (prepuce), anogenital distance, and presence/absence of bone. The presence/absence of ovotestes was discordant in all four mole species for sex differentiation features. For many sex differentiation features, discordance with ovotestes was observed in at least one mole species. The degree of concordance with ovotestes was highest for hairy-tailed moles and lowest for broad-footed moles. In relationship to phylogenetic clade, sex differentiation features also did not correlate with the similarity/divergence of the features and presence/absence of ovotestes. Hairy-tailed and Japanese shrew moles reside in separated clades, but they exhibit a high degree of congruence. Broad-footed and hairy-tailed moles reside within the same clade but had one of the lowest correlations in features and presence/absence of ovotestes. Thus, phylogenetic affinity and the presence/absence of ovotestes are poor predictors for most sex differentiation features within mole external genitalia
Ground-state energy and Wigner crystallization in thick 2D-electron systems
The ground state energy of the 2-D Wigner crystal is determined as a function
of the thickness of the electron layer and the crystal structure. The method of
evaluating the exchange-correlation energy is tested using known results for
the infinitely-thin 2D system. Two methods, one based on the local-density
approximation(LDA), and another based on the constant-density approximation
(CDA) are established by comparing with quantum Monte-Carlo (QMC) results. The
LDA and CDA estimates for the Wigner transition of the perfect 2D fluid are at
and 32 respectively, compared with from QMC. For thick-2D
layers as found in Hetero-junction-insulated-gate field-effect transistors, the
LDA and CDA predictions of the Wigner transition are at and 15.5
respectively. Impurity effects are not considered here.Comment: Last figure and Table are modified in the revised version.
Conclusions regarding the Wigner transition in thick layers are modified in
the revised version. Latex manuscript, four figure
String Gas Baryogenesis
We describe a possible realization of the spontaneous baryogenesis mechanism
in the context of extra-dimensional string cosmology and specifically in the
string gas scenario.Comment: arXiv admin note: substantial text overlap with 0808.0746 by
different autho
Quantum field theory with a fundamental length: A general mathematical framework
We review and develop a mathematical framework for nonlocal quantum field
theory (QFT) with a fundamental length. As an instructive example, we reexamine
the normal ordered Gaussian function of a free field and find the primitive
analyticity domain of its n-point vacuum expectation values. This domain is
smaller than the usual future tube of local QFT, but we prove that in
difference variables, it has the same structure of a tube whose base is the
(n-1)-fold product of a Lorentz invariant region. It follows that this model
satisfies Wightman-type axioms with an exponential high-energy bound which does
not depend on n, contrary to the claims in the literature. In our setting, the
Wightman generalized functions are defined on test functions analytic in the
complex l-neighborhood of the real space, where l is an n-independent constant
playing the role of a fundamental length, and the causality condition is
formulated with the use of an analogous function space associated with the
light cone. In contrast to the scheme proposed by Bruning and Nagamachi [J.
Math. Phys. 45 (2004) 2199] in terms of ultra-hyperfunctions, the presented
theory obviously becomes local as l tends to zero.Comment: 25 pages, v2: updated to match J. Math. Phys. versio
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