803 research outputs found
Coronal mass ejections from the same active region cluster: Two different perspectives
The cluster formed by active regions (ARs) NOAA 11121 and 11123,
approximately located on the solar central meridian on 11 November 2010, is of
great scientific interest. This complex was the site of violent flux emergence
and the source of a series of Earth-directed events on the same day. The onset
of the events was nearly simultaneously observed by the Atmospheric Imaging
Assembly (AIA) telescope aboard the Solar Dynamics Observatory (SDO) and the
Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and
Heliospheric Investigation (SECCHI) suite of telescopes onboard the
Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The
progression of these events in the low corona was tracked by the Large Angle
Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO
imagers provided data from the Earth's perspective, whilst the STEREO twin
instruments procured images from the orthogonal directions. This spatial
configuration of spacecraft allowed optimum simultaneous observations of the AR
cluster and the coronal mass ejections that originated in it. Quadrature
coronal observations provided by STEREO revealed a notably large amount of
ejective events compared to those detected from Earth's perspective.
Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source
region indicate that all events classified by GOES as X-ray flares had an
ejective coronal counterpart in quadrature observations. These results have
direct impact on current space weather forecasting because of the probable
missing alarms when there is a lack of solar observations in a view direction
perpendicular to the Sun-Earth line.Comment: Solar Physics - Accepted for publication 2015-Apr-25 v2: Corrected
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Study of pinholes and nanotubes in AlInGaN films by cathodoluminescence and atomic force microscopy
Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) have been used to study the formation of pinholes in tensile and compressively strained AlInGaN films grown on Al2O3 substrates by plasma-induced molecular beam epitaxy. Nanotubes, pits, and V-shaped pinholes are observed in a tensile strained sample. CL images show an enhanced emission around the pits and a lower intensity at the V-shaped pinholes. Rounded pinholes appear in compressively strained samples in island-like regions with higher In concentration. The grain structure near the pinholes is resolved by AFM. (C) 2004 American Institute of Physics
Kahler Potentials of Chiral Matter Fields for Calabi-Yau String Compactifications
The Kahler potential is the least understood part of effective N=1
supersymmetric theories derived from string compactifications. Even at
tree-level, the Kahler potential for the physical matter fields, as a function
of the moduli fields, is unknown for generic Calabi-Yau compactifications and
has only been computed for simple toroidal orientifolds. In this paper we
describe how the modular dependence of matter metrics may be extracted in a
perturbative expansion in the Kahler moduli. Scaling arguments, locality and
knowledge of the structure of the physical Yukawa couplings are sufficient to
find the relevant Kahler potential. Using these techniques we compute the
`modular weights' for bifundamental matter on wrapped D7 branes for
large-volume IIB Calabi-Yau flux compactifications. We also apply our
techniques to the case of toroidal compactifications, obtaining results
consistent with those present in the literature. Our techniques do not provide
the complex structure moduli dependence of the Kahler potential, but are
sufficient to extract relevant information about the canonically normalised
matter fields and the soft supersymmetry breaking terms in gravity mediated
scenarios.Comment: JHEP style, 24 pages, 4 figures. v2: New section and reference adde
The twisted open string partition function and Yukawa couplings
We use the operator formalism to derive the bosonic contribution to the
twisted open string partition function in toroidal compactifications. This
amplitude describes, for instance, the planar interaction between g+1
magnetized or intersecting D-branes. We write the result both in the closed and
in the open string channel in terms of Prym differentials on the appropriate
Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing
the twisted partition function in the open string channel we obtain an explicit
expression for the 3-twist field correlator, which is the main ingredient in
the computation of Yukawa couplings in D-brane phenomenological models. This
provides an alternative method for computing these couplings that does not rely
on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte
Estimating the mass of CMEs from the analysis of EUV dimmings
