48 research outputs found
Violation of the equivalence principle from light scalar fields: from Dark Matter candidates to scalarized black holes
Tensor-scalar theory is a wide class of alternative theory of gravitation
that can be motivated by higher dimensional theories, by models of dark matter
or dark ernergy. In the general case, the scalar field will couple
non-universally to matter producing a violation of the equivalence principle.
In this communication, we review a microscopic model of scalar/matter coupling
and its observable consequences in terms of universality of free fall, of
frequencies comparison and of redshifts tests. We then focus on two models: (i)
a model of ultralight scalar dark matter and (ii) a model of scalarized black
hole in our Galactic Center. For both these models, we present constraints
using recent measurements: atomic clocks comparisons, universality of free fall
measurements, measurement of the relativistic redshift with the short period
star S0-2 orbiting the supermassive black hole in our Galactic Center.Comment: 8 pages, 1 figure, contribution to the 2019 Gravitation session of
the 54th Rencontres de Morion
Bandit problems with fidelity rewards
The fidelity bandits problem is a variant of the K-armed bandit problem in which the reward of each arm is augmented by a fidelity reward that provides the player with an additional payoff depending on how âloyalâ the player has been to that arm in the past. We propose two models for fidelity. In the loyalty-points model the amount of extra reward depends on the number of times the arm has previously been played. In the subscription model the additional reward depends on the current number of consecutive draws of the arm. We consider both stochastic and adversarial problems. Since single-arm strategies are not always optimal in stochastic problems, the notion of regret in the adversarial setting needs careful adjustment. We introduce three possible notions of regret and investigate which can be bounded sublinearly. We study in detail the special cases of increasing, decreasing and coupon (where the player gets an additional reward after every m plays of an arm) fidelity rewards. For the models which do not necessarily enjoy sublinear regret, we provide a worst case lower bound. For those models which exhibit sublinear regret, we provide algorithms and bound their regret
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International audienceThe GANIL facility consists of three successive cyclotrons. The tuning of these cyclotrons and of the transfer beam lines isachieved in about 24 hours. Reducing this setting time would enable to increase the time allocated to physics experiments.New tools are realized for automatic beam tuning. These tools are expected to make the tuning easier, shorter and morereproducible
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International audienceThe GANIL facility consists of three successive cyclotrons. The tuning of these cyclotrons and of the transfer beam lines isachieved in about 24 hours. Reducing this setting time would enable to increase the time allocated to physics experiments.New tools are realized for automatic beam tuning. These tools are expected to make the tuning easier, shorter and morereproducible
Low-Rank Network Decomposition Reveals Structural Characteristics Of Small-World Networks
Small-world networks occur naturally throughout biological, technological, and social systems. With their prevalence, it is particularly important to prudently identify small-world networks and further characterize their unique connection structure with respect to network function. In this work we develop a formalism for classifying networks and identifying small-world structure using a decomposition of network connectivity matrices into low-rank and sparse components, corresponding to connections within clusters of highly connected nodes and sparse interconnections between clusters, respectively. We show that the network decomposition is independent of node indexing and define associated bounded measures of connectivity structure, which provide insight into the clustering and regularity of network connections. While many existing network characterizations rely on constructing benchmark networks for comparison or fail to describe the structural properties of relatively densely connected networks, our classification relies only on the intrinsic network structure and is quite robust with respect to changes in connection density, producing stable results across network realizations. Using this framework, we analyze several real-world networks and reveal new structural properties, which are often indiscernible by previously established characterizations of network connectivity
Discovery of a weak magnetic field in the photosphere of the single giant Pollux
Aims: We observe the nearby, weakly-active single giant, Pollux, in order to
directly study and infer the nature of its magnetic field. Methods: We used the
new generation spectropolarimeters ESPaDOnS and NARVAL to observe and detect
circular polarization within the photospheric absorption lines of Pollux. Our
observations span 18 months from 2007-2009. We treated the spectropolarimetric
data using the Least-Squares Deconvolution method to create high
signal-to-noise ratio mean Stokes V profiles. We also measured the classical
activity indicator S-index for the Ca H&K lines, and the stellar radial
velocity (RV). Results: We have unambiguously detected a weak Stokes V signal
in the spectral lines of Pollux, and measured the related surface-averaged
longitudinal magnetic field Bl. The longitudinal field averaged over the span
of the observations is below one gauss. Our data suggest variations of the
longitudinal magnetic field, but no significant variation of the S-index. We
observe variations of RV which are qualitatively consistent with the published
ephemeris for a proposed exoplanet orbiting Pollux. The observed variations of
Bl appear to mimic those of RV, but additional data for this relationship to be
established. Using evolutionary models including the effects of rotation, we
derive the mass of Pollux and we discuss its evolutionary status and the origin
of its magnetic field. Conclusions: This work presents the first direct
detection of the magnetic field of Pollux, and demonstrates that ESPaDOnS and
NARVAL are capable of obtaining sub-G measurements of the surface-averaged
longitudinal magnetic field of giant stars, and of directly studying the
relationships between magnetic activity, stellar evolution and planet hosting
of these stars.Comment: 8 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
SPIRAL II Project (electron option) - Preliminary Design Study
This document presents a Preliminary Design Study (PDS) of the electron option of the SPIRAL II project
POST-ACCELERATION OF HIGH INTENSITY RIB THROUGH THE CIME CYCLOTRON IN THE FRAME OF THE SPIRAL2 PROJECT AT GANIL
The cyclotron CIME is presently used at GANIL for
the acceleration of SPIRAL1 radioactive beams. One of
the goals of the SPIRAL2 project is to produce, postaccelerate
and use in the existing experimental areas
much higher intensity secondary beams induced by
uranium fission like neutron-rich krypton, xenon, tin
isotopes, and many others. Intensity may reach 1010 pps.
Specific developments are needed for secondary beam
diagnostics. Improvement of mass separation is also
necessary, and the Vertical Mass Separator (VMS) is
specially developed for this purpose.
However, the main concern is related to the high
radioactivity linked to RIB high intensity. Safety and
radioprotection issues will require modifications of the
installation with special care for the maintenance of the
cyclotron. The experience of the SPIRAL1 beams, in
terms of beam losses and equipment contamination, is
especially useful to define the necessary modificationsIMP;Chinese Academy of Science