14,880 research outputs found
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
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 (), 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 to these clusters and, moreover, present new
results for the geometric domains for both 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 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 diabĂšte gestationnel (DG) est une complication frĂ©quente de la grossesse. Sa prĂ©valence varie fortement selon la stratĂ©gie de dĂ©pistage utilisĂ©e ainsi que la population Ă©tudiĂ©e. Le DG expose Ă un haut risque de complications, Ă la fois sur le plan maternel et foetal. Ces complications sont en relation directe avec lâhyperglycĂ©mie maternelle, mais cette relation est linĂ©aire, sans valeur-seuil clairement dĂ©finie. Cela explique sans doute pourquoi il est difficile dâĂ©noncer des critĂšres indiscutables de diagnostic du DG. De nombreuses controverses existent depuis plusieurs annĂ©es dans la littĂ©rature quant aux mĂ©thodes les plus adĂ©quates pour dĂ©pister le DG. Les questions sont relatives Ă lâintĂ©rĂȘt dâune mĂ©thode en une ou deux Ă©tapes, au test Ă utiliser en prioritĂ©, aux valeursseuil Ă considĂ©rer en fonction du test retenu ainsi quâau choix dâun dĂ©pistage universel ou uniquement ciblĂ© sur les femmes Ă risque. Un groupe dâexperts internationaux a proposĂ© rĂ©cemment un dĂ©pistage universel du DG avec la rĂ©alisation dâune hyperglycĂ©mie provoquĂ©e par voie orale de 2 heures. Une harmonisation des approches diagnostiques du DG est, en effet, indispensable. Cette vignette clinique discute les avantages et dĂ©savantages des diffĂ©rentes stratĂ©gies proposĂ©es pour dĂ©pister 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 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 compared to the
atomic shot noise level.Comment: 4 pages, 2 figures, revtex
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