828 research outputs found
Atomic Parity-Violation and Precision Physics
The atomic parity-violation (APV) parameter QW for a nucleus with `n'
neutrons and `z' protons has been included in the list of pseudo-observables
accessible with the codes TOPAZ0 and ZFITTER. In this way one can add the APV
results in the LEP EWWG `global' electroweak fits, checking the corresponding
effect when added to the existing precision measurements.Comment: 9 Late
From Peierls brackets to a generalized Moyal bracket for type-I gauge theories
In the space-of-histories approach to gauge fields and their quantization,
the Maxwell, Yang--Mills and gravitational field are well known to share the
property of being type-I theories, i.e. Lie brackets of the vector fields which
leave the action functional invariant are linear combinations of such vector
fields, with coefficients of linear combination given by structure constants.
The corresponding gauge-field operator in the functional integral for the
in-out amplitude is an invertible second-order differential operator. For such
an operator, we consider advanced and retarded Green functions giving rise to a
Peierls bracket among group-invariant functionals. Our Peierls bracket is a
Poisson bracket on the space of all group-invariant functionals in two cases
only: either the gauge-fixing is arbitrary but the gauge fields lie on the
dynamical sub-space; or the gauge-fixing is a linear functional of gauge
fields, which are generic points of the space of histories. In both cases, the
resulting Peierls bracket is proved to be gauge-invariant by exploiting the
manifestly covariant formalism. Moreover, on quantization, a gauge-invariant
Moyal bracket is defined that reduces to i hbar times the Peierls bracket to
lowest order in hbar.Comment: 14 pages, Late
Non-Local Boundary Conditions in Euclidean Quantum Gravity
Non-local boundary conditions for Euclidean quantum gravity are proposed,
consisting of an integro-differential boundary operator acting on metric
perturbations. In this case, the operator P on metric perturbations is of
Laplace type, subject to non-local boundary conditions; by contrast, its
adjoint is the sum of a Laplacian and of a singular Green operator, subject to
local boundary conditions. Self-adjointness of the boundary-value problem is
correctly formulated by looking at Dirichlet-type and Neumann-type realizations
of the operator P, following recent results in the literature. The set of
non-local boundary conditions for perturbative modes of the gravitational field
is written in general form on the Euclidean four-ball. For a particular choice
of the non-local boundary operator, explicit formulae for the boundary-value
problem are obtained in terms of a finite number of unknown functions, but
subject to some consistency conditions. Among the related issues, the problem
arises of whether non-local symmetries exist in Euclidean quantum gravity.Comment: 23 pages, plain Tex. The revised version is much longer, and new
original calculations are presented in section
Methyltrioxorhenium catalysed synthesis of highly oxidised aryltetralin lignans with anti-topoisomerase II and apoptogenic activities
A novel and efficient procedure to prepare highly oxidised aryltetralin lignans, such as isopodophyllotoxone and (-)-aristologone
derivatives, by oxidation of podophyllotoxin and galbulin with methylrhenium trioxide (MTO) and novel MTO heterogeneous
catalysts is reported. It is noteworthy that in the case of isopodophyllotoxone derivatives the functionalisation of the
C-4 position of the C-ring and the ring-opening of the D-lactone moiety increased the activity against topoisomerase II while causing
the undesired inhibition of tubulin polymerisation to disappear. The novel (-)-aristologone derivatives showed apoptogenic
activity against resistant human lymphoma cell lines.L'articolo è disponibile sul sito dell'editore: http://www.sciencedirect.co
Non-commutative Kerr black hole
This paper applies the first-order Seiberg-Witten map to evaluate the
first-order non-commutative Kerr tetrad. The classical tetrad is taken to
follow the locally non-rotating frame prescription. We also evaluate the tiny
effect of non-commutativity on the efficiency of the Penrose process of
rotational energy extraction from a black hole.Comment: 14 pages. The original calculations are completely ne
Performance Assessment of a Solar Assisted Ground Source Heat Pump in a Mountain Site
Abstract Systems based on the integrated use of multiple renewable energy sources, such as “Solar Assisted Geothermal Heat Pumps” (SAGHPs), seem to increase efficiency and overcome limits of the use of traditional heat pump systems. In this work, a \SAGHP\ providing energy for heating and \DHW\ of a newly built restaurant in an Alpine ski park was analyzed through transient simulations with TRNSYS®, following the collection of information about the system component, the operation and the weather conditions of the mountain site. The annual energy balance allowed different system operation modes to be compared
Self-Dual Action for Fermionic Fields and Gravitation
This paper studies the self-dual Einstein-Dirac theory. A generalization is
obtained of the Jacobson-Smolin proof of the equivalence between the self-dual
and Palatini purely gravitational actions. Hence one proves equivalence of
self-dual Einstein-Dirac theory to the Einstein-Cartan-Sciama-Kibble-Dirac
theory. The Bianchi symmetry of the curvature, core of the proof, now contains
a non-vanishing torsion. Thus, in the self-dual framework, the extra terms
entering the equations of motion with respect to the standard Einstein-Dirac
field equations, are neatly associated with torsion.Comment: 13 pages, plain-tex, recently appearing in Nuovo Cimento B, volume
109, pages 973-982, September 199
Essential self-adjointness in one-loop quantum cosmology
The quantization of closed cosmologies makes it necessary to study squared
Dirac operators on closed intervals and the corresponding quantum amplitudes.
This paper proves self-adjointness of these second-order elliptic operators.Comment: 14 pages, plain Tex. An Erratum has been added to the end, which
corrects section
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