7,558 research outputs found
Coisotropic submanifolds in Poisson geometry and branes in the Poisson sigma model
General boundary conditions ("branes") for the Poisson sigma model are
studied. They turn out to be labeled by coisotropic submanifolds of the given
Poisson manifold. The role played by these boundary conditions both at the
classical and at the perturbative quantum level is discussed. It turns out to
be related at the classical level to the category of Poisson manifolds with
dual pairs as morphisms and at the perturbative quantum level to the category
of associative algebras (deforming algebras of functions on Poisson manifolds)
with bimodules as morphisms. Possibly singular Poisson manifolds arising from
reduction enter naturally into the picture and, in particular, the construction
yields (under certain assumptions) their deformation quantization.Comment: 21 pages, 2 figures; minor corrections, references updated; final
versio
Loop and Path Spaces and Four-Dimensional BF Theories: Connections, Holonomies and Observables
We study the differential geometry of principal G-bundles whose base space is
the space of free paths (loops) on a manifold M. In particular we consider
connections defined in terms of pairs (A,B), where A is a connection for a
fixed principal bundle P(M,G) and B is a 2-form on M. The relevant curvatures,
parallel transports and holonomies are computed and their expressions in local
coordinates are exhibited. When the 2-form B is given by the curvature of A,
then the so-called non-abelian Stokes formula follows.
For a generic 2-form B, we distinguish the cases when the parallel transport
depends on the whole path of paths and when it depends only on the spanned
surface. In particular we discuss generalizations of the non-abelian Stokes
formula. We study also the invariance properties of the (trace of the) holonomy
under suitable transformation groups acting on the pairs (A,B).
In this way we are able to define observables for both topological and
non-topological quantum field theories of the BF type. In the non topological
case, the surface terms may be relevant for the understanding of the
quark-confinement problem. In the topological case the (perturbative)
four-dimensional quantum BF-theory is expected to yield invariants of imbedded
(or immersed) surfaces in a 4-manifold M.Comment: TeX, 39 page
Radiation Hardness tests with neutron flux on different Silicon photomultiplier devices
Radiation hardness is an important requirement for solid state readout
devices operating in high radiation environments common in particle physics
experiments. The MEGII experiment, at PSI, Switzerland, investigates the
forbidden decay . Exploiting the most intense
muon beam of the world. A significant flux of non-thermal neutrons (kinetic
energy ) is present in the experimental hall produced along
the beamline and in the hall itself. We present the effects of neutron fluxes
comparable to the MEGII expected doses on several Silicon PhotoMulitpliers
(SiPMs). The tested models are: AdvanSiD ASD-NUV3S-P50 (used in MEGII
experiment), AdvanSiD ASD-NUV3S-P40, AdvanSiD ASD-RGB3S-P40, Hamamatsu and
Excelitas C30742-33-050-X. The neutron source is the thermal Sub-critical
Multiplication complex (SM1) moderated with water, located at the University of
Pavia (Italy). We report the change of SiPMs most important electric
parameters: dark current, dark pulse frequency, gain, direct bias resistance,
as a function of the integrated neutron fluency.Comment: 9 pages, 6 figures. Proceedings from Instrumentation for colliding
Beam Physics (INSTR-17) 27-02-2017/03-03-2017 Novosibirsk (R
Four-Dimensional Yang-Mills Theory as a Deformation of Topological BF Theory
The classical action for pure Yang--Mills gauge theory can be formulated as a
deformation of the topological theory where, beside the two-form field
, one has to add one extra-field given by a one-form which transforms
as the difference of two connections. The ensuing action functional gives a
theory that is both classically and quantistically equivalent to the original
Yang--Mills theory. In order to prove such an equivalence, it is shown that the
dependency on the field can be gauged away completely. This gives rise
to a field theory that, for this reason, can be considered as semi-topological
or topological in some but not all the fields of the theory. The symmetry group
involved in this theory is an affine extension of the tangent gauge group
acting on the tangent bundle of the space of connections. A mathematical
analysis of this group action and of the relevant BRST complex is discussed in
details.Comment: 74 pages, LaTeX, minor corrections; to be published in Commun. Math.
