682 research outputs found
Quasi-Galois Symmetries of the Modular S-Matrix
The recently introduced Galois symmetries of RCFT are generalized, for the
WZW case, to `quasi-Galois symmetries'. These symmetries can be used to derive
a large number of equalities and sum rules for entries of the modular matrix S,
including some that previously had been observed empirically. In addition,
quasi-Galois symmetries allow to construct modular invariants and to relate
S-matrices as well as modular invariants at different levels. They also lead us
to an extremely plausible conjecture for the branching rules of the conformal
embeddings of g into so(dim g).Comment: 20 pages (A4), LaTe
Saddle point states and energy barriers for vortex entrance and exit in superconducting disks and rings
The transitions between the different vortex states of thin mesoscopic
superconducting disks and rings are studied using the non-linear
Ginzburg-Landau functional. They are saddle points of the free energy
representing the energy barrier which has to be overcome for transition between
the different vortex states. In small superconducting disks and rings the
saddle point state between two giant vortex states, and in larger systems the
saddle point state between a multivortex state and a giant vortex state and
between two multivortex states is obtained. The shape and the height of the
nucleation barrier is investigated for different disk and ring configurations.Comment: 10 pages, 18 figure
Twining characters and orbit Lie algebras
We associate to outer automorphisms of generalized Kac-Moody algebras
generalized character-valued indices, the twining characters. A character
formula for twining characters is derived which shows that they coincide with
the ordinary characters of some other generalized Kac-Moody algebra, the
so-called orbit Lie algebra. Some applications to problems in conformal field
theory, algebraic geometry and the theory of sporadic simple groups are
sketched.Comment: 6 pages, LaTeX, Talk given by C. Schweigert at the XXI international
colloquium on group theoretical methods in physics, July 1996, Goslar,
German
Metastability and paramagnetism in superconducting mesoscopic disks
A projected order parameter is used to calculate, not only local minima of
the Ginzburg-Landau energy functional, but also saddle points or energy
barriers responsible for the metastabilities observed in superconducting
mesoscopic disks (Geim et al. Nature {\bf 396}, 144 (1998)). We calculate the
local minima magnetization and find the energetic instability points between
vortex configurations with different vorticity. We also find that, for any
vorticity, the supercurrent can reverse its flow direction on decreasing the
magnetic field before one vortex can escape.Comment: Modified version as to appear in Phys. Rev. Let
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