471 research outputs found
The effective action of warped M-theory reductions with higher-derivative terms - Part II
We study the three-dimensional effective action obtained by reducing
eleven-dimensional supergravity with higher-derivative terms on a background
solution including a warp-factor, an eight-dimensional compact manifold, and
fluxes. The dynamical fields are K\"ahler deformations and vectors from the
M-theory three-form. We show that the potential is only induced by fluxes and
the naive contributions obtained from higher-curvature terms on a Calabi-Yau
background vanish once the back-reaction to the full solution is taken into
account. For the resulting three-dimensional action we analyse the K\"ahler
potential and complex coordinates and show compatibility with N=2
supersymmetry. We argue that the higher-order result is also compatible with a
no-scale condition. We find that the complex coordinates should be formulated
as divisor integrals for which a non-trivial interplay between the warp-factor
terms and the higher-curvature terms allow a derivation of the moduli space
metric. This leads us to discuss higher-derivative corrections to the M5-brane
action.Comment: 26 page
On M-theory fourfold vacua with higher curvature terms
We study solutions to the eleven-dimensional supergravity action, including
terms quartic and cubic in the Riemann curvature, that admit an
eight-dimensional compact space. The internal background is found to be a
conformally Kahler manifold with vanishing first Chern class. The metric
solution, however, is non-Ricci-flat even when allowing for a conformal
rescaling including the warp factor. This deviation is due to the possible
non-harmonicity of the third Chern-form in the leading order Ricci-flat metric.
We present a systematic derivation of the background solution by solving the
Killing spinor conditions including higher curvature terms. These are
translated into first-order differential equations for a globally defined real
two-form and complex four-form on the fourfold. We comment on the supersymmetry
properties of the described solutions.Comment: 14 page
Safety Relevant Positioning Applications in Rail Traffic using the European Satellite System "Galileo"
Die Ortung im Eisenbahnverkehr hat eine hohe sicherheitstechnische Relevanz. Eine falsch detektierte Position eines Fahrzeugs kann zu einer erheblichen Gefährdung führen, da die ermittelte Ortsinformation für die Freigabe und das Wiederbesetzen von Gleisabschnitten genutzt wird. Daraus abgeleitet, müssen Ortungssysteme bei der Zulassung unter anderem die folgenden sicherheitskritischen Anforderungen erfüllen Genauigkeit, Zuverlässigkeit, Integrität und Verfügbarkeit der Ortungsinformation, die gemäß SIL 4 nachzuweisen sind
Inducing an optical Feshbach resonance via stimulated Raman coupling
We demonstrate a novel method of inducing an optical Feshbach resonance based
on a coherent free-bound stimulated Raman transition. In our experiment atoms
in a Rb87 Bose-Einstein condensate are exposed to two phase-locked Raman laser
beams which couple pairs of colliding atoms to a molecular ground state. By
controlling the power and relative detuning of the two laser beams, we can
change the atomic scattering length considerably. The dependence of scattering
length on these parameters is studied experimentally and modelled
theoretically.Comment: 8 pages, 8 figures, submitted to PR
Simple fluid with broken time reversal invariance
We characterize a system of hard spheres with a simple collision rule that
breaks time reversal symmetry, but conserves energy. The collisions lead to an
a-chiral, isotropic, and homogeneous stationary state, whose properties are
determined in simulations and compared to an approximate theory originally
developed for elastic hard spheres. In the nonequilibrium fluid state,
velocities are correlated, a phenomenon known from other nonequilibrium
stationary states. The correlations are long-ranged decaying like in
dimensions. Such correlations are expected on general grounds far from
equilibrium and had previously been observed in driven or non-stationary
systems.Comment: 14 pages, 17 Figure
A Reference Architecture for Mobile Knowledge Management
Although mobile knowledge management (mKM) is being perceived as an emerging R&D field, its concepts and approaches are not well-settled, as opposed to the general field of Knowledge Management (KM). In this work, we try to establish a definition for mKM. Taking into account building blocks of KM in enterprises and the abstract use cases of mKM systems we introduce an reference architecture for mKM systems as a basis for verifying and comparing concepts and system architectures. Finally we address the potential of mKM to be suitable as a prototype model for mobile, situation-aware information processing in the field of Ambient Intelligence Environments
Ramping fermions in optical lattices across a Feshbach resonance
We study the properties of ultracold Fermi gases in a three-dimensional
optical lattice when crossing a Feshbach resonance. By using a zero-temperature
formalism, we show that three-body processes are enhanced in a lattice system
in comparison to the continuum case. This poses one possible explanation for
the short molecule lifetimes found when decreasing the magnetic field across a
Feshbach resonance. Effects of finite temperatures on the molecule formation
rates are also discussed by computing the fraction of double-occupied sites.
Our results show that current experiments are performed at temperatures
considerably higher than expected: lower temperatures are required for
fermionic systems to be used to simulate quantum Hamiltonians. In addition, by
relating the double occupancy of the lattice to the temperature, we provide a
means for thermometry in fermionic lattice systems, previously not accessible
experimentally. The effects of ramping a filled lowest band across a Feshbach
resonance when increasing the magnetic field are also discussed: fermions are
lifted into higher bands due to entanglement of Bloch states, in good agreement
with recent experiments.Comment: 9 pages, 7 figure
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