18,560 research outputs found
Higgs masses and Electroweak Precision Observables in the Lepton-Flavor-Violating MSSM
We study the effects of Lepton Flavor Violation (LFV) in the scalar lepton
sector of the MSSM on precision observables such as the W-boson mass and the
effective weak leptonic mixing angle, and on the Higgs-boson mass predictions.
The slepton mass matrices are parameterized in a model-independent way by a
complete set of dimensionless parameters which we constrain through LFV decay
processes and the precision observables. We find regions where both conditions
are similarly constraining. The necessary prerequisites for the calculation
have been added to FeynArts and FormCalc and are thus publicly available for
further studies. The obtained results are available in FeynHiggs.Comment: LaTeX, 30 page
The globular cluster system of NGC 1316 IV. Nature of the star cluster complex SH2
The light of the merger remnant NGC 1316 is dominated by old and
intermediate-age stars. The only sign of current star formation in this big
galaxy is the HII region SH2, an isolated star cluster complex with a ring-like
morphology and an estimated age of 0.1 Gyr at a galactocentric distance of
about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak
line emission and a few more young star clusters, is kinematically associated.
The origin of this complex is enigmatic. The nebular emission lines permit a
metallicity determination which can discriminate between a dwarf galaxy or
other possible precursors. We used the Integrated Field Unit of the VIMOS
instrument at the Very Large Telescope of the European Southern Observatory to
study the morphology, kinematics, and metallicity employing line maps, velocity
maps, and line diagnostics of a few characteristic spectra. The line ratios of
different spectra vary, indicating highly structured HII regions, but define a
locus of uniform metallicity. The strong-line diagnostic diagrams and empirical
calibrations point to a nearly solar or even super-solar oxygen abundance. The
velocity dispersion of the gas is highest in the region offset from the bright
clusters. Star formation may be active on a low level. There is evidence for a
large-scale disk-like structure in the region of SH2, which would make the
similar radial velocity of the nearby globular cluster easier to understand.
The high metallicity does not fit to a dwarf galaxy as progenitor. We favour
the scenario of a free-floating gaseous complex having its origin in the merger
2 Gyr ago. Over a long period the densities increased secularly until finally
the threshold for star formation was reached. SH2 illustrates how massive star
clusters can form outside starbursts and without a considerable field
population.Comment: 10 pages, 5 figures, accepted for Astronomy & Astrophysic
Gravitational waveforms with controlled accuracy
A partially first-order form of the characteristic formulation is introduced
to control the accuracy in the computation of gravitational waveforms produced
by highly distorted single black hole spacetimes. Our approach is to reduce the
system of equations to first-order differential form on the angular
derivatives, while retaining the proven radial and time integration schemes of
the standard characteristic formulation. This results in significantly improved
accuracy over the standard mixed-order approach in the extremely nonlinear
post-merger regime of binary black hole collisions.Comment: Revised version, published in Phys. Rev. D, RevTeX, 16 pages, 4
figure
Aspects of open-flavour mesons in a comprehensive DSBSE study
Open-flavour meson studies are the necessary completion to any comprehensive
investigation of quarkonia. We extend recent studies of quarkonia in the
Dyson-Schwinger-Bethe-Salpeter-equation approach to explore their results for
all possible flavour combinations. Within the inherent limitations of the
setup, we present the most comprehensive results for meson masses and leptonic
decay constants currently available and put them in perspective with respect to
experiment and other approaches.Comment: 38 pages, 26 figures, 2 tables, revised according to reviewer
comment
The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796
The isolated elliptical (IE) NGC 7796 is accompanied by an interesting
early-type dwarf galaxy, named NGC7796-DW1. It exhibits a tidal tail, very boxy
isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the
bulk population of the galaxy, indicating a younger age. These properties are
suggestive of a dwarf-dwarf merger remnant. We use the Multi-Unit Spectroscopic
Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract
characteristic spectra to which we apply the STARLIGHT population synthesis
software to obtain ages and metallicities of the various population components
of the galaxy. The galaxy's main body is old and metal-poor. A surprising
result is the extended line emission in the galaxy, forming a ring-like
structure with a projected diameter of 2.2 kpc. The line ratios fall into the
regime of HII-regions, although OB-stellar populations cannot be identified by
spectral signatures. Nucleus A is a relatively old (7 Gyr or older) and
metal-poor super star cluster, most probably the nucleus of the dwarf, now
displaced. The star-forming regions B and C show younger and distinctly more
metal-rich components. The emission line ratios of regions B and C indicate an
