904 research outputs found
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 framework, we add here
the space time parameters. We show how and
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
. 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 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 as the
average delay on the photon propagation. We then show that the vacuum
permittivity and permeability 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
- …