52 research outputs found
ELKO Spinor Fields: Lagrangians for Gravity derived from Supergravity
Dual-helicity eigenspinors of the charge conjugation operator (ELKO spinor
fields) belong -- together with Majorana spinor fields -- to a wider class of
spinor fields, the so-called flagpole spinor fields, corresponding to the
class-(5), according to Lounesto spinor field classification based on the
relations and values taken by their associated bilinear covariants. There
exists only six such disjoint classes: the first three corresponding to Dirac
spinor fields, and the other three respectively corresponding to flagpole,
flag-dipole and Weyl spinor fields. Using the mapping from ELKO spinor fields
to the three classes Dirac spinor fields, it is shown that the
Einstein-Hilbert, the Einstein-Palatini, and the Holst actions can be derived
from the Quadratic Spinor Lagrangian (QSL), as the prime Lagrangian for
supergravity. The Holst action is related to the Ashtekar's quantum gravity
formulation. To each one of these classes, there corresponds a unique kind of
action for a covariant gravity theory. Furthermore we consider the necessary
and sufficient conditions to map Dirac spinor fields (DSFs) to ELKO, in order
to naturally extend the Standard Model to spinor fields possessing mass
dimension one. As ELKO is a prime candidate to describe dark matter and can be
obtained from the DSFs, via a mapping explicitly constructed that does not
preserve spinor field classes, we prove that in particular the
Einstein-Hilbert, Einstein-Palatini, and Holst actions can be derived from the
QSL, as a fundamental Lagrangian for supergravity, via ELKO spinor fields. The
geometric meaning of the mass dimension-transmuting operator - leading ELKO
Lagrangian into the Dirac Lagrangian - is also pointed out, together with its
relationship to the instanton Hopf fibration.Comment: 11 pages, RevTeX, accepted for publication in
Int.J.Geom.Meth.Mod.Phys. (2009
Effective Monopoles within Thick Branes
The monopole mass is revealed to be considerably modified in the thick
braneworld paradigm, and depends on the position of the monopole in the brane
as well. Accordingly, the monopole radius continuously increases, leading to an
unacceptable setting that can be circumvented when the brane thickness has an
upper limit. Despite such peculiar behavior, the quantum corrections accrued --
involving the classical monopole solution -- are shown to be still under
control. We analyze the monopole's peculiarities also taking into account the
localization of the gauge fields. Furthermore, some additional analysis in the
thick braneworld context and the similar behavior evinced by the topological
string are investigated.Comment: 7 pages, 1 figur
Two-photon final states in peripheral heavy ion collisions
We discuss processes leading to two photon final states in peripheral heavy
ion collisions at RHIC. Due to the large photon luminosity we show that the
continuum subprocess can be observed with a
large number of events. We study this reaction when it is intermediated by a
resonance made of quarks or gluons and discuss its interplay with the continuum
process, verifying that in several cases the resonant process ovewhelms the
continuum one. It is also investigated the possibility of observing a scalar
resonance (the meson) in this process. Assuming for the the
mass and total decay width values recently reported by the E791 Collaboration
we show that RHIC may detect this particle in its two photon decay mode if its
partial photonic decay width is of the order of the ones discussed in the
literature.Comment: 10 pages, 8 figure
Rigorous Formulation of Duality in Gravitational Theories
In this paper we evince a rigorous formulation of duality in gravitational
theories where an Einstein like equation is valid, by providing the conditions
under which the Hodge duals (with respect to the metric tensor g) of T^a and
R_b^a may be considered as the torsion and curvature 2-forms associated with a
connection D', part of a Riemann-Cartan structure (M,g',D'), in the cases g =
g' and g does not equal g', once T^a and R_b^a are the torsion and curvature
2-forms associated with a connection D part of a Riemann-Cartan structure
(M,g,D). A new form for the Einstein equation involving the dual of the Riemann
tensor of D is also provided, and the result is compared with others appearing
in the literature.Comment: 15 page
Testing the Resolving Power of 2-D K^+ K^+ Interferometry
Adopting a procedure previously proposed to quantitatively study
two-dimensional pion interferometry, an equivalent 2-D chi^2 analysis was
performed to test the resolving power of that method when applied to less
favorable conditions, i.e., if no significant contribution from long lived
resonances is expected, as in kaon interferometry. For that purpose, use is
made of the preliminary E859 K^+ K^+ interferometry data from Si+Au collisions
at 14.6 AGeV/c. As expected, less sensitivity is achieved in the present case,
although it still is possible to distinguish two distinct decoupling
geometries. The present analysis seems to favor scenarios with no resonance
formation at the AGS energy range, if the preliminary K^+ K^+ data are