Context. Reliable estimates of the mass of coronal mass ejections (CMEs) are required to quantify their energy and predict how they affect space weather. When a CME propagates near the observer's line of sight, these tasks involve considerable errors, which motivated us to develop alternative means for estimating the CME mass. Aims. We aim at further developing and testing a method that allows estimating the mass of CMEs that propagate approximately along the observer's line of sight. Methods. We analyzed the temporal evolution of the mass of 32 white-light CMEs propagating across heliocentric heights of 2.5-15 R, in combination with that of the mass evacuated from the associated low coronal dimming regions. The mass of the white-light CMEs was determined through existing methods, while the mass evacuated by each CME in the low corona was estimated using a recently developed technique that analyzes the dimming in extreme-UV (EUV) images. The combined white-light and EUV analyses allow the quantification of an empirical function that describes the evolution of CME mass with height. Results. The analysis of 32 events yielded reliable estimates of the masses of front-side CMEs. We quantified the success of the method by calculating the relative error with respect to the mass of CMEs determined from white-light STEREO data, where the CMEs propagate close to the plane of sky. The median for the relative error in absolute values is ≈30%; 75% of the events in our sample have an absolute relative error smaller than 51%. The sources of uncertainty include the lack of knowledge of piled-up material, subsequent additional mass supply from the dimming region, and limitations in the mass-loss estimation from EUV data. The proposed method does not rely on assumptions of CME size or distance to the observer's plane of sky and is solely based on the determination of the mass that is evacuated in the low corona. It therefore represents a valuable tool for estimating the mass of Earth-directed events.Fil: López, F. M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Cremades Fernandez, Maria Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Balmaceda, Laura Antonia. George Mason University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Nuevo, Federico Alberto. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Vásquez, A. M.. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad Nacional de Tres de Febrero; Argentin
Coisotropic D8-branes and Model-building
Up to now chiral type IIA vacua have been mostly based on intersecting
D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue
that there are additional BPS D-branes which have so far been neglected, and
which seem to have interesting model-building features. They are coisotropic
D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional
submanifolds of the CY which are trivial in homology, but contain a worldvolume
flux that induces D6-brane charge on them. This induced D6-brane charge not
only renders the D8-brane BPS, but also creates D=4 chirality when two
D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2
orientifold, where we provide explicit examples of coisotropic D8-branes. We
study the chiral spectrum, SUSY conditions, and effective field theory of
different systems of D8-branes in this orientifold, and show how the magnetic
fluxes generate a superpotential for untwisted Kahler moduli. Finally, using
both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like
type IIA vacua.Comment: 63 pages, 11 figures. Typos corrected and comments adde
One-loop Yukawas on Intersecting Branes
We calculate Yukawa interactions at one-loop on intersecting D6 branes. We
demonstrate the non-renormalization theorem in supersymmetric configurations,
and show how Yukawa beta functions may be extracted. In addition to the usual
logarithmic running, we find the power-law dependence on the infra-red cut-off
associated with Kaluza-Klein modes. Our results may also be used to evaluate
coupling renormalization in non-supersymmetric cases.Comment: 48 pages, 9 figures; minor corrections, JHEP styl
Orbifold resolutions with general profile
A very general class of resolved versions of the C/Z_N, T^2/Z_N and S^1/Z_2
orbifolds is considered and the free theory of 6D chiral fermions studied on
it. As the orbifold limit is taken, localized 4D chiral massless fermions are
seen to arise at the fixed points. Their number, location and chirality is
found to be independent on the detailed profile of the resolving space and to
agree with the result of hep-th/0409229, in which a particular resolution was
employed. As a consistency check of the resolution procedure, the massive
equation is numerically studied. In particular, for S^1/Z_2, the "resolved"
mass--spectrum and wave functions in the internal space are seen to correctly
reproduce the usual orbifold ones, as the orbifold limit is taken.Comment: 28 pages, 3 figures, typos corrected, references adde
Soft masses in superstring models with anomalous U(1) symmetries
We analyze the general structure of soft scalar masses emerging in
superstring models involving anomalous U(1) symmetries, with the aim of
characterizing more systematically the circumstances under which they can
happen to be flavor universal. We consider both heterotic orbifold and
intersecting brane models, possibly with several anomalous and non-anomalous
spontaneously broken U(1) symmetries. The hidden sector is assumed to consist
of the universal dilaton, Kahler class and complex structure moduli, which are
supposed to break supersymmetry, and a minimal set of Higgs fields which
compensate the Fayet-Iliopoulos terms. We leave the superpotential that is
supposed to stabilize the hidden sector fields unspecified, but we carefully
take into account the relations implied by gauge invariance and the constraints
required for the existence of a metastable vacuum with vanishing cosmological
constant. The results are parametrized in terms of a constrained Goldstino
direction, suitably defined effective modular weights, and the U(1) charges and
shifts. We show that the effect induced by vector multiplets strongly depends
on the functional form of the Kahler potential for the Higgs fields. We find in
particular that whenever these are charged matter fields, like in heterotic
models, the effect is non-trivial, whereas when they are shifting moduli
fields, like in certain intersecting brane models, the effect may vanish.Comment: 35 pages, LaTe
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