1,688 research outputs found
Realization of Minimal Supergravity
Minimal supergravity mediation of supersymmetry breaking has attracted much
attention due to its simplicity, which leads to its predictive power. We
consider how Nature possibly realizes minimal supergravity through inflationary
selection of the theory. Minimality is impressively consistent with the present
observational bounds and it might be tested with the aid of low-energy soft
parameters obtained in future experiments.Comment: 18 pages, 5 figure
Spectral properties and geology of bright and dark material on dwarf planet Ceres
Variations and spatial distributions of bright and dark material on dwarf
planet Ceres play a key role in understanding the processes that have led to
its present surface composition. We define limits for bright and dark material
in order to distinguish them consistently, based on the reflectance of the
average surface using Dawn Framing Camera data. A systematic classification of
four types of bright material is presented based on their spectral properties,
composition, spatial distribution, and association with specific
geomorphological features. We found obvious correlations of reflectance with
spectral shape (slopes) and age; however, this is not unique throughout the
bright spots. Although impact features show generally more extreme reflectance
variations, several areas can only be understood in terms of inhomogeneous
distribution of composition as inferred from Dawn Visible and Infrared
Spectrometer data. Additional material with anomalous composition and spectral
properties are rare. The identification of the composition and origin of the
dark, particularly the darkest material, remains to be explored. The spectral
properties and the morphology of the dark sites suggest an endogenic origin,
but it is not clear whether they are more or less primitive surficial exposures
or excavated subsurface but localized material. The reflectance, spectral
properties, inferred composition, and geologic context collectively suggest
that the bright and dark material tends to gradually change toward the average
surface over time. This could be because of multiple processes, i.e., impact
gardening/space weathering, and lateral mixing, including thermal and aqueous
alteration, accompanied by changes in composition and physical properties such
as grain size, surface temperature, and porosity (compaction).Comment: Meteoritics and Planetary Science; Dawn at Ceres special issu
Thermal conductivity in B- and C- phase of UPt_3
Although the superconductivity in UPt_3 is one of the most well studied,
there are still lingering questions about the nodal directions in the B and C
phase in the presence of a magnetic field. Limiting ourselves to the low
temperature regime (T<<Delta(0)), we study the magnetothermal conductivity with
in semiclassical approximation using Volovik's approach. The angular dependence
of the magnetothermal conductivity for an arbitrary field direction should
clarify the nodal structure in UPt_3.Comment: 4 pages, 5 figure
Directional tunnelling spectroscopy of a normal metal--wave superconductor junction
We calculate the normal metal--wave superconductor tunnelling spectrum
for various junction orientations and for two forms of the superconducting gap,
one which allows for point nodes and the other which allows for line nodes. For
a junction oriented with its normal parallel to the ab plane of the tetragonal
superconductor, we find that the tunnelling spectrum is strongly dependent on
orientation in the plane. The spectrum contains two peaks at energies
equivalent to the magnitudes of the gap function in the direction parallel to
the interface normal and in the direction making a angle with the
normal. These two peaks appear in both superconductors with point nodes and
line nodes, but are more prominent in the latter. For the tunnelling along the
c axis, we find a sharp peak at the gap maximum in the conductance spectrum of
the superconductor with line nodes, whereas with point nodes we find a peak
occurring at the value of the gap function along the c axis. We discuss the
relevance of our result to borocarbide systems.Comment: 16 pages, 10 figure
Temperature-dependent Ginzburg-Landau parameter
Taking into account both the orbital and the paramagnetic depairing effects
we derive a simple analytic formula for the temperature dependence of the
Ginzburg-Landau parameter valid in vicinity of field dependent critical
temperature in a type-II superconductor.Comment: 3 pages, no figure
Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta
The detection of olivine on Vesta is interesting because it may provide
critical insights into planetary differentiation early in our Solar System's
history. Ground-based and Hubble Space Telescope (HST) observations of asteroid
(4) Vesta have suggested the presence of olivine on the surface. These
observations were reinforced by the discovery of olivine-rich HED meteorites
from Vesta in recent years. However, analysis of data from NASA's Dawn
spacecraft has shown that this olivine-bearing unit is actually impact melt in
the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed
during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole,
further complicated this picture. Ammannito et al., (2013a) reported the
discovery of local scale olivine-rich units in the form of excavated material
from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here
we explore alternative sources for the olivine in the northern hemisphere of
Vesta by reanalyzing the data from the VIR instrument using laboratory spectral
measurements of meteorites. We suggest that these olivine exposures could be
explained by the delivery of olivine-rich exogenic material. Based on our
spectral band parameters analysis, the lack of correlation between the location
of these olivine-rich terrains and possible mantle-excavating events, and
supported by observations of HED meteorites, we propose that a probable source
for olivine seen in the northern hemisphere are remnants of impactors made of
olivine-rich meteorites. Best match suggests these units are HED material mixed
with either ordinary chondrites, or with some olivine-dominated meteorites such
as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January
2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01
Simplified R-Symmetry Breaking and Low-Scale Gauge Mediation
We argue that some of the difficulties in constructing realistic models of
low-scale gauge mediation are artifacts of the narrow set of models that have
been studied. In particular, much attention has been payed to the scenario in
which the Goldstino superfield in an O'Raifeartaigh model is responsible for
both supersymmetry breaking and R-symmetry breaking. In such models, the
competing problems of generating sufficiently massive gauginos while preserving
an acceptably light gravitino can be quite challenging. We show that by sharing
the burdens of breaking supersymmetry and R-symmetry with a second field, these
problems are easily solved even within the O'Raifeartaigh framework. We present
explicit models realizing minimal gauge mediation with a gravitino mass in the
eV range that are both calculable and falsifiable.Comment: 31 pages, 4 figures, references added, minor change
Multiband superconductivity in the heavy fermion compound PrOs4Sb12
The thermal conductivity of the heavy fermion superconductor PrOs4Sb12 was
measured down to Tc/40 throughout the vortex state. At lowest temperatures and
for magnetic fields H ~ 0.07Hc2, already 40% of the normal state thermal
conductivity is restored. This behaviour (similar to that observed in MgB2) is
a clear signature of multiband superconductivity in this compound.Comment: 12pages, version #1 20\_06\_200
Angular Position of Nodes in the Superconducting Gap of Quasi-2D Heavy-Fermion Superconductor CeCoIn_5
The thermal conductivity of the heavy-fermion superconductor CeCoIn_5 has
been studied in a magnetic field rotating within the 2D planes. A clear
fourfold symmetry of the thermal conductivity which is characteristic of a
superconducting gap with nodes along the (+-pi,+-pi)-directions is resolved.
The thermal conductivity measurement also reveals a first order transition at
H_c2, indicating a Pauli limited superconducting state. These results indicate
that the symmetry most likely belongs to d_{x^2-y^2}, implying that the
anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.Comment: 5 Pages, 4 figure
- …