636 research outputs found
Equivariant quantization of orbifolds
Equivariant quantization is a new theory that highlights the role of
symmetries in the relationship between classical and quantum dynamical systems.
These symmetries are also one of the reasons for the recent interest in
quantization of singular spaces, orbifolds, stratified spaces... In this work,
we prove existence of an equivariant quantization for orbifolds. Our
construction combines an appropriate desingularization of any Riemannian
orbifold by a foliated smooth manifold, with the foliated equivariant
quantization that we built in \cite{PoRaWo}. Further, we suggest definitions of
the common geometric objects on orbifolds, which capture the nature of these
spaces and guarantee, together with the properties of the mentioned foliated
resolution, the needed correspondences between singular objects of the orbifold
and the respective foliated objects of its desingularization.Comment: 13 page
Equivariant symbol calculus for differential operators acting on forms
We prove the existence and uniqueness of a projectively equivariant symbol
map (in the sense of Lecomte and Ovsienko) for the spaces of differential
operators transforming p-forms into functions. These results hold over a smooth
manifold endowed with a flat projective structure.
As an application, we classify the Vect(M)-equivariant maps from to
over any manifold M, recovering and improving earlier results by N.
Poncin. This provides the complete answer to a question raised by P. Lecomte
about the extension of a certain intrinsic homotopy operator.Comment: 14 page
The space of m-ary differential operators as a module over the Lie algebra of vector fields
The space of m-ary differential operators acting on weighted densities is a
(m+1)-parameter family of modules over the Lie algebra of vector fields. For
almost all the parameters, we construct a canonical isomorphism between this
space and the corresponding space of symbols as sl(2)-modules. This yields to
the notion of the sl(2)-equivariant symbol calculus for m-ary differential
operators. We show, however, that these two modules cannot be isomorphic as
sl(2)-modules for some particular values of the parameters. Furthermore, we use
the symbol map to show that all modules of second-order m-ary differential
operators are isomorphic to each other, except for few modules called singular.Comment: 20 pages; LaTeX2e; minor correction
A First Approximation for Quantization of Singular Spaces
Many mathematical models of physical phenomena that have been proposed in
recent years require more general spaces than manifolds. When taking into
account the symmetry group of the model, we get a reduced model on the
(singular) orbit space of the symmetry group action. We investigate
quantization of singular spaces obtained as leaf closure spaces of regular
Riemannian foliations on compact manifolds. These contain the orbit spaces of
compact group actions and orbifolds. Our method uses foliation theory as a
desingularization technique for such singular spaces. A quantization procedure
on the orbit space of the symmetry group - that commutes with reduction - can
be obtained from constructions which combine different geometries associated
with foliations and new techniques originated in Equivariant Quantization. The
present paper contains the first of two steps needed to achieve these just
detailed goals.Comment: 30 page
Decomposition of symmetric tensor fields in the presence of a flat contact projective structure
Let be an odd-dimensional Euclidean space endowed with a contact 1-form
. We investigate the space of symmetric contravariant tensor fields on
as a module over the Lie algebra of contact vector fields, i.e. over the
Lie subalgebra made up by those vector fields that preserve the contact
structure. If we consider symmetric tensor fields with coefficients in tensor
densities, the vertical cotangent lift of contact form is a contact
invariant operator. We also extend the classical contact Hamiltonian to the
space of symmetric density valued tensor fields. This generalized Hamiltonian
operator on the symbol space is invariant with respect to the action of the
projective contact algebra . The preceding invariant operators lead
to a decomposition of the symbol space (expect for some critical density
weights), which generalizes a splitting proposed by V. Ovsienko
Projectively equivariant quantizations over the superspace
We investigate the concept of projectively equivariant quantization in the
framework of super projective geometry. When the projective superalgebra
pgl(p+1|q) is simple, our result is similar to the classical one in the purely
even case: we prove the existence and uniqueness of the quantization except in
some critical situations. When the projective superalgebra is not simple (i.e.
in the case of pgl(n|n)\not\cong sl(n|n)), we show the existence of a
one-parameter family of equivariant quantizations. We also provide explicit
formulas in terms of a generalized divergence operator acting on supersymmetric
tensor fields.Comment: 19 page
Analysis by in Situ Hybridization of Cells Expressing mRNA for Tumor-Necrosis Factor in the Developing Thymus of Mice
We have used in situ hybridization to investigate the expression of TNF-α genes by
thymic cells during fetal development in mice. In 14-day-old fetal thymuses, very scarce
cells produce TNF-α mRNA. A second phase of cytokine gene expression starts on day
16. The density of positive cells progressively increases up to day 20. Thymuses at 15
days of gestation and after birth do not express detectable cytokine mRNA. In an
attempt to identify the nature of the TNF-α mRNA-producing cells, acid phosphatase
activity, which is characteristic of the macrophage lineage, was studied in the same
thymuses. Acid phosphatase-positive cells only appear on day 15. Their frequency
increases up to birth. However, no correlation can be established between acid
phosphatase—and TNFα mRNA— positive cells. The results indicate that a small subset
of thymic cells is responsible for TNF-α mRNA production during ontogeny: These cells
are not yet identified. The possible role of TNF-α in thymic ontogeny is discussed
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