Testing gravity law in the solar system

The predictions of General relativity (GR) are in good agreement with observations in the solar system. Nevertheless, unexpected anomalies appeared during the last decades, along with the increasing precision of measurements. Those anomalies are present in spacecraft tracking data (Pioneer and flyby anomalies) as well as ephemerides. In addition, the whole theory is challenged at galactic and cosmic scales with the dark matter and dark energy issues. Finally, the unification in the framework of quantum field theories remains an open question, whose solution will certainly lead to modifications of the theory, even at large distances. As long as those "dark sides" of the universe have no universally accepted interpretation nor are they observed through other means than the gravitational anomalies they have been designed to cure, these anomalies may as well be interpreted as deviations from GR. In this context, there is a strong motivation for improved and more systematic tests of GR inside the solar system, with the aim to bridge the gap between gravity experiments in the solar system and observations at much larger scales. We review a family of metric extensions of GR which preserve the equivalence principle but modify the coupling between energy and curvature and provide a phenomenological framework which generalizes the PPN framework and "fifth force" extensions of GR. We briefly discuss some possible observational consequences in connection with highly accurate ephemerides.Comment: Proceedings of Journ\'ees 2010 "Syst\`emes de r\'ef\'erence spatio-temporels", New challenges for reference systems and numerical standards in astronom

Properties of simulated Milky Way-mass galaxies in loose group and field environments

We test the validity of comparing simulated field disk galaxies with the empirical properties of systems situated within environments more comparable to loose groups, including the Milky Way's Local Group. Cosmological simulations of Milky Way-mass galaxies have been realised in two different environment samples: in the field and in environments with similar properties to the Local Group. Apart from the environments of the galaxies, the samples are kept as homogeneous as possible with equivalent ranges in last major merger time, halo mass and halo spin. Comparison of these two samples allow for systematic differences in the simulations to be identified. Metallicity gradients, disk scale lengths, colours, magnitudes and age-velocity dispersion relations are studied for each galaxy in the suite and the strength of the link between these and environment of the galaxies is studied. The bulge-to-disk ratio of the galaxies show that these galaxies are less spheroid dominated than many other simulated galaxies in literature with the majority of both samples being disk dominated. We find that secular evolution and mergers dominate the spread of morphologies and metallicity gradients with no visible differences between the two environment samples. In contrast with this consistency in the two samples there is tentative evidence for a systematic difference in the velocity dispersion-age relations of galaxies in the different environments. Loose group galaxies appear to have more discrete steps in their velocity dispersion-age relations. We conclude that at the current resolution of cosmological galaxy simulations field environment galaxies are sufficiently similar to those in loose groups to be acceptable proxies for comparison with the Milky Way provided that a similar assembly history is considered.Comment: 16 pages, 11 figures, abstract abridged for arXiv. Accepted for publication in Astronomy & Astrophysic

Back-action cancellation in interferometers by quantum locking

We show that back-action noise in interferometric measurements such as gravitational-waves detectors can be completely suppressed by a local control of mirrors motion. An optomechanical sensor with an optimized measurement strategy is used to monitor mirror displacements. A feedback loop then eliminates radiation-pressure effects without adding noise. This very efficient technique leads to an increased sensitivity for the interferometric measurement, which becomes only limited by phase noise. Back-action cancellation is furthermore insensitive to losses in the interferometer.Comment: 4 pages, 3 figures, RevTe

Quantum fluctuations for drag free geodesic motion

The drag free technique is used to force a proof mass to follow a geodesic motion. The mass is protected from perturbations by a cage, and the motion of the latter is actively controlled to follow the motion of the proof mass. We present a theoretical analysis of the effects of quantum fluctuations for this technique. We show that a perfect drag free operation is in principle possible at the quantum level, in spite of the back action exerted on the mass by the position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change

Beating quantum limits in interferometers with quantum locking of mirrors

The sensitivity in interferometric measurements such as gravitational-wave detectors is ultimately limited by quantum noise of light. We discuss the use of feedback mechanisms to reduce the quantum effects of radiation pressure. Recent experiments have shown that it is possible to reduce the thermal motion of a mirror by cold damping. The mirror motion is measured with an optomechanical sensor based on a high-finesse cavity, and reduced by a feedback loop. We show that this technique can be extended to lock the mirror at the quantum level. In gravitational-waves interferometers with Fabry-Perot cavities in each arms, it is even possible to use a single feedback mechanism to lock one cavity mirror on the other. This quantum locking greatly improves the sensitivity of the interferometric measurement. It is furthermore insensitive to imperfections such as losses in the interferometer

On testing the violation of the Clausius inequality in nanoscale electric circuits

The Clausius inequality, one of the classical formulations of the second law, was recently found to be violated in the quantum regime. Here this result is formulated in the context of a mesoscopic or nanoscale linear RLC circuit interacting with a thermal bath. Previous experiments in this and related fields are analyzed and possibilities of experimental detection of the violation are pointed out. It is discussed that recent experiments reached the range of temperatures, where the effect should be visible, and that a part of the proposal was already confirmed.Comment: 5 pages revtex 4. No figure

Pioneer 10 data analysis: Investigation on periodic anomalies

International audienceThe Pioneer Anomaly refers to the difference between the expected theoretical tra jectory of the Pioneer 10 and 11 spacecrafts and the observed tra jectory through Doppler measurements. It has been interpreted by the Jet Propulsion Laboratory (JPL) as a constant anomalous acceleration (Anderson et al. 2002). For this analysis, the Groupe Anomalie Pioneer (GAP) composed of several french laboratories has developped a specific tra jectography software, ODYSSEY, which enables to test different anomaly models. The paper will present, after a brief description of the software and the implemented models, the last results obtained: in addition to the constant anomaly, time dependent signatures of the anomaly have been noticed which can be described geometrically. The fit of the Pioneer 10 data with these new models yields a reduction of the standard deviation of the residual by a factor 2 with respect to the simple constant anomaly

Pioneer 10 Doppler data analysis: disentangling periodic and secular anomalies

This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data analysis as independent as possible from that of J. Anderson et al. \citep{anderson}, using the same data set. A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8 nms$^{-2}$ compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azimuthal angle $\varphi$ defined by the directions Sun-Earth Antenna and Sun-Pioneer. An improved fit is obtained with periodic variations written as the sum of a secular acceleration and two sinusoids of the angles $\varphi$ and $2\varphi$. The tests which have been performed for assessing the robustness of these results are presented.Comment: 13 pages, 6 figures, minor amendment