7,342 research outputs found
Index realization for automorphisms of free groups
For any surface of genus and (essentially) any collection
of positive integers with Masur and Smillie have shown that there exists a pseudo-Anosov
homeomorphism with precisely singularities in its stable foliation , such that has
precisely separatrices raying out from each .
In this paper we prove the analogue of this result for automorphisms of a
free group , where "pseudo-Anosov homeomorphism" is replaced by "fully
irreducible automorphism" and the Gauss-Bonnet equality is replaced by the index inequality from
Gaboriau, Jaeger, Levitt and Lustig.Comment: 19 pages, 3 figures, 1 table, revised version for publicatio
Transmission of ultracold atoms through a micromaser: detuning effects
The transmission probability of ultracold atoms through a micromaser is
studied in the general case where a detuning between the cavity mode and the
atomic transition frequencies is present. We generalize previous results
established in the resonant case (zero detuning) for the mesa mode function. In
particular, it is shown that the velocity selection of cold atoms passing
through the micromaser can be very easily tuned and enhanced using a
non-resonant field inside the cavity. Also, the transmission probability
exhibits with respect to the detuning very sharp resonances that could define
single cavity devices for high accuracy metrology purposes (atomic clocks).Comment: 5 pages, 7 figure
Phase Diagram for a Luttinger Liquid coupled to Phonons in one dimension
The Green function and the ordering correlation functions of a system of
electrons coupled to acoustic phonons are calculated explicitly. The
sensitivity of the correlation function exponents to the Wentzel-Bardeen
singularity is discussed. A phase diagram is established for the Hubbard model
coupled to phonons, using the integral equations of Lieb and Wu. By increasing
the filling factor towards half filling, the Wentzel-Bardeen singularity can be
reached for arbitrary phonon coupling. This suppresses antiferromagnetic
fluctuations and drives the system in a metallic phase, and ultimately in the
triplet superconducting regime.Comment: 33 pages, REVTex, 6 figures upon request ([email protected]
Positive and negative Hanbury-Brown and Twiss correlations in normal metal-superconducting devices
In the light of the recent analogs of the Hanbury--Brown and Twiss
experiments in mesoscopic beam splitters, negative current noise correlations
are recalled to be the consequence of an exclusion principle. Here, positive
(bosonic) correlations are shown to exist in a fermionic system, composed of a
superconductor connected to two normal reservoirs. In the Andreev regime, the
correlations can either be positive or negative depending on the reflection
coefficient of the beam splitter. For biases beyond the gap, the transmission
of quasiparticles favors fermionic correlations. The presence of disorder
enhances positive noise correlations. Potential experimental applications are
discussed.Comment: 4 pages, 3 figures, RevTeX, revised versio
A universality property for last-passage percolation paths close to the axis
We consider a last-passage directed percolation model in , with i.i.d.
weights whose common distribution has a finite th moment. We study the
fluctuations of the passage time from the origin to the point
. We show that, for suitable (depending
on ), this quantity, appropriately scaled, converges in distribution as
to the Tracy-Widom distribution, irrespective of the underlying
weight distribution. The argument uses a coupling to a Brownian directed
percolation problem and the strong approximation of Koml\'os, Major and
Tusn\'ady.Comment: 8 page
Channels of international risk-sharing: capital gains versus income flows
Global financial integration unlocks a huge potential for international risk sharing. We examine the degree to which international equity holdings act as a risk sharing device in industrial and emerging economies. We split equity returns into investment income (dividend distribution) and capital gains to investigate which of the two channels delivers the largest potential for risk sharing. Our evidence suggests that net capital gains are a more potent channel of risk sharing. They behave in a countercyclical way, that is they tend to be positive (negative) when the domestic economy is growing more slowly (rapidly) than the rest of the world. Countries with more countercyclical net capital gains experience improved consumption risk sharing. The empirical analysis furthermore suggests that these risk sharing properties of net capital gains have increased through time, in particular in the 1990s and early-2000s, on the back of a declining equity home bias and financial market deepening. JEL Classification: F21, F30, F36consumption smoothing, Cross-Border Investment, International portfolio diversification, International risk sharing, Valuation effects
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