1,041 research outputs found
On the Stability of Randall-Sundrum Braneworlds with Conformal Bulk Fields
In the Randall-Sundrum scenario we consider exact 5-dimensional solutions
with localized gravity which are associated with a well defined class of
conformal bulk fields. We analyze their behaviour under radion field
perturbations. We show that if the Randall-Sundrum exponential warp is the
localizing metric function and the equation of state of the conformal fields is
not changed by the radion perturbation then the 5-dimensional solutions are
unstable. We present new stable solutions which describe on the brane the
dynamics of inhomogeneous dust, generalized dark radiation and homogeneous
polytopic matter.Comment: 10 pages, latex, no figures. Contribution to the special issue of
Vestnik of Tomsk State Pedagogical University in the field
QFT/Cosmology/Gravity/Strings, edited by Sergei D. Odintso
Braneworlds, Conformal Fields and Dark Energy
In the Randall-Sundrum scenario we analize the dynamics of a spherically
symmetric 3-brane when matter fields propagate in the bulk. For a well defined
class of conformal fields of weight -4 we determine a new set of exact
5-dimensional solutions which localize gravity in the vicinity of the brane and
are stable under radion field perturbations. Geometries which describe the
dynamics of inhomogeneous dust, generalized dark radiation and homogeneous
polytropic dark energy are shown to belong to this set.Comment: 7 pages, latex, no figures. Talk given at the Fifth International
Workshop on New Worlds in Astroparticle Physics, University of Algarve, Faro,
8-10 January 2005. To be published in the workshop proceeding
Inhomogeneous Dark Radiation Dynamics on a de Sitter Brane
Assuming spherical symmetry we analyse the dynamics of an inhomogeneous dark
radiation vaccum on a Randall and Sundrum 3-brane world. Under certain natural
conditions we show that the effective Einstein equations on the brane form a
closed system. On a de Sitter brane and for negative dark energy density we
determine exact dynamical and inhomogeneous solutions which depend on the brane
cosmological constant, on the dark radiation tidal charge and on its initial
configuration. We also identify the conditions leading to the formation of a
singularity or of regular bounces inside the dark radiation vaccum.Comment: 6 pages, LaTeX, 1 EPS figure. Talk given at the Workshop The
Cosmology of Extra Dimensions and Varying Fundamental Constants of the
Conference JENAM 2002, The Unsolved Universe: Challenges for the Future, 2-7
September 2002, Porto, Portuga
Implications of anomalous gauge boson interactions to the fermion electromagnetic moments
We calculate the electromagnetic fermion form-factors induced by the
anomalous gauge boson interactions contained in the operators ODW and ODB.
Other results regarding anomalous triple gauge boson interactions are briefly
overviewed. We study the interplay between vertex corrections and gauge boson
self-energies extended to the longitudinal degrees of freedom. The physical
couplings to an external electromagnetic field are then derived.Comment: 14 pages, LATeX, to appear in Modern Physics Letters A, some literary
changes, a few notation correction
Dark Radiation and Localization of Gravity on the Brane
We discuss the dynamics of a spherically symmetric dark radiation vaccum in
the Randall-Sundrum brane world scenario. Under certain natural assumptions we
show that the Einstein equations on the brane form a closed system. For a de
Sitter brane we determine exact dynamical and inhomogeneous solutions which
depend on the brane cosmological constant, on the dark radiation tidal charge
and on its initial configuration. We define the conditions leading to singular
or globally regular solutions. We also analyse the localization of gravity near
the brane and show that a phase transition to a regime where gravity propagates
away from the brane may occur at short distances during the collapse of
positive dark energy density.Comment: 7 pages, latex with 2 eps figures. Talk given by Rui Neves, Fourth
International Workshop on New Worlds in Astroparticle Physics, Algarve
University, Faro, 5-7 September, 2002. To be published in the corresponding
proceedings, World Scientifi
Polchinski ERG equation and 2D scalar field theory
We investigate a -symmetric scalar field theory in two dimensions using
the Polchinski exact renormalization group equation expanded to second order in
the derivative expansion. We find preliminary evidence that the Polchinski
equation is able to describe the non-perturbative infinite set of fixed points
in the theory space, corresponding to the minimal unitary series of 2D
conformal field theories. We compute the anomalous scaling dimension and
