557 research outputs found
Quantum dynamics of particles in a discrete two-branes world model: Can matter particles exchange occur between branes?
In a recent paper, a model for describing the quantum dynamics of massive
particles in a non-commutative two-sheeted spacetime was proposed. This model
considers a universe made with two spacetime sheets embedded in a 5D bulk where
the fifth dimension is restricted to only two points. It was shown that this
construction has several important consequences for the quantum dynamics of
massive particles. Most notably, it was demonstrated that a coupling arises
between the two sheets allowing matter exchange in presence of intense magnetic
vector potentials. In this paper, we show that non-commutative geometry is not
absolutely necessary to obtain such a result since a more traditional approach
allows one to reach a similar conclusion. The fact that two different
approaches provide similar results suggests that standard matter exchange
between branes might finally occur contrary to conventional belief.Comment: 11 pages, no figures. Final version. Published in Acta Physica
Polonica
Plausible "faster-than-light" displacements in a two-sheeted spacetime
In this paper, we explore the implications of a two-point discretization of
an extra-dimension in a five-dimensional quantum setup. We adopt a pragmatic
attitude by considering the dynamics of spin-half particles through the
simplest possible extension of the existing Dirac and Pauli equations. It is
shown that the benefit of this approach is to predict new physical phenomena
while maintaining the number of constitutive hypothesis at minimum. As the most
striking feature of the model, we demonstrate the possibility of fermionic
matter oscillations between the two four-dimensional sections and hyper-fast
displacements in case of asymmetric warping (without conflicting special
relativity). This result, similar to previous reported ones in brane-world
theories, is completely original as it is derived by using quantum mechanics
only without recourse to general relativity and bulk geodesics calculation. The
model allows causal contact between normally disconnected regions. If it proves
to be physically founded, its practical aspects could have deep implications
for the search of extra-dimensions.Comment: 17 pages, 1 figure. Final version. Accepted for publication in Phys.
Rev.
Worker flows, job flows and establishment wage differentials : analyzing the case of France
We address the relation between establishment wage differentials and worker flows, i.e. the churning rate and the quit rate. Our analysis is based on a linked employer-employee dataset covering the French private non-farm sector from 2002 to 2005. Our estimations support the hypothesis that wage premium is an efficient human resource management tool to stabilize workers : churning rates are lower in high-paying firms due to lower quit rates. We further show that the relation is not linear, and it differs among skill groups and according to establishment size : it is strongest for low-wage levels, for low-skilled workers and in large establishments.Establishment wage effects, worker flows, churning rate, quite rate, linked employer-employee panel data, France.
Laser frequency combs and ultracold neutrons to probe braneworlds through induced matter swapping between branes
This paper investigates a new experimental framework to test the braneworld
hypothesis. Recent theoretical results have shown the possibility of matter
exchange between branes under the influence of suitable magnetic vector
potentials. It is shown that the required conditions might be achieved with
present-day technology. The experiment uses a source of pulsed and coherent
electromagnetic radiation and relies on the Hansch frequency comb technique
well-known in ultrahigh-precision spectroscopy. A good matter candidate for
testing the hypothesis is a polarized ultracold neutron gas for which the
number of swapped neutrons is measured.Comment: 14 pages, 4 figures. Published version. Published in Phys. Rev.
Matter swapping between two braneworlds from the equivalence between two-brane worlds and noncommutative two-sheeted spacetimes
It is shown that a two-brane world made of two domain walls can be seen as a
noncommutative two-sheeted spacetime under certain assumptions. This
equivalence implies a model-independent phenomenology: Matter swapping between
the two 3-branes (or sheets) is predicted through fermionic oscillations
induced by magnetic vector potentials. This phenomenon, which might be
experimentally studied, could reveal the existence of extra dimensions in a new
and very affordable way.Comment: 3 pages. Published in the proceedings of the 2011 Europhysics
Conference on High Energy Physics - HEP 2011, July 21-27 2011, Grenoble,
France. Poster session contribution. The manuscript has overlap with
arXiv:0903.2498 and arXiv:0809.2060, which are extensively more detailed. The
present paper is deposited as a convenient summary of previous works and
further studie
Equivalence between domain-walls and "noncommutative" two-sheeted spacetimes: Model-independent matter swapping between branes
We report a mathematical equivalence between certain models of universe
relying on domain-walls and noncommutative geometries. It is shown that a
two-brane world made of two domain-walls can be seen as a "noncommutative"
two-sheeted spacetime under certain assumptions. This equivalence also implies
a model-independent phenomenology which is presently studied. Matter swapping
between the two branes (or sheets) is predicted through fermionic oscillations
induced by magnetic vector potentials. This phenomenon, which might be
experimentally studied, could reveal the existence of extra dimensions in a new
and accessible way.Comment: 18 pages, 1 figure. Final version. Published in Phys. Rev.
