Does the speed of light depend upon the vacuum ?

We propose a quantum model for the vacuum filled of virtual particle pairs. The main originality of this model is to define a density and a life-time of the virtual particles. Compared to the usual QED $(p,E)$ framework, we add here the $(x,t)$ space time parameters. We show how $\epsilon_0$ and $\mu_0$ originate from the polarization and the magnetization of these virtual pairs when the vacuum is stressed by an electrostatic or magnetostatic field respectively. We obtain numerical values very close to the measured values. The exact equalities constraint the free parameters of our vacuum model. Then we show that if we simply model the propagation of a photon in vacuum as a succession of transient captures with virtual pairs, we can derive a finite velocity of the photon with a magnitude close to the measured speed of light $c$. Again this is the occasion to adjust better our vacuum model. Since the transit time of a photon is a statistical process we expect it to be fluctuating and this translates into a fluctuation of $c$ which, if measured, would bring another piece of information on the vacuum. When submitted to a stress the vacuum may change and this will induce a variation in the electromagnetic constants. We show this to be the case around a gravitational mass. It gives a physical interpretation of a varying vacuum refractive index equivalent to the curved space-time in General Relativity. The known measurements of the deflection of light by a mass, the Shapiro delay and the gravitational redshift do bring constraints on the way inertial masses should depend upon the vacuum. At last some experimental predictions are proposed.Comment: 25 page

Search for neutrinoless double beta decay with the NEMO-3 detector: first results

The NEMO-3 detector, which has been operating in the Frejus Underground Laboratory since February 2003, is devoted to searching for neutrinoless double beta decay (\beta\beta 0 \nu). The expected performance of the detector has been successfully achieved. Half-lives of the two neutrinos double beta decay (\beta\beta 2 \nu$) have been measured for ^{100} Mo, ^{82}Se, ^{96}Zr, ^{116}Cd and ^{150}Nd. After 265 days of data collection from February 2003 until March 2004, no evidence for neutrinoless double beta decay (\beta\beta 0 \nu) was found from \sim 7 kg of ^{100} Mo and \sim 1 kg of ^{82} Se. The corresponding lower limits for the half-lives are 3.5 \times 10^{23} years at 90% C.L for ^{100} Mo and 1.9 \times 10^{23} years for ^{82}Se. Limits for the effective Majorana neutrino mass are < \hspace{-0.5mm} m_{\nu} \hspace{-0.5mm} > < 0.7-1.2 eV for ^{100} Mo and \linebreak < \hspace{-0.5mm} m_{\nu \hspace{-0.5mm} > < 1.3-3.2 eV for ^{82}Se. Radon is the dominant background today and a Radon-free purification system will be in operation by the end of september 2004. The NEMO-3 expected sensitivity after 5 years of data is 0.2 eV.Comment: 5 pages, 4 figures, invited talk given at the 21st International Conference on Neutrino Physics and Astrophysics, (Neutrino 2004) 14-19 June 2004, College de France - Pari

A mechanism giving a finite value to the speed of light, and some experimental consequences

We admit that the vacuum is not empty but is filled with continuously appearing and disappearing virtual fermion pairs. We show that if we simply model the propagation of the photon in vacuum as a series of transient captures within the virtual pairs, we can derive the finite light velocity $c$ as the average delay on the photon propagation. We then show that the vacuum permittivity $\epsilon_0$ and permeability $\mu_0$ originate from the polarization and the magnetization of the virtual fermions pairs. Since the transit time of a photon is a statistical process within this model, we expect it to be fluctuating. We discuss experimental tests of this prediction. We also study vacuum saturation effects under high photon density conditions.Comment: Submitted to International Journal of Modern Physics A. arXiv admin note: substantial text overlap with arXiv:1106.399

Optical Properties of the DIRC Fused Silica Cherenkov Radiator

The DIRC is a new type of Cherenkov detector that is successfully operating as the hadronic particle identification system for the BABAR experiment at SLAC. The fused silica bars that serve as the DIRC's Cherenkov radiators must transmit the light over long optical pathlengths with a large number of internal reflections. This imposes a number of stringent and novel requirements on the bar properties. This note summarizes a large amount of R&D that was performed both to develop specifications and production methods and to determine whether commercially produced bars could meet the requirements. One of the major outcomes of this R&D work is an understanding of methods to select radiation hard and optically uniform fused silica material. Others include measurement of the wavelength dependency of the internal reflection coefficient, and its sensitivity to surface contaminants, development of radiator support methods, and selection of good optical glue.Comment: 36 pages, submitted to Nuclear Instruments and Methods

