Simplicity of twin tree lattices with non-trivial commutation relations

We prove a simplicity criterion for certain twin tree lattices. It applies to all rank two Kac-Moody groups over finite fields with non-trivial commutation relations, thereby yielding examples of simple non-uniform lattices in the product of two trees

Mass endomorphism and spinorial Yamabe type problems on conformally flat manifolds

Let M be a compact manifold equipped with a Riemannian metric g and a spin structure \si. We let \lambda (M,[g],\si)= \inf_{\tilde{g} \in [g]} \lambda_1^+(\tilde{g}) Vol(M,\tilde{g})^{1/n} where $\lambda_1^+(\tilde{g})$ is the smallest positive eigenvalue of the Dirac operator D in the metric $\tilde{g}$. A previous result stated that \lambda(M,[g],\si) \leq \lambda(\mS^n) =\frac{n}{2} \om_n^{{1/n}} where \om_n stands for the volume of the standard n-sphere. In this paper, we study this problem for conformally flat manifolds of dimension n \geq 2 such that D is invertible. E.g. we show that strict inequality holds in dimension $n\equiv 0,1,2\mod 4$ if a certain endomorphism does not vanish. Because of its tight relations to the ADM mass in General Relativity, the endomorphism will be called mass endomorphism. We apply the strict inequality to spin-conformal spectral theory and show that the smallest positive Dirac eigenvalue attains its infimum inside the enlarged volume-1-conformal class of g.Comment: references updated, some typos remove

Second-Order Phase Transition Induced by Deterministic Fluctuations in Aperiodic Eight-State Potts Models

We investigate the influence of aperiodic modulations of the exchange interactions between nearest-neighbour rows on the phase transition of the two-dimensional eight-state Potts model. The systems are studied numerically through intensive Monte Carlo simulations using the Swendsen-Wang cluster algorithm for different aperiodic sequences. The transition point is located through duality relations, and the critical behaviour is investigated using FSS techniques at criticality. While the pure system exhibits a first-order transition, we show that the deterministic fluctuations resulting from the aperiodic coupling distribution are liable to modify drastically the physical properties in the neighbourhood of the transition point. For strong enough fluctuations of the sequence under consideration, a second-order phase transition is induced. The exponents $\beta/\nu$, $\gamma /\nu$ and $(1-\alpha)/\nu$ are obtained at the new fixed point and crossover effects are discussed. Surface properties are also studied.Comment: LaTeX file with EPJB macro package, 11 pages, 16 postscript figures, to appear in Eur. Phys. J.

Efficient Frontier for Robust Higher-order Moment Portfolio Selection

This article proposes a non-parametric portfolio selection criterion for the static asset allocation problem in a robust higher-moment framework. Adopting the Shortage Function approach, we generalize the multi-objective optimization technique in a four-dimensional space using L-moments, and focus on various illustrations of a four-dimensional set of the first four L-moment primal efficient portfolios. our empirical findings, using a large European stock database, mainly rediscover the earlier works by Jean (1973) and Ingersoll (1975), regarding the shape of the extended higher-order moment efficient frontier, and confirm the seminal prediction by Levy and Markowitz (1979) about the accuracy of the mean-variance criterion.Efficient frontier, portfolio selection, robust higher L-moments, shortage function, goal attainment application.

Driven nonlinear dynamics of two coupled exchange-only qubits

Inspired by creation of a fast exchange-only qubit (Medford et al., Phys. Rev. Lett., 111, 050501 (2013)), we develop a theory describing the nonlinear dynamics of two such qubits that are capacitively coupled, when one of them is driven resonantly at a frequency equal to its level splitting. We include conditions of strong driving, where the Rabi frequency is a significant fraction of the level splitting, and we consider situations where the splitting for the second qubit may be the same or different than the first. We demonstrate that coupling between qubits can be detected by reading the response of the second qubit, even when the coupling between them is only of about $1\%$ of their level splittings, and calculate entanglement between qubits. Patterns of nonlinear dynamics of coupled qubits and their entanglement are strongly dependent on the geometry of the system, and the specific mechanism of inter-qubit coupling deeply influences dynamics of both qubits. In particular, we describe the development of irregular dynamics in a two-qubit system, explore approaches for inhibiting it, and demonstrate existence of an optimal range of coupling strength maintaining stability during the operational time.Comment: 11 pages, 6 figures; One additional figure with changes to the text about the results. Additional references include

Stratégie de rupture basée sur des innovations radicales : Etude du cas de l'entreprise Salomon à la lumière de ses compétences et capacités organisationnelles

This paper concentrates on the analysis of organizational resources, competencies and capabilities as well as on the organizational architectures which facilitate their acquisition and use. On the basis of these concepts, the paper proposes an analysis grid which is then applied to a case study of Salomon, world leader in the winter sports equipment market. This grid is used to gain an understanding of Salomon's success in implementing breakthrough strategies based on radical innovations. Focusing on the study of internal resources leads to an investigation into Salomon's learning capabilities.organizational competency; organizational capabilities; innovation; Salomon

D'un multiple conditionnel en assurance de portefeuille : CAViaR pour les gestionnaires ?

URL des Documents de travail : http://ces.univ-paris1.fr/cesdp/CESFramDP2009.htmClassification JEL : G11, C13, C14, C22, C32.Documents de travail du Centre d'Economie de la Sorbonne 2009.33 - ISSN : 1955-611XIn a Constant Proportion Portfolio Insurance (CPPI) framework, a constant risk exposure is defined by the multiple of the strategy. This article proposes an alternative conditional multiple estimation model, which is based on an autoregressive quantile regression dynamic approach. We estimate several specifications of the conditional multiple model on the American equity market, and we compare relative performances of cushioned portfolios using conditional and unconditional multiples.Dans le cadre de l'assurance de portefeuille à coussin, le multiple garantit une exposition constante au risque. Nous proposons une méthode alternative d'estimation conditionnelle de ce multiple, basée sur une modélisation dynamique du centile et la méthode de régression sur quantile. Après avoir estimé différentes versions de notre modèle sur le marché des actions américaines, nous comparons les performances relatives des portefeuilles gérés avec des multiples conditionnels et inconditionnels