Modélisation du milieu interstellaire sur la Grille
International audienceModélisation du milieu interstellaire sur la Grill
Meat and cancer: haemoglobin and haemin in a low calcium diet promote colorectal carcinogenesis at the aberrant crypt stage in rats
High intake of red meat, but not of white meat, is associated with an increased risk of colon cancer. However, red meat does not promote cancer in rodents. Haemin, added to low-calcium diets, increases colonic proliferation, and haemoglobin, added to high-fat diets, increases the colon tumour incidence in rats, an effect possibly due to peroxyl radicals. We thus speculated that haem might be the promoting agent in meat, and that prevention strategies could use calcium and antioxidants. These hypotheses were tested in rats at the aberrant crypt foci (ACF) stage at 100 days. F344 rats (n = 124) were given an injection of azoxymethane and were then randomized to 11 groups fed with low-calcium (20 micro mol/g) AIN76-based diets, containing 5% safflower oil. Haemin (0.25, 0.5 and 1.5 micro mol/g) or haemoglobin (1.5 and 3 micro mol haem/g) was added to five experimental diets, compared with a control diet without haem. Three other high-haemin diets (1.5 micro mol/g) were supplemented with calcium (250 micro mol/g), antioxidant butylated hydroxyanisole and rutin (0.05% each), and olive oil, which replaced safflower oil. Faecal water was assayed for lipid peroxidation by thiobarbituric acid reactive substances (TBARs) test, and for cytolytic activity. Haemin strikingly increased the ACF size, dose-dependently, from 2.6 to 11.4 crypts/ACF (all P < 0.001). The high-haemin diet also increased the number of ACF per colon (P < 0.001). Promotion was associated with increased faecal water TBARs and cytotoxicity. Calcium, olive oil and antioxidants each inhibited the haemin-induced ACF promotion, and normalized the faecal TBARs and cytotoxicity. The haemoglobin diets increased the number of ACF and faecal TBARs, but not the ACF size or the faecal cytotoxicity. In conclusion, dietary haemin is the most potent known ACF promoter. Haemoglobin is also a potent promoter of colorectal carcinogenesis. The results suggest that myoglobin in red meat could promote colon cancer. Diets high in calcium, or in oxidation-resistant fats, may prevent the possible cancer-promoting effect of red meat
Probing the braneworld hypothesis with a neutron-shining-through-a-wall experiment
The possibility for our visible world to be a 3-brane embedded in a
multidimensional bulk is at the heart of many theoretical edifices in
high-energy physics. Probing the braneworld hypothesis is thus a major
experimental challenge. Following recent theoretical works showing that matter
swapping between braneworlds can occur, we propose a
neutron-shining-through-a-wall experiment. We first show that an intense
neutron source such as a nuclear reactor core can induce a hidden neutron flux
in an adjacent hidden braneworld. We then describe how a low-background
detector can detect neutrons arising from the hidden world and quantify the
expected sensitivity to the swapping probability. As a proof of concept, a
constraint is derived from previous experiments.Comment: 12 pages, 4 figures, final version published in Physical Review
Artificially induced positronium oscillations in a two-sheeted spacetime: consequences on the observed decay processes
Following recent theoretical results, it is suggested that positronium (Ps)
might undergo spontaneous oscillations between two 4D spacetime sheets whenever
subjected to constant irrotational magnetic vector potentials. We show that
these oscillations that would come together with o-Ps/p-Ps oscillations should
have important consequences on Ps decay rates. Experimental setup and
conditions are also suggested for demonstrating in non accelerator experiments
this new invisible decay mode.Comment: 9 pages, 2 figures. Minor form correction. Accepted for publication
in Int. J. of Modern Physics
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