11,845 research outputs found
Spin(7)-manifolds with three-torus symmetry
Metrics of exceptional holonomy are vacuum solutions to the Einstein
equation. In this paper we describe manifolds with holonomy contained in
Spin(7) preserved by a three-torus symmetry in terms of tri-symplectic geometry
of four-manifolds. These complement examples that have appeared in the context
of domain wall problems in supergravity
Feshbach Resonances and Medium Effects in ultracold atomic Gases
We develop an effective low energy theory for multi-channel scattering of
cold atomic alkali atoms with particular focus on Feshbach resonances. The
scattering matrix is expressed in terms of observables only and the theory
allows for the inclusion of many-body effects both in the open and in the
closed channels.
We then consider the frequency and damping of collective modes for Fermi
gases and demonstrate how medium effects significantly increase the scattering
rate determining the nature of the modes. Our results obtained with no fitting
parameters are shown to compare well with experimental data.Comment: Presented at the 5th workshop on Critical Stability, Erice, Italy
13-17 October 2008. 8 pages, 3 figures. Figure caption correcte
Collective excitations in a fermion-fermion mixture with different Fermi surfaces
In this paper, collective excitations in a homogeneous fermion-fermion
mixture with different Fermi surfaces are studied. In the Fermi liquid phase,
the zero-sound velocity is found to be larger than the largest Fermi velocity.
With attractive interactions, the superfluid phase appears below a critical
temperature, and the phase mode is the low-energy collective excitation. The
velocity of the phase mode is proportional to the geometric mean of the two
Fermi velocities. The difference between the two velocities may serve as a tool
to detect the superfluid phase.Comment: 4 pages. To be published in Phys. Rev.
Homogeneous spaces, multi-moment maps and (2,3)-trivial algebras
For geometries with a closed three-form we briefly overview the notion of
multi-moment maps. We then give concrete examples of multi-moment maps for
homogeneous hypercomplex and nearly Kaehler manifolds. A special role in the
theory is played by Lie algebras with second and third Betti numbers equal to
zero. These we call (2,3)-trivial. We provide a number of examples of such
algebras including a complete list in dimensions up to and including five
Network maps of student work with physics, other sciences, and math in an integrated science course
In 2004 Denmark introduced a compulsory integrated science course the most
popular upper secondary study program. One of the nation-wide course aims are
for students to "achieve knowledge about some of the central scientific issues
and their social, ethical, and historical perspectives". This is to be done via
collaboration between the subjects, and often involves physics and another
scientific subject. The official teaching plans further state that mathematics
must be used for analysing data. We use network analysis to study six different
implementations of the course in terms of the structure of different kinds of
teaching/learning activities. By creating networks maps of each lesson, we show
that teaching/learning activities in the course seldom tends to address how
sciences can work together to solve a problem, but rather stages each natural
science as a distinct and separate activity with a distinct identity.Comment: 4 pages, 3 figures, 1 table, based on poster presented at PERC 2017
(http://www.compadre.org/per/conferences/2017/
Frequency and damping of the Scissors Mode of a Fermi gas
We calculate the frequency and damping of the scissors mode in a classical
gas as a function of temperature and coupling strength. Our results show good
agreement with the main features observed in recent measurements of the
scissors mode in an ultracold gas of Li atoms. The comparison between
theory and experiment involves no fitting parameters and thus allows an
identification of non-classical effects at and near the unitarity limit.Comment: 4 pages, 2 figure
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