17,495 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
Tunable orbital susceptibility in - tight-binding models
We study the importance of interband effects on the orbital susceptibility of
three bands - tight-binding models. The particularity of
these models is that the coupling between the three energy bands (which is
encoded in the wavefunctions properties) can be tuned (by a parameter )
without any modification of the energy spectrum. Using the gauge-invariant
perturbative formalism that we have recently developped, we obtain a generic
formula of the orbital susceptibility of - tight-binding
models. Considering then three characteristic examples that exhibit either
Dirac, semi-Dirac or quadratic band touching, we show that by varying the
parameter and thus the wavefunctions interband couplings, it is
possible to drive a transition from a diamagnetic to a paramagnetic peak of the
orbital susceptibility at the band touching. In the presence of a gap
separating the dispersive bands, we show that the susceptibility inside the gap
exhibits a similar dia to paramagnetic transition.Comment: 15 pages,5 figs. Proceedings of the International Workshop on Dirac
Electrons in Solids 2015Proceedings of the International Workshop on Dirac
Electrons in Solids 201
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
Topological Kondo effect with Majorana fermions
The Kondo effect is a striking consequence of the coupling of itinerant
electrons to a quantum spin with degenerate energy levels. While degeneracies
are commonly thought to arise from symmetries or fine-tuning of parameters, the
recent emergence of Majorana fermions has brought to the fore an entirely
different possibility: a "topological degeneracy" which arises from the
nonlocal character of Majorana fermions. Here we show that nonlocal quantum
spins formed from these degrees of freedom give rise to a novel "topological
Kondo effect". This leads to a robust non-Fermi liquid behavior, known to be
difficult to achieve in the conventional Kondo context. Focusing on mesoscopic
superconductor devices, we predict several unique transport signatures of this
Kondo effect, which would demonstrate the non-local quantum dynamics of
Majorana fermions, and validate their potential for topological quantum
computation
Paying a Visit: The Dalai Lama Effect on International Trade
The Chinese government frequently threatens that meetings between its trading partnersâ officials and the Dalai Lama will be met with animosity and ultimately harm trade ties with China. We run a gravity model of exports to China from 159 partner countries between 1991 and 2008 to test to which extent bilateral tensions affect trade with autocratic China. In order to account for the potential endogeneity of meetings with the Dalai Lama, the number of Tibet Support Groups and the travel pattern of the Tibetan leader are used as instruments. Our empirical results support the idea that countries officially receiving the Dalai Lama at the highest political level are punished through a reduction of their exports to China. However, this âDalai Lama Effectâ is only observed for the Hu Jintao era and not for earlier periods. Furthermore, we find that this effect is mainly driven by reduced exports of machinery and transport equipment and that it disappears two years after a meeting took place.Dalai Lam
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