The ΛCDM standard model, although an excellent parametrization of the present cosmological data, contains two as yet unobserved components, dark matter and dark energy, that constitute more than 95% ...of the Universe. Faced with this unsatisfactory situation, we study an unconventional cosmology, the Dirac-Milne universe, a matter-antimatter symmetric cosmology, in which antimatter is supposed to present a negative active gravitational mass. The main feature of this cosmology is the linear evolution of the scale factor with time, which directly solves the age and horizon problems of a matter-dominated universe. We study the concordance of this model to the cosmological test of type Ia supernovae distance measurements and calculate the theoretical primordial abundances of light elements for this cosmology. We also show that the acoustic scale of the cosmic microwave background naturally emerges at the degree scale despite an open geometry.
The EDELWEISS-II Collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The ...combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of γ-induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4×10−8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.
The Einstein classical Weak Equivalence Principle states that the trajectory of a particle is independent of its composition and internal structure when it is only submitted to gravitational forces. ...This fundamental principle has never been directly tested with antimatter. However, theoretical models such as supergravity may contain components inducing repulsive gravity, thus violating this principle. The GBAR project (Gravitational Behaviour of Antihydrogen at Rest) proposes to measure the free fall acceleration of ultracold neutral antihydrogen atoms in the terrestrial gravitational field. The experiment consists in preparing antihydrogen ions (one antiproton and two positrons) and sympathetically cool them with Be
+
ions to a few 10
μ
K. The ultracold ions will then be photoionized just above threshold, and the free-fall time over a known distance measured. In this work, the GBAR project is described as well as possible improvements that use quantum reflection of antihydrogen on surfaces to use quantum methods of measurements.
The final results of the EDELWEISS-I dark matter search using cryogenic heat-and-ionization Ge detectors are presented. The final data sample corresponds to an increase by a factor five in exposure ...relative to the previously published results. A recoil energy threshold of 13 keV or better was achieved with three 320g detectors working simultaneously over four months of stable operation. Limits on the spin-independent cross-section for the scattering of a WIMP on a nucleon are derived from an accumulated fiducial exposure of 62 kg.d.
The EDELWEISS-II Collaboration has performed a direct search for WIMP dark matter with an array of ten 400 g heat-and-ionization cryogenic detectors equipped with interleaved electrodes for the ...rejection of near-surface events. Six months of continuous operation at the Laboratoire Souterrain de Modane have been achieved. The observation of one nuclear recoil candidate above 20 keV in an effective exposure of 144 kg d is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 1.0×10−7 pb is excluded at 90% CL for a WIMP mass of 80 GeV/c2. This result demonstrates for the first time the very high background rejection capabilities of these simple and robust detectors in an actual WIMP search experiment.
The EDELWEISS experiment has improved its sensitivity for the direct search for WIMP dark matter. In the recoil energy range relevant for WIMP masses below 10 TeV/
c
2, no nuclear recoils were ...observed in the fiducial volume of a heat-and-ionization cryogenic Ge detector operated in the low-background environment of the Laboratoire Souterrain de Modane in the Fréjus Tunnel, during an effective exposure of 7.4 kg
d. This result is combined with the previous EDELWEISS data to derive a limit on the cross-section for spin-independent interaction of WIMPs and nucleons as a function of WIMP mass, using standard nuclear physics and astrophysical assumptions. This limit excludes at more than 99.8% CL a WIMP candidate with a mass of 44 GeV/
c
2 and a cross-section of 5.4×10
−6 pb, as reported by the DAMA Collaboration. A first sample of supersymmetric models are also excluded at 90% CL.
A multi-tiered data structure, analysis toolkit and data processing management system has been constructed using ROOT and CouchDB. This system is well suited for experiments that acquire many ...computer files of raw data over the course of months or years, that are distributed to different computing centers and further reduced in size by several steps of data processing. Data handling for experiments searching for rare events extracted from digitized pulse traces typically fit this description. An implementation of this system has been constructed for the EDELWEISS-III experiment and is described here in some detail. This solution may also serve as a prototype system for the proposed EURECA experiment.
This paper presents our interpretation and understanding of the different backgrounds in the EDELWEISS-I data sets. We analyze in detail the several populations observed, which include gammas, ...alphas, neutrons, thermal sensor events and surface events, and try to combine all data sets to provide a coherent picture of the nature and localization of the background sources. In light of this interpretation, we draw conclusions regarding the background suppression scheme for the EDELWEISS-II phase.
Using as an illustration cryogenic detectors, I discuss a few innovative ideas that resulted in significant progress in sensitivity. After presenting the main classes of sensors, I summarize the ...impact of cryogenic detectors on Dark Matter, one of the outstanding questions in astroparticle physics and cosmology. I briefly review some applications in astrophysics and other fields.
PDF
