591 research outputs found
Tensor hierarchies, Borcherds algebras and E11
Gauge deformations of maximal supergravity in D=11-n dimensions generically
give rise to a tensor hierarchy of p-form fields that transform in specific
representations of the global symmetry group E(n). We derive the formulas
defining the hierarchy from a Borcherds superalgebra corresponding to E(n).
This explains why the E(n) representations in the tensor hierarchies also
appear in the level decomposition of the Borcherds superalgebra. We show that
the indefinite Kac-Moody algebra E(11) can be used equivalently to determine
these representations, up to p=D, and for arbitrarily large p if E(11) is
replaced by E(r) with sufficiently large rank r.Comment: 22 pages. v2: Published version (except for a few minor typos
detected after the proofreading, which are now corrected
Non-geometric fluxes and mixed-symmetry potentials
We discuss the relation between generalised fluxes and mixed-symmetry
potentials. We first consider the NS fluxes, and point out that the
`non-geometric' flux is dual to a mixed-symmetry potential with a set of
nine antisymmetric indices. We then consider the T-duality family of fluxes
whose prototype is the Scherk-Schwarz reduction of the S-dual of the RR scalar
of IIB supergravity. Using the relation with mixed-symmetry potentials, we are
able to give a complete classification of these fluxes, including the ones that
are non-geometric. The non-geometric fluxes again turn out to be dual to
potentials containing nine antisymmetric indices. Our analysis suggests that
all these fluxes can be understood in the context of double field theory,
although for the non-geometric ones one expects a violation of the strong
constraint.Comment: 19 pages, refs. adde
Duality Symmetries and G^{+++} Theories
We show that the non-linear realisations of all the very extended algebras
G^{+++}, except the B and C series which we do not consider, contain fields
corresponding to all possible duality symmetries of the on-shell degrees of
freedom of these theories. This result also holds for G_2^{+++} and we argue
that the non-linear realisation of this algebra accounts precisely for the form
fields present in the corresponding supersymmetric theory. We also find a
simple necessary condition for the roots to belong to a G^{+++} algebra.Comment: 35 pages. v2: 2 appendices added, other minor corrections. v3: tables
corrected, other minor changes, one appendix added, refs. added. Version
published in Class. Quant. Gra
Recording Risk Factors of Physical Abuse in Children Younger Than 36 Months With Bone Fractures: A 12-Years Retrospective Study in an Italian General Hospital Emergency Room
Skeletal fractures (SFs) are very common in pediatrics. In some cases, they are secondary to child abuse. Differentiation of accidental from non-accidental fractures (NAFs) is essential as in abused children risk of further injuries leading to severe clinical problems and death is significant. Main objectives of this study were to evaluate the characteristics of SFs of children ≤3 years of age presenting to the Emergency Room (ER) of a Children's Teaching Hospital over a 12-year period and the attention paid by ER physicians to the identification of the indicators that increase suspicion of NAF and that suggest referring of the patient to the child protection agencies. This is a descriptive, retrospective study of the medical records of all the pediatric patients ≤ 36 months of age admitted to the ER of the Azienda Ospedaliera Santa Maria della Misericordia, University of Perugia, Perugia, Italy, for radiological documented SFs between January 1, 2004, and March 31, 2016. Available information was used to evaluate whether indicators of possible child abuse were documented by the ER staff and whether diagnosis of potential abuse was followed by further screening or referral to child protection agencies. During the study period, 11,136 accesses of the ER by children younger than 36 months were documented, among whom 417 presented long bone or skull fractures. Skull fractures were significantly more common among children <12 months of age (p = 0.001), whereas radius/ulna and humerus fractures were diagnosed significantly more frequently in children 12–36 months of age (p = 0.036 and p = 0.022, respectively). Recorded medical history was considered inadequate in 255 (61.2%) cases with no difference related to patient's age. Our study showed that the majority of charts in case of SFs were found to contain inadequate documentation to explain causes at the heart of the fractures and, therefore, to rule out any inflicted trauma. The development of specific referral guidelines, along with the continuous education and training of health professionals, as well as the preparation of structured medical forms, are essential measures to activate in order to improve the referral of children from the ER to child protection agencies
Spectrum of D=6, N=4b Supergravity on AdS_3 x S^3
The complete spectrum of D=6, N=4b supergravity with n tensor multiplets
compactified on AdS_3 x S^3 is determined. The D=6 theory obtained from the K_3
compactification of Type IIB string requires that n=21, but we let n be
arbitrary. The superalgebra that underlies the symmetry of the resulting
supergravity theory in AdS_3 coupled to matter is SU(1,1|2)_L x SU(1,1|2)_R.
