3,509 research outputs found
Phase Diagram of Interacting Bosons on the Honeycomb Lattice
We study the ground state properties of repulsively interacting bosons on the
honeycomb lattice using large-scale quantum Monte Carlo simulations. In the
hard-core limit the half-filled system develops long ranged diagonal order for
sufficiently strong nearest-neighbor repulsion. This staggered solid melts at a
first order quantum phase transition into the superfluid phase, without the
presence of any intermediate supersolid phase. Within the superfluid phase,
both the superfluid density and the compressibility exhibit local minima near
particle- (hole-) density one quarter, while the density and the condensate
fraction show inflection points in this region. Relaxing the hard-core
constraint, supersolid phases emerge for soft-core bosons. The suppression of
the superfluid density is found to persist for sufficiently large, finite
on-site repulsion.Comment: 4 pages with 5 figure
Export and benefits of hedging in emerging economies
We study the impact of exchange rate risk upon export production within an emerging economy lacking in currency forward markets. However there exists a financial asset whose price is correlated with the relevant foreign currency. We present conditions under which export production is stimulated when the hedging device becomes more effective. In any case the exporting firm benefits from imperfectly hedging exchange rate risk. --Emerging markets,transition economy,export,exchange rate risk,price risk,hedging
Export production, hedging exchange rate risk: the duopoly case
This paper studies a Cournot duopoly in international trade so that the firms are exposed to exchange rate risk. A hedging opportunity is introduced by a forward market where the foreign currency can be traded on. We investigate two settings: First we assume that hedging and output decisions are taken simultaneously. We show that hedging is just done for risk managing reasons as it is not possible to use hedging strategically. In this setting the well-known separation result of the competitive firm holds if both firms have the hedging opportunity. In the second setting the hedging decisions are made before the output decisions. We show that hedging is used not only to manage the risk exposure but also as a strategic device. Furthermore we find that no separation result can be stated. --Exchange Rate risk,hedging,exports,duopoly
Corner contribution to the entanglement entropy of strongly-interacting O(2) quantum critical systems in 2+1 dimensions
In a D=2+1 quantum critical system, the entanglement entropy across a
boundary with a corner contains a subleading logarithmic scaling term with a
universal coefficient. It has been conjectured that this coefficient is, to
leading order, proportional to the number of field components N in the
associated O(N) continuum field theory. Using density matrix
renormalization group calculations combined with the powerful numerical linked
cluster expansion technique, we confirm this scenario for the O(2)
Wilson-Fisher fixed point in a striking way, through direct calculation at the
quantum critical points of two very different microscopic models. The value of
this corner coefficient is, to within our numerical precision, twice the
coefficient of the Ising fixed point. Our results add to the growing body of
evidence that this universal term in the R\'enyi entanglement entropy reflects
the number of low-energy degrees of freedom in a system, even for strongly
interacting theories.Comment: 6 pages, 6 figure
An Experimental 11.5 T Nb3Sn LHC Type of Dipole Magnet
As part of the magnet development program for the LHC an experimental 1 m long 11.5 T single aperture Nb3Sn dipole magnet has been designed and is now under construction. The design is focused on full utilisation of the high current density in the powder tube Nb3Sn. A new field optimisation has led to a different winding layout and cable sizes as compared to the reference LHC design. Another important feature of the design is the implementation of a shrink fit ring collar system. An extensive study of the critical current of the Nb3Sn cables as a function of the transverse stress on the cables shows a permanent degradation by the cabling process of about 20%, still leaving a safety margin at the operation field of 11.5 T of 15%. A revised glass/mica glass insulation system is applied which improves the thermal conductivity of the windings as well as the impregnation process considerably. This paper describes various design and production details of the magnet system as well as component test
Polar Molecules with Three-Body Interactions on the Honeycomb Lattice
We study the phase diagram of ultra-cold bosonic polar molecules loaded on a
two-dimensional optical lattice of hexagonal symmetry controlled by external
electric and microwave fields. Following a recent proposal in Nature Physics
\textbf{3}, 726 (2007), such a system is described by an extended Bose-Hubbard
model of hard-core bosons, that includes both extended two- and three-body
repulsions. Using quantum Monte-Carlo simulations, exact finite cluster
calculations and the tensor network renormalization group, we explore the rich
phase diagram of this system, resulting from the strongly competing nature of
the three-body repulsions on the honeycomb lattice. Already in the classical
limit, they induce complex solid states with large unit cells and macroscopic
ground state degeneracies at different fractional lattice fillings. For the
quantum regime, we obtain effective descriptions of the various phases in terms
of emerging valence bond crystal states and quantum dimer models. Furthermore,
we access the experimentally relevant parameter regime, and determine the
stability of the crystalline phases towards strong two-body interactions
The Normative Effect of Article 3.5 TEU: Observance and Development of International Law by the European Union
The Normative Effect of Article 3.5 TEU: Observance and Development of International Law by the European Union
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