2,469 research outputs found
The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean
The stable isotope composition of dissolved silicon in seawater (ÎŽ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40â60ââN) and Labrador Sea. Variations in ÎŽ30SiDSi below 500âm were closely tied to the distribution of water masses. Higher ÎŽ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower ÎŽ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest ÎŽ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the ÎŽ30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high ÎŽ30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both ÎŽ30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower Deep Water. The GEOVIDE ÎŽ30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local ÎŽ30SiDSi distribution
Neutrino Oscillations from Supersymmetry without R-parity - Its Implications on the Flavor Structure of the Theory
We discuss here some flavor structure aspects of the complete theory of
supersymmetry without R-parity addressed from the perspective of fitting
neutrino oscillation data based on the recent Super-Kamiokande result. The
single-VEV parametrization of supersymmetry without R-parity is first reviewed,
illustrating some important features not generally appreciated. For the flavor
structure discussions, a naive, flavor model independent, analysis is
presented, from which a few interesting things can be learned.Comment: 1+10 pages latex, no figure; Invited talk at NANP 99 conference,
Dubna (Jun 28 - Jul 3) --- submission for the proceeding
Toward Realistic Intersecting D-Brane Models
We provide a pedagogical introduction to a recently studied class of
phenomenologically interesting string models, known as Intersecting D-Brane
Models. The gauge fields of the Standard-Model are localized on D-branes
wrapping certain compact cycles on an underlying geometry, whose intersections
can give rise to chiral fermions. We address the basic issues and also provide
an overview of the recent activity in this field. This article is intended to
serve non-experts with explanations of the fundamental aspects, and also to
provide some orientation for both experts and non-experts in this active field
of string phenomenology.Comment: 85 pages, 8 figures, Latex, Bibtex, v2: refs added, typos correcte
Co-evolution of RDF Datasets
Linking Data initiatives have fostered the publication of large number of RDF
datasets in the Linked Open Data (LOD) cloud, as well as the development of
query processing infrastructures to access these data in a federated fashion.
However, different experimental studies have shown that availability of LOD
datasets cannot be always ensured, being RDF data replication required for
envisioning reliable federated query frameworks. Albeit enhancing data
availability, RDF data replication requires synchronization and conflict
resolution when replicas and source datasets are allowed to change data over
time, i.e., co-evolution management needs to be provided to ensure consistency.
In this paper, we tackle the problem of RDF data co-evolution and devise an
approach for conflict resolution during co-evolution of RDF datasets. Our
proposed approach is property-oriented and allows for exploiting semantics
about RDF properties during co-evolution management. The quality of our
approach is empirically evaluated in different scenarios on the DBpedia-live
dataset. Experimental results suggest that proposed proposed techniques have a
positive impact on the quality of data in source datasets and replicas.Comment: 18 pages, 4 figures, Accepted in ICWE, 201
Electric Dipole Moments in the Generic Supersymmetric Standard Model
The generic supersymmetric standard model is a model built from a
supersymmetrized standard model field spectrum the gauge symmetries only. The
popular minimal supersymmetric standard model differs from the generic version
in having R-parity imposed by hand. We review an efficient formulation of the
model and some of the recently obtained interesting phenomenological features,
focusing on one-loop contributions to fermion electric dipole moments.Comment: 1+7 pages Revtex 3 figures incoporated; talk at NANP'0
Instanton Induced Neutrino Majorana Masses in CFT Orientifolds with MSSM-like spectra
Recently it has been shown that string instanton effects may give rise to
neutrino Majorana masses in certain classes of semi-realistic string
compactifications. In this paper we make a systematic search for supersymmetric
MSSM-like Type II Gepner orientifold constructions admitting boundary states
associated with instantons giving rise to neutrino Majorana masses and other L-
and/or B-violating operators. We analyze the zero mode structure of D-brane
instantons on general type II orientifold compactifications, and show that only
instantons with O(1) symmetry can have just the two zero modes required to
contribute to the 4d superpotential. We however discuss how the addition of
fluxes and/or possible non-perturbative extensions of the orientifold
compactifications would allow also instantons with and U(1) symmetries