Phy
AKSZ-BV Formalism and Courant Algebroid-induced Topological Field Theories
We give a detailed exposition of the Alexandrov-Kontsevich-Schwarz-
Zaboronsky superfield formalism using the language of graded manifolds. As a
main illustarting example, to every Courant algebroid structure we associate
canonically a three-dimensional topological sigma-model. Using the AKSZ
formalism, we construct the Batalin-Vilkovisky master action for the model.Comment: 13 pages, based on lectures at Rencontres mathematiques de Glanon
200
The Relative Space: Space Measurements on a Rotating Platform
We introduce here the concept of relative space, an extended 3-space which is
recognized as the only space having an operational meaning in the study of the
space geometry of a rotating disk. Accordingly, we illustrate how space
measurements are performed in the relative space, and we show that an old-aged
puzzling problem, that is the Ehrenfest's paradox, is explained in this purely
relativistic context. Furthermore, we illustrate the kinematical origin of the
tangential dilation which is responsible for the solution of the Ehrenfest's
paradox.Comment: 14 pages, 2 EPS figures, LaTeX, to appear in the European Journal of
Physic
On the Observables Describing a Quantum Reference Frame
A reference frame F is described by the element g of the Poincare' group P
which connects F with a given fixed frame F_0. If F is a quantum frame, defined
by a physical object following the laws of quantum physics, the parameters of g
have to be considered as quantum observables. However, these observables are
not compatible and some of them, namely the coordinates of the origin of F,
cannot be represented by self-adjoint operators. Both these difficulties can be
overcome by considering a positive-operator-valued measure (POVM) on P,
covariant with respect to the left translations of the group, namely a
covariance system. We develop a construction procedure for this kind of
mathematical structure. The formalism is also used to discuss the quantum
observables measured with respect to a quantum reference frame.Comment: 23 pages, no figure
The Timing Counter of the MEG experiment: calibration and performance
The MEG detector is designed to test Lepton Flavor Violation in the
decay down to a Branching Ratio of a few
. The decay topology consists in the coincident emission of a
monochromatic photon in direction opposite to a monochromatic positron. A
precise measurement of the relative time is crucial to suppress
the background. The Timing Counter (TC) is designed to precisely measure the
time of arrival of the and to provide information to the trigger system.
It consists of two sectors up and down stream the decay target, each consisting
of two layers. The outer one made of scintillating bars and the inner one of
scintillating fibers. Their design criteria and performances are described.Comment: Presented at the 12th Topical Seminar on Innovative Particle and
Radiation Detectors (IPRD10) 7 - 10 June 2010, Siena. Accepted by Nuclear
Physics B (Proceedings Supplements) (2011)tal
Design and test of an extremely high resolution Timing Counter for the MEG II experiment: preliminary results
The design and tests of Timing Counter elements for the upgrade of the MEG
experiment, MEG II,is presented. The detector is based on several small plates
of scintillator with a Silicon PhotoMultipliers dual-side readout. The
optimisation of the single counter elements (SiPMs, scintillators, geometry) is
described. Moreover, the results obtained with a first prototype tested at the
Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati (LNF) are
presented.Comment: 10 pages, 7 figures. Presented at the 13th Topical Seminar on
Innovative Particle and Radiation Detectors (IPRD13) 7-10 October 2013 Siena,
Ital
Shear-Driven Dynamo Waves in the Fully Nonlinear Regime
Large-scale dynamo action is well understood when the magnetic Reynolds number (Rm) is small, but becomes problematic in the astrophysically relevant large Rm limit since the fluctuations may control the operation of the dynamo, obscuring the large-scale behavior. Recent works by Tobias & Cattaneo demonstrated numerically the existence of large-scale dynamo action in the form of dynamo waves driven by strongly helical turbulence and shear. Their calculations were carried out in the kinematic regime in which the back-reaction of the Lorentz force on the flow is neglected. Here, we have undertaken a systematic extension of their work to the fully nonlinear regime. Helical turbulence and large-scale shear are produced self-consistently by prescribing body forces that, in the kinematic regime, drive flows that resemble the original velocity used by Tobias & Cattaneo. We have found four different solution types in the nonlinear regime for various ratios of the fluctuating velocity to the shear and Reynolds numbers. Some of the solutions are in the form of propagating waves. Some solutions show large-scale helical magnetic structure. Both waves and structures are permanent only when the kinetic helicity is non-zero on average
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