The narrow X-ray tail and double H-alpha tails of ESO 137-002 in Abell 3627

We present the analysis of a deep Chandra observation of a ~2L_* late-type galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal a long (>40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on the upstream side of the tail. The tail is most likely caused by the nearly edge-on stripping of ESO 137-002's ISM by ram pressure, compared to the nearly face-on stripping of ESO 137-001 discussed in our previous work. Spectral analysis of individual regions along the tail shows that the gas throughout it has a rather constant temperature, ~1 keV, very close to the temperature of the tails of ESO 137-001, if the same atomic database is used. The derived gas abundance is low (~0.2 solar with the single-kT model), an indication of the multiphase nature of the gas in the tail. The mass of the X-ray tail is only a small fraction (<5%) of the initial ISM mass of the galaxy, suggesting that the stripping is most likely at an early stage. However, with any of the single-kT, double-kT and multi-kT models we tried, the tail is always "over-pressured" relative to the surrounding ICM, which could be due to the uncertainties in the abundance, thermal vs. non-thermal X-ray emission, or magnetic support in the ICM. The H-alpha data from SOAR show a ~21 kpc tail spatially coincident with the X-ray tail, as well as a secondary tail (~12 kpc long) to the east of the main tail diverging at an angle of ~23 degrees and starting at a distance of ~7.5 kpc from the nucleus. At the position of the secondary H-alpha tail, the X-ray emission is also enhanced at the ~2 sigma level. We compare the tails of ESO 137-001 and ESO 137-002, and also compare the tails to simulations. Both the similarities and differences of the tails pose challenges to the simulations. Several implications are briefly discussed.Comment: 15 pages, 6 figures, accepted for publication in Ap

Global linear stability analysis of kinetic Trapped Ion Mode (TIM) turbulence in tokamak plasma using spectral method

Trapped ion modes (TIM) which belong to the family of ion temperature gradient (ITG) modes, is one of the important ingredients in heat turbulent transport at the ion scale in tokamak plasmas. It is essential to properly estimate their linear growth rate to understand their influence on ion-scale turbulent transport. A global linear analysis of a reduced gyro-bounce kinetic model for trapped particle modes is performed, and a spectral method is proposed to solve the dispersion relation. Importantly, the radial profile of the particle drift velocity is taken into account in the linear analysis by considering the exact magnetic flux {\psi} dependency of the equilibrium Hamiltonian H_{eq}({\psi}) in the quasi-neutrality equation and equilibrium gyro-bounce averaged distribution function F_{eq} . Using this spectral method, linear growth-rates of TIM instability in presence of different temperature profiles and precession frequencies of trapped ions, with an approximated constant Hamiltonian and the exact {\psi} dependent equilibrium Hamiltonian, are investigated. The growth-rate depends on the logarithmic gradient of temperature \kappa_{T} , density \kappa_{n} and equilibrium Hamiltonian \kappa_{\Lambda} . With the exact {\psi} dependent Hamiltonian, the growth rates and potential profiles are modified significantly, compared to the cases with approximated constant Hamiltonian. All the results from the global linear analysis agree with a semi-Lagrangian based linear Vlasov solver with a good accuracy. This spectral method is very fast and requires very less computation resources compared to a linear version of Vlasov-solver based on a semi-Lagrangian scheme

The Globular Cluster System of NGC 5846 Revisited: Colours, Sizes and X-Ray Counterparts

NGC 5846 is a giant elliptical galaxy with a previously well studied globular cluster system (GCS), known to have a bimodal colour distribution with a remarkably high red fraction. Here we revisit the central galaxy regions searching for new globular cluster (GC) candidates, and measuring, magnitudes, colours and sizes for them. We also search for their X-ray counterparts. We use archival Hubble Space Telescope WFPC2 images, from which we modelled and subtracted the host light distribution and increased the available sample of GCs. We performed photometry on the central objects, and measured sizes and equatorial coordinates for the entire system known in this galaxy. We detect two dozen previously unknown GC candidates in the central regions. Reliable sizes are obtained for about 60 GCs; their typical effective radii are in the range 3-5 pc. The largest clusters are located in the central regions. We find 7 X-ray counterparts to globular clusters, most of them in the central region. They are among the most luminous X-ray sources in NGC 5846. They are also optically luminous, compact and belong to the red subpopulation.Comment: 8 pages, 9 figures, A&A accepte

The Problem of Marginality in Model Reductions of Turbulence

Reduced quasilinear (QL) and nonlinear (gradient-driven) models with scale separations, commonly used to interpret experiments and to forecast turbulent transport levels in magnetised plasmas are tested against nonlinear models without scale separations (flux-driven). Two distinct regimes of turbulence -- either far above threshold or near marginal stability -- are investigated with Boltzmann electrons. The success of reduced models especially hinges on the reproduction of nonlinear fluxes. Good agreement between models is found above threshold whilst reduced models would significantly underpredict fluxes near marginality, overlooking mesoscale flow organisation and turbulence self-advection. Constructive prescriptions whereby to improve reduced models is discussed