A Double Auction Market with Signals of Varying Precision

A computerized double auction market with human traders is employed to examine the relation of price and volume under conditions of asymmetric information. In this market, the informed traders receive higher precision signals than the uninformed traders. The relation of price and volume has been suggested as an important factor in the process of information revelation whereby information held by informed traders is transferred to uninformed traders. In contrast, the no-trade theorems suggest that trade should not occur at all between informed and uninformed traders. The results show trading volume within the informed group to be positively correlated with signal precision. In situations of asymmetric information, uninformed trading activity as measured by volume/precision correlations declines significantly as the precision of the signals of informed traders increases. However, the presence of asymmetric information does not lead to a zero trade condition for either the informed or the uninformed traders.Experimental, Double Auction, Information Precision, Trading Volume, Asymmetric Information

Frontier impedance effects and the growth of international exchanges: an empirical analysis for France

On the European Union scale, international traffic is growing faster than intra-national traffic. This phenomenon is often viewed as a consequence of the abatement of the frontier effect. In this article the frontier effect is analyzed, on the basis of data available for road traffic between France and its neighbors and of freight transport data available at the EU level. The concept is discussed in the light of this empirical analysis. The shortcomings of the static approach lead to a critical revaluation by means of a longitudinal approach. In the conclusion some potential directions for future research are discussed.Frontier ; frontier effect ; international flow ; passengers transport ; goods transport ; Europe

Combined analytical and numerical approach to magnetization plateaux in one-dimensional spin tube antiferromagnets

In this paper, we investigate the properties of frustrated three-leg spin tubes under a magnetic field. We concentrate on two kind of geometries for these tubes, one of which is relevant for the compound $\mathrm{[(CuCl_2tachH)_3Cl]Cl_2}$. We combine an analytical path integral approach with a strong coupling approach, as well as large-scale Density Matrix Renormalization Groups (DMRG) simulations, to identify the presence of plateaux in the magnetization curve as a function of the value of spin $S$. We also investigate the issue of gapless non-magnetic excitations on some plateaux, dubbed chirality degrees of freedom for both tubes.Comment: 17 page

Magnetization plateaus of an easy-axis Kagom\'e antiferromagnet with extended interactions

We investigate the properties in finite magnetic field of an extended anisotropic XXZ spin-1/2 model on the Kagome lattice, originally introduced by Balents, Fisher, and Girvin [Phys. Rev. B, 65, 224412 (2002)]. The magnetization curve displays plateaus at magnetization m=1/6 and 1/3 when the anisotropy is large. Using low-energy effective constrained models (quantum loop and quantum dimer models), we discuss the nature of the plateau phases, found to be crystals that break discrete rotation and/or translation symmetries. Large-scale quantum Monte-Carlo simulations were carried out in particular for the m=1/6 plateau. We first map out the phase diagram of the effective quantum loop model with an additional loop-loop interaction to find stripe order around the point relevant for the original model as well as a topological Z2 spin liquid. The existence of a stripe crystalline phase is further evidenced by measuring both standard structure factor and entanglement entropy of the original microscopic model.Comment: 14 pages, 14 figure

Colour-dressed hexagon tessellations for correlation functions and non-planar corrections

We continue the study of four-point correlation functions by the hexagon tessellation approach initiated in 1611.05436 and 1611.05577. We consider planar tree-level correlation functions in $\mathcal{N} = 4$ supersymmetric Yang-Mills theory involving two non-protected operators. We find that, in order to reproduce the field theory result, it is necessary to include $SU(N)$ colour factors in the hexagon formalism; moreover, we find that the hexagon approach as it stands is naturally tailored to the single-trace part of correlation functions, and does not account for multi-trace admixtures. We discuss how to compute correlators involving double-trace operators, as well as more general $1/N$ effects; in particular we compute the whole next-to-leading order in the large-$N$ expansion of tree-level BMN two-point functions by tessellating a torus with punctures. Finally, we turn to the issue of "wrapping", L\"uscher-like corrections. We show that $SU(N)$ colour-dressing reproduces an earlier empirical rule for incorporating single-magnon wrapping, and we provide a direct interpretation of such wrapping processes in terms of $\mathcal{N}=2$ supersymmetric Feynman diagrams.Comment: 42 pages, typos correcte

Transportation and access to urban services in Dar es Salaam

Transportation in Dar es Salaam is particularly difficult. Statistical data drawn from the 1993 Human Resources Development Survey confirm that in unplanned settlements, transportation conditions and access to urban services are less favourable than in the rest of the city. The poverty of a majority of city inhabitants, the low quality of urban passenger transport and poor accessibility result in daily mobility reduced to the immediate neighbourhood, while in turn tends to perpetuate poverty.Access to urban services ; daily mobility ; Statistical data (HRDS 1993) ; poverty ; Dar es Salaam

Universal logarithmic corrections to entanglement entropies in two dimensions with spontaneously broken continuous symmetries

We explore the R\'enyi entanglement entropies of a one-dimensional (line) subsystem of length $L$ embedded in two-dimensional $L\times L$ square lattice for quantum spin models whose ground-state breaks a continuous symmetry in the thermodynamic limit. Using quantum Monte Carlo simulations, we first study the $J_1 - J_2$ Heisenberg model with antiferromagnetic nearest-neighbor $J_1>0$ and ferromagnetic second-neighbor couplings $J_2\le 0$. The signature of SU(2) symmetry breaking on finite size systems, ranging from $L=4$ up to $L=40$ clearly appears as a universal additive logarithmic correction to the R\'enyi entanglement entropies: $l_q \ln L$ with $l_q\simeq 1$, independent of the R\'enyi index and values of $J_2$. We confirm this result using a high precision spin-wave analysis (with restored spin rotational symmetry) on finite lattices up to $10^5\times 10^5$ sites, allowing to explore further non-universal finite size corrections and study in addition the case of U(1) symmetry breaking. Our results fully agree with the prediction $l_q=n_G/2$ where $n_G$ is the number of Goldstone modes, by Metlitski and Grover [arXiv:1112.5166].Comment: 6 pages, 6 figure

Selection of factorizable ground state in a frustrated spin tube: Order by disorder and hidden ferromagnetism

The interplay between frustration and quantum fluctuation in magnetic systems is known to be the origin of many exotic states in condensed matter physics. In this paper, we consider a frustrated four-leg spin tube under a magnetic field. This system is a prototype to study the emergence of a nonmagnetic ground state factorizable into local states and the associated order parameter without quantum fluctuation, that appears in a wide variety of frustrated systems. The one-dimensional nature of the system allows us to apply various techniques: a path-integral formulation based on the notion of order by disorder, strong-coupling analysis where magnetic excitations are gapped, and density-matrix renormalization group. All methods point toward an interesting property of the ground state in the magnetization plateaus, namely, a quantized value of relative magnetizations between different sublattices (spin imbalance) and an almost perfect factorization of the ground state

Improving entanglement and thermodynamic R\'enyi entropy measurements in quantum Monte Carlo

We present a method for improving measurements of the entanglement R\'enyi entropies in quantum Monte Carlo simulations by relating them with measurements of participation R\'enyi entropies. Exploiting the capability of building improved estimators for the latter allows to obtain very good estimates for entanglement R\'enyi entropies. When considering a full system instead of a bipartition, the method can be further ameliorated providing access to the thermodynamic R\'enyi entropies with high accuracy. We also explore a recently-proposed method for the reconstruction of the entanglement spectrum from entanglement R\'enyi entropies and finally show how potential entanglement Hamiltonians may be tested for their validity using a comparison with thermal R\'enyi entropies.Comment: 15 pages, 11 figure