Cold Atom Clock Test of Lorentz Invariance in the Matter Sector

We report on a new experiment that tests for a violation of Lorentz invariance (LI), by searching for a dependence of atomic transition frequencies on the orientation of the spin of the involved states (Hughes-Drever type experiment). The atomic frequencies are measured using a laser cooled $^{133}$Cs atomic fountain clock, operating on a particular combination of Zeeman substates. We analyze the results within the framework of the Lorentz violating standard model extension (SME), where our experiment is sensitive to a largely unexplored region of the SME parameter space, corresponding to first measurements of four proton parameters and improvements by 11 and 13 orders of magnitude on the determination of four others. In spite of the attained uncertainties, and of having extended the search into a new region of the SME, we still find no indication of LI violation.Comment: 4 pages, accepted for Physical Review Letter

The Isometries of Low-Energy Heterotic M-Theory

We study the effective D=4, N=1 supergravity description of five-dimensional heterotic M-theory in the presence of an M5 brane, and derive the Killing vectors and isometry group for the Kahler moduli-space metric. The group is found to be a non-semisimple maximal parabolic subgroup of Sp(4,R), containing a non-trivial SL(2,R) factor. The underlying moduli-space is then naturally realised as the group space Sp(4,R)/U(2), but equipped with a nonhomogeneous metric that is invariant only under that maximal parabolic group. This nonhomogeneous metric space can also be derived via field truncations and identifications performed on Sp(8,R)/U(4) with its standard homogeneous metric. In a companion paper we use these symmetries to derive new cosmological solutions from known ones.Comment: 11 pages, 1 table; two foonotes added, minor corrections to conten

Domain size heterogeneity in the Ising model: geometrical and thermal transitions

A measure of cluster size heterogeneity ($H$), introduced by Lee et al [Phys. Rev. E {\bf 84}, 020101 (2011)] in the context of explosive percolation, was recently applied to random percolation and to domains of parallel spins in the Ising and Potts models. It is defined as the average number of different domain sizes in a given configuration and a new exponent was introduced to explain its scaling with the size of the system. In thermal spin models, however, physical clusters take into account the temperature-dependent correlation between neighboring spins and encode the critical properties of the phase transition. We here extend the measure of $H$ to these clusters and, moreover, present new results for the geometric domains for both $d=2$ and 3. We show that the heterogeneity associated with geometric domains has a previously unnoticed double peak, thus being able to detect both the thermal and percolative transition. An alternative interpretation for the scaling of $H$ that does not introduce a new exponent is also proposed.Comment: 7 pages, 4 figure

Diagnosis of gestational diabetes

peer reviewedGestational diabetes (GD) is a common complication of pregnancy. Its prevalence depends on the strategy used for screening and the studied population. Pregnant women with GD are at increased risk for maternal and fetal complications. The relationship between maternal blood sugar and complications is linear, without a clear threshold defining GD. Therefore, the diagnostic criteria for GD have been the subject of several controversies since many years. The choice of the one-step or two-step method, the test to be used and the cut-off levels validated to define GD are still debated. The same is true regarding a universal versus a at-risk population screening. International experts have recently proposed the use of a one-step approach with a 2-hour oral glucose tolerance test for a universal screening. The need for a better harmonization regarding the diagnosis of GD is indeed mandatory. The present article discusses both the advantages and disadvantages of the various approaches used for GD screening.Le diabète gestationnel (DG) est une complication fréquente de la grossesse. Sa prévalence varie fortement selon la stratégie de dépistage utilisée ainsi que la population étudiée. Le DG expose à un haut risque de complications, à la fois sur le plan maternel et foetal. Ces complications sont en relation directe avec l’hyperglycémie maternelle, mais cette relation est linéaire, sans valeur-seuil clairement définie. Cela explique sans doute pourquoi il est difficile d’énoncer des critères indiscutables de diagnostic du DG. De nombreuses controverses existent depuis plusieurs années dans la littérature quant aux méthodes les plus adéquates pour dépister le DG. Les questions sont relatives à l’intérêt d’une méthode en une ou deux étapes, au test à utiliser en priorité, aux valeursseuil à considérer en fonction du test retenu ainsi qu’au choix d’un dépistage universel ou uniquement ciblé sur les femmes à risque. Un groupe d’experts internationaux a proposé récemment un dépistage universel du DG avec la réalisation d’une hyperglycémie provoquée par voie orale de 2 heures. Une harmonisation des approches diagnostiques du DG est, en effet, indispensable. Cette vignette clinique discute les avantages et désavantages des différentes stratégies proposées pour dépister le DG

Stability of atomic clocks based on entangled atoms

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of $N$ atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as $N^{1/6}$ compared to the atomic shot noise level.Comment: 4 pages, 2 figures, revtex