confirmed. The possible compatibility of data with zero decoupling proper time
interval, conjectured by the 3-D experimental analysis, is also investigated
and is ruled out when considering more realistic dynamical models with
expanding sources. These results, however, clearly evidence the important
influence of the time emission interval on the source effective transverse
dimensions. Furthermore, they strongly emphasize that the static Gaussian
parameterization, commonly used to fit data, cannot be trusted under more
realistic conditions, leading to distorted or even wrong interpretation of the
source parameters!Comment: 11 pages, RevTeX, 4 Postscript figures include
Photon-Photon and Pomeron-Pomeron Processes in Peripheral Heavy Ion Collisions
We estimate the cross sections for the production of resonances, pion pairs
and a central cluster of hadrons in peripheral heavy-ion collisions through
two-photon and double-pomeron exchange, at energies that will be available at
RHIC and LHC. The effect of the impact parameter in the diffractive reactions
is introduced, and imposing the condition for realistic peripheral collisions
we verify that in the case of very heavy ions the pomeron-pomeron contribution
is indeed smaller than the electromagnetic one. However, they give a
non-negligible background in the collision of light ions. This diffractive
background will be more important at RHIC than at LHC.Comment: 22 pages, 1 Postscript figures, 4 tables, to appear in Phys. Rev.
Could the variation in quasar luminosity, due to extra dimension 3-brane in RS model, be measurable?
We propose an alternative theoretical approach showing how the existence of
an extra dimension in RS model can estimate the correction in the Schwarzschild
radius of black holes, and consequently its measurability in terms of the
variation of quasar luminosity, which can be caused by a imprint of an extra
dimension endowing the geometry of a brane-world scenario in an AdS_5 bulk.
This paper is intended to investigate the variation of luminosity due to
accretion of gas in black holes (BHs) in the center of quasars, besides also
investigating the variation of luminosity in supermassive BHs by brane-world
effects, using RS model.Comment: Revtex4, 7 Pages, 6 Figures, v2 has minor change
Success evaluation factors in construction project management : some evidence from medium and large portuguese companies
The construction industry plays a very important role in the Portuguese economy. In 2009, it was among the top five economic sectors, representing 13% of total employment. Nevertheless, project failures are still frequent mainly due to inadequate management practices and to the intrinsic characteristics of projects of the construction industry. Even though Portuguese construction has improved in recent years, cost and schedule overruns, low productivity and final product quality problems are still common. In this context, project management is a crucial tool for improving construction operations and for the overall success of projects. The aim of this article is to contribute to the discussion on success evaluation factors in a field where little has been written – the construction industry. Through a survey of 40 medium and large Portuguese companies several factors were identified which are currently considered in the evaluation of project success, as found in the literature review. The results show that the traditional factors, often referred to as the “Atkinson elements triangle” (cost, time and quality), are still the most relevant for evaluating the success of a project, but others, such as customer involvement and acceptance, have gained importance in recent years
Mechanical and Assembly Units of Viral Capsids Identified via Quasi-Rigid Domain Decomposition
Key steps in a viral life-cycle, such as self-assembly of a protective protein container or in some cases also subsequent maturation events, are governed by the interplay of physico-chemical mechanisms involving various spatial and temporal scales. These salient aspects of a viral life cycle are hence well described and rationalised from a mesoscopic perspective. Accordingly, various experimental and computational efforts have been directed towards identifying the fundamental building blocks that are instrumental for the mechanical response, or constitute the assembly units, of a few specific viral shells. Motivated by these earlier studies we introduce and apply a general and efficient computational scheme for identifying the stable domains of a given viral capsid. The method is based on elastic network models and quasi-rigid domain decomposition. It is first applied to a heterogeneous set of well-characterized viruses (CCMV, MS2, STNV, STMV) for which the known mechanical or assembly domains are correctly identified. The validated method is next applied to other viral particles such as L-A, Pariacoto and polyoma viruses, whose fundamental functional domains are still unknown or debated and for which we formulate verifiable predictions. The numerical code implementing the domain decomposition strategy is made freely available
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