to generate such superpotentials. In the context of Gepner orientifolds with
MSSM-like spectra, we find no models with O(1) instantons with just the
required zero modes to generate a neutrino mass superpotential. On the other
hand we find a number of models in one particular orientifold of the Gepner
model with instantons with a few extra uncharged
non-chiral zero modes which could be easily lifted by the mentioned effects. A
few more orientifold examples are also found under less stringent constraints
on the zero modes. This class of instantons have the interesting
property that R-parity conservation is automatic and the flavour structure of
the neutrino Majorana mass matrices has a simple factorized form.Comment: 68 pages, 2 figures; v2. typos corrected, refs adde
Dynamical supersymmetry breaking with a large internal dimension
Supersymmetry breaking in string perturbation theory predicts the existence
of a new dimension at the TeV scale. The simplest realization of the minimal
supersymmetric Standard Model in the context of this mechanism has two
important consequences: (i) A natural solution to the -problem; (ii) The
absence of quadratic divergences in the cosmological constant, which leads to a
dynamical determination of the supersymmetry breaking and electroweak scale. We
present an explicit example in which the whole particle spectrum is given as a
function of the top quark mass. A generic prediction of this mechanism is the
existence of Kaluza-Klein excitations for gauge bosons and higgses. In
particular the first excitation of the photon could be accessible to future
accelerators and give a clear signal of the proposed mechanism.Comment: 27 pages, latex, 6 figures available by FAX upon reques
Instanton effects in N=1 brane models and the Kahler metric of twisted matter
We consider locally consistent systems of magnetized D9 branes on an
orbifolded six-torus which support N=1 gauge theories. In such realizations,
the matter multiplets arise from "twisted" strings connecting different stacks
of branes. The introduction of Euclidean 5 branes (E5) wrapped on the
six-dimensional compact space leads to instanton effects. For instance, if the
system is engineered so as to yield SQCD, a single E5 brane may account for the
ADS/TVY superpotential. We discuss the subtle interplay that exists between the
annuli diagrams with an E5 boundary and the holomorphicity properties of the
effective low-energy action of the N=1 theory. The consistency of this picture
allows to obtain information on the Kahler metric of the chiral matter
multiplets arising from twisted strings.Comment: 33 pages, 4 figures. V2: improved discussion, clarifyng comments and
references added. Version to be published in JHE
Gauging Away the Strong CP Problem
We propose a new solution to the strong-CP problem. It involves the existence
of an unbroken gauged symmetry whose gauge boson gets a Stuckelberg
mass term by combining with a pseudoscalar field . The latter has
axion-like couplings to so that the theta parameter may
be gauged away by a gauge transformation. This system leads to mixed
gauge anomalies and we argue that they are cancelled by the addition of an
appropriate Wess-Zumino term, so that no SM fermions need to be charged under
. We discuss scenarios in which the above set of fields and couplings
appear. The mechanism is quite generic, but a natural possibility is that the
the symmetry arises from bulk gauge bosons in theories with extra
dimensions or string models. We show that in certain D-brane Type-II string
models (with antisymmetric tensor field strength fluxes) higher dimensional
Chern-Simons couplings give rise to the required D=4 Wess-Zumino terms upon
compactification. In one of the possible string realizations of the mechanism
the gauge boson comes from the Kaluza-Klein reduction of the
eleven-dimensional metric in M-theory.Comment: 21 pages, latex, one eps figure; v2 improved discussio
Non-perturbative effective interactions from fluxes
Motivated by possible implications on the problem of moduli stabilization and
other phenomenological aspects, we study D-brane instanton effects in flux
compactifications. We focus on a local model and compute non-perturbative
interactions generated by gauge and stringy instantons in a N = 1 quiver theory
with gauge group U(N_0) x U(N_1) and matter in the bifundamentals. This model
is engineered with fractional D3-branes at a C^3/(Z_2 x Z_2) singularity, and
its non-perturbative sectors are described by introducing fractional
D-instantons. We find a rich variety of instanton-generated F- and D-term
interactions, ranging from superpotentials and Beasley-Witten like
multi-fermion terms to non-supersymmetric flux-induced instanton interactions.Comment: 37 pages, 7 figures. Final version published on JHEP. Section 4
modified in several points regarding string corrections in absence of fluxes;
in particular, section 4.3 is removed. Some other minor changes and two
references adde
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