Superfluid properties of one-component Fermi gas with an anisotropic p-wave interaction

We investigate superfluid properties and strong-coupling effects in a one-component Fermi gas with an anisotropic p-wave interaction. Within the framework of the Gaussian fluctuation theory, we determine the superfluid transition temperature $T_{\rm c}$, as well as the temperature $T_0$ at which the phase transition from the $p_x$-wave pairing state to the $p_x+ip_y$-wave state occurs below $T_{\rm c}$. We also show that while the anisotropy of the p-wave interaction enhances $T_{\rm c}$ in the strong-coupling regime, it suppresses $T_0$.Comment: 7 pages, 3 figures, proceedings of QFS 201

All-particle cosmic ray energy spectrum measured with 26 IceTop stations

We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122 km^2. The analysis investigated the energy spectrum from 1 to 100 PeV measured for three different zenith angle ranges between 0{\deg} and 46{\deg}. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles {\theta} < 30{\deg}, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed between 3.5 and 4.32 PeV, depending on composition assumption. Spectral indices above the knee range from -3.08 to -3.11 depending on primary mass composition assumption. Moreover, an indication of a flattening of the spectrum above 22 PeV were observed.Comment: 38 pages, 17 figure

Dark Energy and Gravity

I review the problem of dark energy focusing on the cosmological constant as the candidate and discuss its implications for the nature of gravity. Part 1 briefly overviews the currently popular `concordance cosmology' and summarises the evidence for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as the candidate and emphasises why no other approach really solves the conceptual problems usually attributed to the cosmological constant. Part 2 describes some of the approaches to understand the nature of the cosmological constant and attempts to extract the key ingredients which must be present in any viable solution. I argue that (i)the cosmological constant problem cannot be satisfactorily solved until gravitational action is made invariant under the shift of the matter lagrangian by a constant and (ii) this cannot happen if the metric is the dynamical variable. Hence the cosmological constant problem essentially has to do with our (mis)understanding of the nature of gravity. Part 3 discusses an alternative perspective on gravity in which the action is explicitly invariant under the above transformation. Extremizing this action leads to an equation determining the background geometry which gives Einstein's theory at the lowest order with Lanczos-Lovelock type corrections. (Condensed abstract).Comment: Invited Review for a special Gen.Rel.Grav. issue on Dark Energy, edited by G.F.R.Ellis, R.Maartens and H.Nicolai; revtex; 22 pages; 2 figure

Extended investigation of superdeformed bands in 151,152^{151,152}Tb nuclei

A detailed study of known and new SD bands in Tb isotopes has been performed with the use of the EUROBALL IV -ray array. The high-statistics data set has allowed for the extension of known SD bands at low and high spins by new -ray transitions. These transitions, as it turns out, correspond to the rotational frequencies where the principal superdeformed gaps (Z=66,N=86) close giving rise to up- or down-bending mechanisms. This enables to attribute the underlying theoretical configurations with much higher confidence as compared to the previous identifications. Five new SD bands have been discovered, three of them assigned to the 152Tb and the two others to the 151Tb nuclei. Nuclear mean-field calculations have been used to interpret the structure of known SD bands as well as of the new ones in terms of nucleonic configurations

Spectroscopie Mössbauer de 57Fe et 119Sn par détection des électrons de conversion et auger application à des études de surface

We have built a system which allows the measurement of Mössbauer spectra as a function of the energy of conversion and Auger electrons. The interest of the technique developed in this work arises from the low range of the electrons in a solid so that Mössbauer spectroscopy deals only with a thin superficial layer of the sample (0.3 μ for 57Fe and 3 μ for 119Sn). Monochromatic electrons are emitted and the loss of their energy is related to the depth of material they come from. Selecting the electrons in terms of their energy with the use of a β spectrometer thus allows an analysis of layers of known thickness and depth. Some examples of application on iron and tin samples are described.Nous avons construit un appareil permettant le relevé de spectres Mössbauer en fonction de l'énergie des électrons de conversion et Auger. L'intérêt de la technique développée dans ce travail est lié au faible parcours des électrons dans les solides, ce qui permet de limiter l'analyse par spectroscopie Mössbauer à une couche superficielle mince de l'échantillon (0,3 μ pour le 57Fe et 3 μ pour 119Sn). Les électrons sont monocinétiques à l'émission et leur perte d'énergie est fonction de l'épaisseur de matière traversée. La sélection en énergie des électrons à l'aide d'un spectromètre β permet donc une analyse sélective de couches de profondeur et d'épaisseur déterminées. Quelques exemples d'application sur des échantillons de fer et d'étain sont décrits