arXiv subjects

P. David

Publications and source records attributed to P. David.

34 records · Page 2Linked to original sources

arXiv2015

Tests of gravitation with Gaia observations of Solar System Objects

In this communication, we show how asteroids observations from the Gaia mission can be used to perform local tests of General Relativity (GR). This ESA mission, launched in December 2013, will observe --in addition to the stars-- a large number of small Solar System Objects (SSOs) with unprecedented astrometric precision. Indeed, it is expected that about 360,000 asteroids will be observed with a nominal sub-mas precision. Here, we show how these observations can be used to constrain some extensions to General Relativity. We present results of SSOs simulations that take into account the time sequences over 5 years and geometry of the observations that are particular to Gaia. We present a sensitivity study on various GR extensions and dynamical parameters including: the Sun quadrupolar moment $J_2$, the parametrized post-Newtonian parameter $β$, the Nordtvedt parameter $η$, the fifth force formalism, the Lense-Thirring effect, a temporal variation of the gravitational parameter $GM_\textrm{sun}$ (a linear variation as well as a periodic variation), the Standard Model Extension formalism,... Some implications for planetary ephemerides analysis are also briefly discussed.

gr-qc↗

arXiv2015

The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis

Astrometric observations performed by the Gaia Follow-Up Network for Solar System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects first detected by ESA's Gaia mission remain recoverable after their discovery. An observation campaign on the potentially hazardous asteroid (99 942) Apophis was conducted during the asteroid's latest period of visibility, from 12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall performance of the Gaia-FUN-SSO . The 2732 high quality astrometric observations acquired during the Gaia-FUN-SSO campaign were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric reduction process and the precision of the newly obtained measurements are discussed. We compare the residuals of astrometric observations that we obtained using this reduction process to data sets that were individually reduced by observers and accepted by the Minor Planet Center. We obtained 2103 previously unpublished astrometric positions and provide these to the scientific community. Using these data we show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions. Finally, we discuss the impact of our campaign reduction on the recovery process of newly discovered asteroids.

astro-ph.EP↗

arXiv2013

An Update of the HLS Estimate of the Muon g-2

A global fit of parameters allows us to pin down the Hidden Local Symmetry (HLS) effective Lagrangian, which we apply for the prediction of the leading hadronic vacuum polarization contribution to the muon g-2. The latter is dominated by the annihilation channel e+e- -> pi+pi-, for which data are available by scan (CMD-2 and SND) and ISR (KLOE-2008, KLOE-2010 and BaBar) experiments. It is well known that the different data sets are not in satisfactory agreement. In fact it is possible to fix the model parameters without using the pi+pi- data, by using instead the dipion spectra measured in the tau decays together with experimental spectra for the pi0 gamma, eta gamma, pi+pi-pi0, K+K-, K0bar K0 final states supplemented by specific meson decay properties. Among these, the accepted decay width for rho0 -> e+e- and the partial widths and phase information for the omega/phi -> pi+pi- transitions, are considered. It is then shown that, relying on this global data set, the HLS model, appropriately broken, allows to predict accurately the pion form factor up to 1.05 GeV. It is shown that the data samples provided by CMD-2, SND and KLOE-2010 behave consistently with each other and with the other considered data. Consistency problems with the KLOE-2008 and BaBar data samples are substantiated. "All data" global fits are investigated by applying reweighting the conflicting data sets. Constraining to our best fit, the broken HLS model yields a_mu(th) = (11659169.55 [+1.26 -0.59]_phi +[+0.00 -2.00]_tau +/- 5.21_(th))~10**-10 associated with a very good global fit probability. Correspondingly, we find that Delta a_mu=a_mu (exp)- a_mu (th) exhibits a significance ranging between 4.7 and 4.9 sigma.

hep-ph↗

arXiv2011

Upgraded Breaking Of The HLS Model: A Full Solution to the tau-e+e- and phi Decay Issues And Its Consequences On g-2 VMD Estimates