The theory also has an unbroken global SO(4)_R x SO(n) symmetry inherited from
D=6. The spectrum of states arranges itself into a tower of spin-2
supermultiplets, a tower of spin-1, SO(n) singlet supermultiplets, a tower of
spin-1 supermultiplets in the vector representation of SO(n) and a special
spin-1/2 supermultiplet also in the vector representation of SO(n). The SU(2)_L
x SU(2)_R Yang-Mills states reside in the second level of the spin-2 tower and
the lowest level of the spin-1, SO(n) singlet tower and the associated field
theory exhibits interesting properties.Comment: 37 pages, latex, 5 tables and 3 figures, typos corrected, a reference
adde
Non-propagating degrees of freedom in supergravity and very extended G_2
Recently a correspondence between non-propagating degrees of freedom in
maximal supergravity and the very extended algebra E_11 has been found. We
perform a similar analysis for a supergravity theory with eight supercharges
and very extended G_2. In particular, in the context of d=5 minimal
supergravity, we study whether supersymmetry can be realised on higher-rank
tensors with no propagating degrees of freedom. We find that in this case the
very extended algebra fails to capture these possibilities.Comment: 12 pages, 1 figure. v2: transformation properties of higher-rank
tensors under SU(2) R-symmetry analysed and refs added. v3: improved
discussion, published versio
Singular supersymmetric sigma models
Supersymmetric non-linear sigma-models are described by a field dependent
Kaehler metric determining the kinetic terms. In general it is not guaranteed
that this metric is always invertible. Our aim is to investigate the symmetry
structure of supersymmetric models in four dimensional space-time in which
metric singularities occur. For this purpose we study a simple anomaly-free
extension of the supersymmetric CP^1 model from a classical point of view. We
show that the metric singularities can be regularized by the addition of a soft
supersymmetry-breaking mass parameter.Comment: 21 pages, no figure
Provenance support for service-based infrastructure
Service-based architectures represent the next evolutionary step in the development of e-science, namely, the transformation of the Internet from a commercial marketplace to a mechanism for sharing multidisciplinary scientific resources. Although scientists in many disciplines have become increasingly reliant on distributed computing technologies for data processing and dissemination, the record of the processing history and origin of a data product, that is its data provenance, is often nonexistent, incomplete or impossible to recover by potential users. This thesis aims to address data provenance issues in service-based environments, particularly to answer how a scientist who performs a workflow execution in such an environment can (1) document the data provenance for a data item created by the execution, and (2) use the provenance documentation as a recipe to re-execute the workflow. This thesis pro poses a provenance model for delivering data provenance support in a service-based environment. Through the use of an example scenario of a scientific workflow in the Astrophysics domain, we explore and identify components of the provenance model. The provenance model proposes a technique to collect and record data provenance for service-based workflow executions. The technique facilitates the collection of data provenance of workflow execution at runtime. In order to record the collected data provenance, the thesis also proposes a specification to represent provenance to de scribe the processing history whereby a piece of data was derived. The thesis also proposes query interfaces that allow recorded provenance to be queried, has formulated a technique to construct provenance graphs, and supports the re-execution of past workflows. The provenance representation specification, the collection technique, and the query interfaces have been used to implement a prototype system to demonstrate the proposed model. The thesis also experimentally evaluates the scalability of the components implemented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Gauge fields and infinite chains of dualities
We show that the particle states of Maxwell's theory, in dimensions, can
be represented in an infinite number of ways by using different gauge fields.
Using this result we formulate the dynamics in terms of an infinite set of
duality relations which are first order in space-time derivatives. We derive a
similar result for the three form in eleven dimensions where such a possibility
was first observed in the context of E11. We also give an action formulation
for some of the gauge fields. In this paper we give a pedagogical account of
the Lorentz and gauge covariant formulation of the irreducible representations
of the Poincar\'e group, used previously in higher spin theories, as this plays
a key role in our constructions. It is clear that our results can be
generalised to any particle.Comment: 37 page
E11, generalised space-time and equations of motion in four dimensions
We construct the non-linear realisation of the semi-direct product of E11 and
its first fundamental representation at low levels in four dimensions. We
include the fields for gravity, the scalars and the gauge fields as well as the
duals of these fields. The generalised space-time, upon which the fields
depend, consists of the usual coordinates of four dimensional space-time and
Lorentz scalar coordinates which belong to the 56-dimensional representation of
E7. We demand that the equations of motion are first order in derivatives of
the generalised space-time and then show that they are essentially uniquely
determined by the properties of the E11 Kac-Moody algebra and its first
fundamental representation. The two lowest equations correctly describe the
equations of motion of the scalars and the gauge fields once one takes the
fields to depend only on the usual four dimensional space-time
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