54 research outputs found
Sonder l’énergie noire avec les neutrons
There is a deep connection between cosmology - the science of the infinitely large - andparticle physics - the science of the infinitely small. This connection is particularlymanifest in neutron particle physics. Basic properties of the neutron { its ElectricDipole Moment and its lifetime { are intertwined with baryogenesis and nucleosynthesisin the early Universe. I will cover this topic in the first part, that will also serve as anintroduction (or rather a quick recap) of neutron physics and Big Bang cosmology. Then,the rest of the manuscript will be devoted to a new idea: using neutrons to probe modelsof Dark Energy. In the second part, I will present the chameleon theory: a light scalarfield accounting for the late accelerated expansion of the Universe, which interacts withmatter in such a way that it does not mediate a fifth force between macroscopic bodies.However, neutrons can alleviate the chameleon mechanism and reveal the presence of thescalar field with properly designed experiments. In the third part, I will describe a recentexperiment performed with a neutron interferometer at the Institut Laue Langevin thatsets already interesting constraints on the chameleon theory. Last, the chameleon fieldcan be probed by measuring the quantum states of neutrons bouncing over a mirror. Inthe fourth part I will present the status and prospects of the GRANIT experiment atthe ILL
Probing Strongly Coupled Chameleons with Slow Neutrons
We consider different methods to probe chameleons with slow neutrons.
Chameleon modify the potential of bouncing neutrons over a flat mirror in the
terrestrial gravitational field. This induces a shift in the energy levels of
the neutrons which could be detected in current experiments like GRANIT.
Chameleons between parallel plates have a field profile which is bubble-like
and which would modify the phase of neutrons in interferometric experiments. We
show that this new method of detection is competitive with the bouncing neutron
one, hopefully providing an efficient probe of chameleons when strongly coupled
to matter
Strongly Coupled Chameleons and the Neutronic Quantum Bouncer
We consider the potential detection of chameleons using bouncing ultracold
neutrons. We show that the presence of a chameleon field over a planar plate
would alter the energy levels of ultra cold neutrons in the terrestrial
gravitational field. When chameleons are strongly coupled to nuclear matter,
, we find that the shift in energy levels would be
detectable with the forthcoming GRANIT experiment, where a sensitivity of order
one percent of a peV is expected. We also find that an extremely large coupling
would lead to new bound states at a distance of order 2
microns, which is already ruled out by previous Grenoble experiments. The
resulting bound, , is already three orders of magnitude
better than the upper bound, , from precision tests of
atomic spectra.Comment: 4 pages, 1 figure, coincides with the PRL versio
Search for a new short-range spin-dependent force with polarized Helium 3
Measuring the depolarization rate of a He hyperpolarized gas is a
sensitive method to probe hypothetical short-range spin-dependent forces. A
dedicated experiment is being set up at the Institute Laue Langevin in Grenoble
to improve the sensitivity. We presented the status of the experiment at the
10th PATRAS Workshop on Axions, WIMPs and WISPs.Comment: Presented at the 10th PATRAS Workshop on Axions, WIMPs and WISP
Constraining short-range spin-dependent forces with polarized He
We have searched for a short-range spin-dependent interaction using the spin
relaxation of hyperpolarized He. Such a new interaction would be mediated
by a hypothetical light scalar boson with \CP-violating couplings to the
neutron. The walls of the He cell would generate a pseudomagnetic field and
induce an extra depolarization channel. We did not see any anomalous spin
relaxation and we report the limit for interaction ranges between
and : , where () are the (pseudo)scalar coupling
constant, improving the previous best limit by 1 order of magnitude
New Results for Light Gravitinos at Hadron Colliders - Tevatron Limits and LHC Perspectives
We derive Feynman rules for the interactions of a single gravitino with
(s)quarks and gluons/gluinos from an effective supergravity Lagrangian in
non-derivative form and use them to calculate the hadroproduction cross
sections and decay widths of single gravitinos. We confirm the results obtained
previously with a derivative Lagrangian as well as those obtained with the
non-derivative Lagrangian in the high-energy limit and elaborate on the
connection between gauge independence and the presence of quartic vertices. We
perform extensive numerical studies of branching ratios, total cross sections,
and transverse-momentum spectra at the Tevatron and the LHC. From the latest
CDF monojet cross section limit, we derive a new and robust exclusion contour
in the gravitino-squark/gluino mass plane, implying that gravitinos with masses
below to eV are excluded for
squark/gluino-masses below 200 and 500 GeV, respectively. These limits are
complementary to the one obtained by the CDF collaboration,
eV, under the assumption of infinitely heavy squarks and gluinos. For the LHC,
we conclude that SUSY scenarios with light gravitinos will lead to a striking
monojet signal very quickly after its startup.Comment: 30 pages, 12 figures. Tevatron limit improved and unitarity limit
included. Version to be published in Phys. Rev.
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
Electric dipole moment searches: reexamination of frequency shifts for particles in traps
In experiments searching for a nonzero electric dipole moment of trapped
particles, frequency shifts correlated with an applied electric field can be
interpreted as a false signal. One such effect, referred to as the geometric
phase effect, is known to occur in a magnetic field that is nonperfectly
homogeneous. The increase in sensitivity of experiments demands improved
theoretical description of this effect. In the case of fast particles, like
atoms at room temperature and low pressure, the validity of established
theories was limited to a cylindrical confinement cell in a uniform gradient
with cylindrical symmetry. We develop a more general theory valid for an
arbitrary shape of the magnetic field as well as for arbitrary geometry of the
confinement cell. Our improved theory is especially relevant for experiments
measuring the neutron electric dipole moment with an atomic comagnetometer. In
this context, we have reproduced and extended earlier numerical studies of the
geometric phase effect induced by localized magnetic impurities
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