The muon anomalous magnetic moment $a_μ$ and the hadronic vacuum polarization are examined using data analyzed within the framework of a suitably broken HLS model. The analysis relies on all available scan data samples and leaves provisionally aside the existing ISR data. Our HLS model based global fit approach allows for a better check of consistency between data sets and we investigate how results depend on different strategies which may be followed. Relying on global fit qualities, we find several acceptable solutions leading to ambiguities in the reconstructed value for $(a_μ)_{th}$. Among these, the most conservative solution is $a_μ^{\rm had,LO}[{\rm HLS \ improved}]=687.72(4.63) \times 10^{-10}$ and $(a_μ)_{th}=11\,659\,175.37(5.31)\times 10^{-10}$ corresponding to a $4.1 σ$ significance for the difference $Δa_μ=(a_μ)_{exp}-(a_μ)_{th}$. It is also shown that the various contributions accessible through the model yield uniformly a factor 2 improvement of their uncertainty. The breaking procedure implemented in the HLS model is an extension of the former procedure based on the BKY mechanism. This yields a quite satisfactory simultaneous description of most $e^+e^-$ annihilation channels up to and including the $ϕ$ meson ($π^+π^-$, $π^0γ$, $ηγ$, $π^+π^-π^0$, $K^+K^-$, $K^0 \bar{K}^0$) and of a set of 10 (mostly radiative) decay widths of light mesons. It also allows to achieve the proof of consistency between the $e^+e^- \to π^+π^-$ annihilation and the $τ^\pm \ra π^\pmπ^0 ν$ decay and gives a solution to the reported problem concerning the measured partial width ratio $Γ(ϕ\to K^+K^-)/Γ(ϕ\to K^0 \bar{K}^0)$. Prospects for improving the VMD based estimates of $a_μ$ are emphasized.

hep-ph↗

arXiv2011

Gravity-driven thin-film flow with negatively buoyant particles

This arXiv article describes the fluid dynamics video on `Gravity-driven thin-film flow with negatively buoyant particles', presented at the 64th Annual Meeting of the APS Division of Fluid Dynamics in Baltimore, MD in November 2011. The video shows three different experiments where a thin film of silicone oil laden with particles, is allowed to flow down an incline under the action of gravity. The videos were recorded at the UCLA Applied Math Laboratory.

physics.flu-dyn↗

arXiv2010

A Global Treatment Of VMD Physics Up To The phi: II. tau Decay and Hadronic Contributions To g-2

Relying on the Hidden Local Symmetry (HLS) model equipped with a mechanism breaking the U(3)/SU(3)/SU(2) symmetries and generating a dynamical vector meson mixing, it has been shown that a global fit successfully describes the cross sections for the e+ e- -> pi+ pi-, e+ e- -> (pi0/eta) gamma and e+ e- -> pi0 pi+ pi- annihilation channels. One extends this global fit in order to include also the dipion spectra from the tau decay, taking into account all reported information on their statistical and systematic errors. A model accounting for lineshape distortions of the rho+- spectrum relative to rho0 is also examined when analyzing the tau data behavior within the global fit framework. One shows that a successful account for e+ e- annihilation data and tau spectra can be simultaneously reached. Then, issues related with non--perturbative hadronic contributions to the muon g-2 are examined in details. It is shown that all e+ e- data considered together allow for improved and motivated estimates for the a_mu(pi+ pi-), the pi+ pi- loop contribution to the muon g-2; for instance, integrated between 0.630 and 0.958 GeV, we find a_mu(pi+ pi-)= 359.62 +- 1.62 (in units of 10^{-10}), a 40% improvement of the current uncertainty. The effects of the various tau samples in the context of a global fit procedure leads to conclude that different lineshape distortions are revealed by the ALEPH, BELLE and CLEO data samples. Relying on global fits to the data quoted above, one also provides motivated estimates of the pi+ pi-, pi0 gamma, eta gamma and pi0 pi+ pi- contributions to a_mu up to 1 GeV with the smallest possible uncertainties. These estimates are based on various global fit configurations, each yielding a good probability.

hep-ph↗

arXiv2009

Can VMD improve the estimate of the muon g-2 ?