almost solar oxygen abundance, if compared with radiation models of HII
regions. NGC7796-DW1 occupies a particular role in the group of transition-type
galaxies with respect to its origin and current evolutionary state, being the
companion of an IE. The dwarf-dwarf merger scenario is excluded because of the
missing metal-rich merger component. A viable alternative is gas accretion from
a reservoir of cold, metal-rich gas. NGC7796 has to provide this gas within its
X-ray bright halo. As illustrated by NGC7796-DW1, cold accretion may be a
general solution to the problem of extended star formation histories in
transition dwarf galaxies. (abridged)Comment: comments: 13 pages, 8 figures, accepted for publication in Astronomy
& Astrophysic
Kinematic groups across the MW disc: insights from models and from the RAVE catalogue
With the advent of the Gaia data, the unprecedented kinematic census of great
part of the Milky Way disc will allow us to characterise the local kinematic
groups and new groups in different disc neighbourhoods. First, we show here
that the models predict a stellar kinematic response to the spiral arms and bar
strongly dependent on disc position. For example, we find that the kinematic
groups induced by the spiral arm models change significantly if one moves only
~ 0.6 kpc in galactocentric radius, but ~ 2 kpc in azimuth. There are more and
stronger groups as one approaches the spiral arms. Depending on the spiral
pattern speed, the kinematic imprints are more intense in nearby vicinities or
far from the Sun. Secondly, we present a preliminary study of the kinematic
groups observed by RAVE. This sample will allow us, for the first time, to
study the dependence on Galactic position of the (thin and thick) disc moving
groups. In the solar neighbourhood, we find the same kinematics groups as
detected in previous surveys, but now with better statistics and over a larger
spatial volume around the Sun. This indicates that these structures are indeed
large scale kinematic features.Comment: 4 pages, 3 figures, to appear in the proceedings of "Assembling the
Puzzle of the Milky Way", Le Grand Bornand (April 17-22, 2011), C. Reyle, A.
Robin, M. Schultheis (eds.
Understanding the spiral structure of the Milky Way using the local kinematic groups
We study the spiral arm influence on the solar neighbourhood stellar
kinematics. As the nature of the Milky Way (MW) spiral arms is not completely
determined, we study two models: the Tight-Winding Approximation (TWA) model,
which represents a local approximation, and a model with self-consistent
material arms named PERLAS. This is a mass distribution with more abrupt
gravitational forces. We perform test particle simulations after tuning the two
models to the observational range for the MW spiral arm properties. We explore
the effects of the arm properties and find that a significant region of the
allowed parameter space favours the appearance of kinematic groups. The
velocity distribution is mostly sensitive to the relative spiral arm phase and
pattern speed. In all cases the arms induce strong kinematic imprints for
pattern speeds around 17 km/s/kpc (close to the 4:1 inner resonance) but no
substructure is induced close to corotation. The groups change significantly if
one moves only ~0.6 kpc in galactocentric radius, but ~2 kpc in azimuth. The
appearance time of each group is different, ranging from 0 to more than 1 Gyr.
Recent spiral arms can produce strong kinematic structures. The stellar
response to the two potential models is significantly different near the Sun,
both in density and kinematics. The PERLAS model triggers more substructure for
a larger range of pattern speed values. The kinematic groups can be used to
reduce the current uncertainty about the MW spiral structure and to test
whether this follows the TWA. However, groups such as the observed ones in the
solar vicinity can be reproduced by different parameter combinations. Data from
velocity distributions at larger distances are needed for a definitive
constraint.Comment: 18 pages, 21 figures, 4 tables; acccepted for publication in MNRA
Gravitational Waves from a Fissioning White Hole
We present a fully nonlinear calculation of the waveform of the gravitational
radiation emitted in the fission of a vacuum white hole. At early times, the
waveforms agree with close-approximation perturbative calculations but they
reveal dramatic time and angular dependence in the nonlinear regime. The
results pave the way for a subsequent computation of the radiation emitted
after a binary black hole merger.Comment: 11 pages, 6 figures, RevTeX
Relación entre estado de conocimiento en fracciones y problemas descriptivos de fracciones
Este trabajo forma parte de un estudio que pretende examinar la relación entre las habilidades en fracciones de los escolares y su desempeño en la resolución de los problemas descriptivos de fracciones. Para ello se realiza un análisis descriptivo e inferencial de los datos obtenidos en una muestra de 85 estudiantes de 2º de Grado en Magisterio de la U. de Valencia a los que se les ha aplicado un test inicial de conocimiento genérico de las habilidades con fracciones y se les ha planteado un tipo específico de problemas descriptivos de fracciones, el de fracciones encadenadas por el complemento aritmético
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