the correlation length critical exponent showing that an accurate fit to
conformal field theory selects particular regulating functions.Comment: 9 pages, latex with 2 figures, uses sprocl.sty. To be published in
the Proceedings of the Workshop on the Exact Renormalization Group held in
Faro, Portugal, in September 10-12 1998, World Scientifi
Polchinski ERG Equation in O(N) Scalar Field Theory
We investigate the Polchinski ERG equation for d-dimensional O(N) scalar
field theory. In the context of the non-perturbative derivative expansion we
find families of regular solutions and establish their relation with the
physical fixed points of the theory. Special emphasis is given to the large N
limit for which many properties can be studied analytically.Comment: 7 pages, 4 figures, uses latex sprocl style. Two references added. To
be published in the proceedings of the Second Conference on the Exact
Renormalization Group (Rome, September 18-22, 2000), World Scientifi
Da lógica do mosaico à lógica do projecto: as actividades de enriquecimento curricular na escola do 1º CEB
Resumo indisponÃvel
Braneworlds, Conformal Fields and the Gravitons
We investigate the dynamics of Randall-Sundrum AdS5 braneworlds with
5-dimensional conformal matter fields. In the scenario with a compact fifth
dimension the class of conformal fields with weight -4 is associated with exact
5-dimensional warped geometries which are stable under radion field
perturbations and describe on the brane the dynamics of inhomogeneous dust,
generalized dark radiation and homogeneous polytropic dark energy. We analyse
the graviton mode flutuations around this class of background solutions and
determine their mass eigenvalues and wavefunctions from a Sturm-Liouville
problem. We show that the localization of gravity is not sharp enough for large
mass hierarchies to be generated. We also discuss the physical bounds imposed
by experiments in particle physics, in astrophysics and in precise measurements
of the low energy gravitational interaction.Comment: LaTeX, 9 pages, 2 figures. Based on talk given in the Second
International Conference on Quantum Theories and the Renormalization Group in
Gravity and Cosmology, CSIC and University of Barcelona, Barcelona, Spain,
11-15 July 2006. Submitted to be published in the Conference Proceedings, J.
Phys. A: Math. Ge
Actividades de enriquecimento curricular no 1º Ciclo do Ensino Básico: um olhar sobre a avaliação
Este texto centrado sobre as Actividades de Enriquecimento Curricular (AEC) na escola do 1º Ciclo do Ensino Básico (CEB) pretende reflectir sobre os desafios da avaliação nesta componente educativa em generalização neste nÃvel de ensino.
Para isso, são previamente enquadradas questões conceptuais das AEC no actual contexto da realidade das escolas e equacionadas a natureza, o papel e
caracterÃsticas da sua avaliação contextualizada. Tendo como ponto de partida
o enquadramento legislativo das AEC, são utilizados dados identificados em vários
relatórios nacionais e internacionais, bem como relatos de realidades locais que
ilustram as suas práticas educativas. Decorrente destas reflexões, são enunciados
princÃpios e propostas de equacionar e operacionalizar a avaliação nas e das AEC
na escola do 1º CEB.The present text, focussing on Curricular Enrichment Activities (CEA) in primary
education, aims at reflecting about the assessment challenges of this educational
component that is under generalisation in this level of teaching. For that purpose
we first discuss the conceptual issues of CEA within the present context of the reality
of schools and equate the nature, role and characteristics of their contextualised
assessment. Taking the legislative background of CEA as a starting point we will use data identified in various national and international reports as well as local reality
testimonies that illustrate CEA educational practices. From these reflections we offer
principles and proposals with a view to equating and performing assessment in and
of CEA in primary education schools.Cet article a pour but de réfléchir sur l’évaluation des Activités Extra-Curriculaires
(AEC) dans le cadre de l’enseignement primaire. On analyse, du point de
vue théorique, le rôle joué par les AEC dans ce niveau d’enseignement,
ainsi que la nature et les caractéristiques spécifiques de son évaluation
dans ce contexte. Les données analysées sont issues de rapports nationaux
et internationaux (ayant pour base les lois qui soutiennent les AEC) et des
rapports locaux traitant plus directement de pratiques éducatives courantes.
L’analyse débouche sur un ensemble de recommandations concernant les
pratiques et l’évaluation attachées aux AEC dans les écoles primaires portugaises
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