We show that a VMD based theoretical input allows for a significantly improved accuracy for the hadronic vacuum polarization of the photon which contributes to the theoretical estimate of the muon g-2. We also show that the only experimental piece of information in the $τ$ decay which cannot be accounted for is the accepted value for ${\rm Br}(τ\ra ππν_τ)$, while the spectum lineshape is in agreement with expectations from $e^+ e^-$ annihilations.

hep-ph↗

arXiv2009

A Global Treatment Of VMD Physics Up To The $ϕ$: I. $e^+e^-$ Annihilations, Anomalies And Vector Meson Partial Widths

The HLS Model, equipped with a mechanism providing the breaking of U(3)/SU(3) symmetry and an isospin symmetry breaking leading naturally to vector meson mixing, has been recently shown to successfully account for $e^+ e^- \ra π^+π^-$ cross section and for the dipion spectrum in $τ$ decay. The present study shows that the full anomalous sector of the HLS model can be considered and is validated by the experimental data. Indeed, this extended model provides a successful simultaneous fit to the $e^+ e^- \ra π^+π^-$ data together with the available data on $e^+ e^- \ra π^0γ$, $e^+ e^- \ra ηγ$ and $e^+ e^- \ra π^0 π^+π^-$ cross sections. It is shown that the fit of these data sets also predicts an accurate description of the $η/η^\prime \ra π^+ π^- γ$ decays fully consistent with the reported information on their branching fractions and spectra. Finally, one also derives from our global fits products of widths of the form $Γ(V \ra f_1)Γ(V \ra e^+ e^-) $ and ratios of the form $Γ(V \ra f_1)/Γ(V \ra f_2)$ describing decays of vector mesons to several non--leptonic final states.

hep-ph↗

arXiv2008

The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach

We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in tau decays. For this purpose, we work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical rho, omega and phi fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the 4--momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vector meson mixing scheme. The model is overconstrained by extending the framework in order to include the description of all meson radiative (V P gamma and P gamma gamma couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking (omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous, consistent and good description of the e+e- and tau dipion spectra. The expression for pion form factor in the latter case is derived from those in the former case by switching off the isospin breaking effects specific to e+e- and switching on those for tau decays. Besides, the model also provides a good account of all decay modes of the form V P gamma, Pgamma gamma as well as the isospin breaking decay modes. It leads us to propose new reference values for the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our description of the pion form factor. Other topics (phi --> K anti K, the rho meson mass and width parameters) are briefly discussed. Therefore, we confirm the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on e+e- and its direct BNL measurement.

hep-ph↗

arXiv2003

The INTEGRAL/IBIS Scientific Data Analysis

The gamma-ray astronomical observatory INTEGRAL, succesfully launched on 17th October 2002, carries two large gamma-ray telescopes. One of them is the coded-mask imaging gamma-ray telescope onboard the INTEGRAL satellite (IBIS) which provides high-resolution (~ 12') sky images of 29deg x 29deg in the energy range from 15 keV to 10 MeV with typical on-axis sensitivity of ~ 1 mCrab at 100 keV (3 sigma, 10E6 s exposure). We report here the general description of the IBIS coded-mask imaging system and of the standard IBIS science data analysis procedures. These procedures reconstruct, clean and combine IBIS sky images providing at the same time detection, identification and preliminary analysis of point-like sources present in the field. Spectral extraction has also been implemented and is based on simultaneous fitting of source and background shadowgram models to detector images. The procedures are illustrated using some of the IBIS data collected during the inflight calibrations and present performance is discussed. The analysis programs described here have been integrated as instrument specific software in the Integral Science Data Center (ISDC) analysis software packages currently used for the Quick Look, Standard and Off-line Scientific Analysis.

astro-ph↗

arXiv2003

In flight calibration of the ISGRI camera

ISGRI, the IBIS low energy camera (15 keV - 1 MeV) on board INTEGRAL, is the first large CdTe gamma-ray imager in orbit. We present here an overview of the ISGRI in-flight calibrations performed during the first months after launch. We discuss the stability of the camera as well as the CdTe pixels response under cosmic radiation. The energy calibra tions were done using lead and tungsten fluorescence lines and the $\mathrm{^{22}Na}$ calibration unit. Thermal effects and charge correction algorithm are discussed, and the resulting energy resolution is presented. The ISGRI background spatial and spectral non-uniformity is also described, and some image correction results are presented.

