3,747 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
Building a path-integral calculus: a covariant discretization approach
Path integrals are a central tool when it comes to describing quantum or
thermal fluctuations of particles or fields. Their success dates back to
Feynman who showed how to use them within the framework of quantum mechanics.
Since then, path integrals have pervaded all areas of physics where fluctuation
effects, quantum and/or thermal, are of paramount importance. Their appeal is
based on the fact that one converts a problem formulated in terms of operators
into one of sampling classical paths with a given weight. Path integrals are
the mirror image of our conventional Riemann integrals, with functions
replacing the real numbers one usually sums over. However, unlike conventional
integrals, path integration suffers a serious drawback: in general, one cannot
make non-linear changes of variables without committing an error of some sort.
Thus, no path-integral based calculus is possible. Here we identify which are
the deep mathematical reasons causing this important caveat, and we come up
with cures for systems described by one degree of freedom. Our main result is a
construction of path integration free of this longstanding problem, through a
direct time-discretization procedure.Comment: 22 pages, 2 figures, 1 table. Typos correcte
Comparison between high-energy proton and charged pion induced damage in Lead Tungstate calorimeter crystals
A Lead Tungstate crystal produced for the electromagnetic calorimeter of the
CMS experiment at the LHC was cut into three equal-length sections. The central
one was irradiated with 290 MeV/c positive pions up to a fluence of (5.67 +-
0.46)x10^13 /cm^2, while the other two were exposed to a 24 GeV/c proton
fluence of (1.17 +- 0.11) x 10^13/ cm^2. The damage recovery in these crystals,
stored in the dark at room temperature, has been followed over two years. The
comparison of the radiation-induced changes in light transmission for these
crystals shows that damage is proportional to the star densities produced by
the irradiation.Comment: 7 pages, 4 figure
First results on radiation damage in PbWO4 crystals exposed to a 20 GeV/c proton beam
We have exposed seven full length production quality crystals of the
electromagnetic calorimeter (ECAL) of the CMS detector to a 20 GeV/c proton
beam at the CERN PS accelerator. The exposure was done at fluxes of 10**12
p/cm**2/h and 10**13 p/cm**2/h and integral fluences of 10**12 p/cm**2 and
10**13 p/cm**2 were reached at both rates. The light transmission of the
crystals was measured after irradiation and suitable cooling time for induced
radioactivity to decrease to a safe level. First results of these measurements
are shown. The possible damage mechanisms are discussed and simulations based
on one possible model are presented. The implications for long-term operation
of CMS are discussed and it is shown that in the whole barrel and at least most
of the ECAL endcap hadron damage alone - even if cumulative - should not cause
the crystals to fail the CMS specification of an induced absorption coefficient
muIND < 1.5 /m during the first 10 years of LHC operation.Comment: 5 pages, to be published in Proc. ICATPP Conference on Astroparticle,
Particle, Space Physics, Detectors and Medical Physics Applications (Como,
Italy, 6 to 10 October 2003
High-energy proton induced damage study of scintillation light output from PbWO4 calorimeter crystals
Eight PbWO4 crystals produced for the electromagnetic calorimeter of the CMS
experiment at LHC have been irradiated in a 20 GeV/c proton beam up to fluences
of 5.4 E13 p/cm2. The damage recovery in these crystals, stored in the dark at
room temperature, has been followed for over a year. Comparative irradiations
with 60Co photons have been performed on seven other crystals using a dose rate
of 1 kGy/h. The issue whether hadrons cause a specific damage to the
scintillation mechanism has been studied through light output measurements on
the irradiated crystals using cosmic rays. The correlation between light output
changes and light transmission changes is measured to be the same for
proton-irradiated crystals and for gamma-irradiated crystals. Thus, within the
precision of the measurements and for the explored range of proton fluences, no
additional, hadron-specific damage to the scintillation mechanism is observed.Comment: 7 pages, 4 figure
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
A study of high-energy proton induced damage in Cerium Fluoride in comparison with measurements in Lead Tungstate calorimeter crystals
A Cerium Fluoride crystal produced during early R&D studies for calorimetry
at the CERN Large Hadron Collider was exposed to a 24 GeV/c proton fluence
Phi_p=(2.78 +- 0.20) x 10EE13 cm-2 and, after one year of measurements tracking
its recovery, to a fluence Phi_p=(2.12 +- 0.15) x 10EE14 cm-2. Results on
proton-induced damage to the crystal and its spontaneous recovery after both
irradiations are presented here, along with some new, complementary data on
proton-damage in Lead Tungstate. A comparison with FLUKA Monte Carlo simulation
results is performed and a qualitative understanding of high-energy damage
mechanism is attempted.Comment: Submitted to Elsevier Science on May 6th, 2010; 11 pages, 8 figure
Thick films of YSZ electrolytes by dip-coating process
Yttria stabilized zirconia (YSZ, 8% Y2O3) thick films were coated on porous Ni-YSZ substrates using the dip-coating process and a suspension with a new formulation. The
suspension was obtained by addition of a polymeric matrix in a stable suspension of a commercial YSZ (Tosoh) powders dispersed in an azeotropic MEK-EtOH mixture. The green layers were densified after an optimization of the suspension composition. YSZ Tosoh particles encapsulated by a zirconium alkoxide sol and added with colloidal alkoxide
precursor are used to load the suspension. The in situ growth of these colloids increases significantly the layers density after an appropriated heat treatment. The obtained films are continuous, homogeneous and 20 ÎŒm thick. Different microstructures are obtained depending on the synthesis parameters of the suspension
On sl(2)-equivariant quantizations
By computing certain cohomology of Vect(M) of smooth vector fields we prove
that on 1-dimensional manifolds M there is no quantization map intertwining the
action of non-projective embeddings of the Lie algebra sl(2) into the Lie
algebra Vect(M). Contrariwise, for projective embeddings sl(2)-equivariant
quantization exists.Comment: 09 pages, LaTeX2e, no figures; to appear in Journal of Nonlinear
Mathematical Physic
- âŠ