astro-ph↗

arXiv2003

First Results from the IBIS/ISGRI Data Obtained During the Galactic Plane Scan. II. The Vela Region

We report on INTEGRAL/IBIS observations of the Vela region during a Galactic Plane Scan (hereafter GPS) presenting the IBIS in-flight performances during these operations. Among all the known sources in the field of view we clearly detect 4U 0836-429, Vela X-1, Cen X-3, GX 301-2, 1E 1145.1-6141, and H0918-549 in the 20-40 keV energy range. Only Vela X-1 and GX 301-2 are detected in the 40-80 keV energy range, and no sources are visible above. We present the results of each individual observation (~2200 s exposure), as well as those from the mosaic of these scans.

astro-ph↗

arXiv2003

Anomalous $η/η^\prime$ Decays: The Triangle and Box Anomalies

We examine the decay modes $η/\etp\ra π^+ π^- γ$ within the context of the Hidden Local Symmetry (HLS) Model. Using numerical information derived in previous fits to $VPγ$ and $Ve^+e^-$ decay modes in isolation and the $ρ$ lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as a strong evidence in favor of the box anomaly in the $η/\etp$ decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for $η/\etp\ra π^+ π^- γ$ and $ η/\etp \ra \ggam $ at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two--angle, two--decay--constant) $η-\etp$ mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from fits also matches expectations from previously published fits to the $VPγ$ decay modes in isolation.

nucl-th↗

arXiv2003

The Pion Form Factor Within the Hidden Local Symmetry Model

We analyze a pion form factor formulation which fulfills the Analyticity requirement within the Hidden Local Symmetry (HLS) Model. We show that it implies an $s$--dependent dressing of the $ρ-γ$ VMD coupling and an account of several coupled channels. The corresponding function $F_π(s)$ provides nice fits of the pion form factor data from $s=-0.25$ to $s=1$ GeV$^2$. It is shown that the coupling to $K \bar{K}$ has little effects, while $\omg π^0$ improves significantly the fit quality below the $ϕ$ mass. All parameters, except for the subtraction polynomial coefficients are fixed from the rest of the HLS phenomenology. The fits show consistency with the expected behaviour of $F_π(s)$ at $s=0$ up to ${\cal O} (s^2)$ and with the phase shift data on $δ_1^1(s)$ from threshold to somewhat above the $ϕ$ mass. The $\omg$ sector is also examined in relation with recent data from CMD--2.

nucl-th↗

arXiv2000

Nonlinear denoising of transient signals with application to event related potentials

We present a new wavelet based method for the denoising of {\it event related potentials} ERPs), employing techniques recently developed for the paradigm of deterministic chaotic systems. The denoising scheme has been constructed to be appropriate for short and transient time sequences using circular state space embedding. Its effectiveness was successfully tested on simulated signals as well as on ERPs recorded from within a human brain. The method enables the study of individual ERPs against strong ongoing brain electrical activity.

physics.data-an↗

arXiv1995

Using Pivot Consistency to Decompose and Solve Functional CSPs

Many studies have been carried out in order to increase the search efficiency of constraint satisfaction problems; among them, some make use of structural properties of the constraint network; others take into account semantic properties of the constraints, generally assuming that all the constraints possess the given property. In this paper, we propose a new decomposition method benefiting from both semantic properties of functional constraints (not bijective constraints) and structural properties of the network; furthermore, not all the constraints need to be functional. We show that under some conditions, the existence of solutions can be guaranteed. We first characterize a particular subset of the variables, which we name a root set. We then introduce pivot consistency, a new local consistency which is a weak form of path consistency and can be achieved in O(n^2d^2) complexity (instead of O(n^3d^3) for path consistency), and we present associated properties; in particular, we show that any consistent instantiation of the root set can be linearly extended to a solution, which leads to the presentation of the aforementioned new method for solving by decomposing functional CSPs.

cs.AI↗